Anti-Müllerian hormone and letrozole levels in boys with constitutional delay of growth and puberty treated with letrozole or testosterone

STUDY QUESTION

Does treatment of constitutional delay of growth and puberty (CDGP) in boys with aromatase inhibitor letrozole (Lz) or conventional low-dose testosterone (T) have differing effects on developing seminiferous epithelium?

SUMMARY ANSWER

Anti-Müllerian hormone (AMH) declined similarly in both treatment groups, and the two Sertoli cell-derived markers (AMH and inhibin B (iB)) exhibited differing responses to changes in gonadotrophin milieu.

WHAT IS KNOWN ALREADY

Boys with CDGP may benefit from puberty-inducing medication. Peroral Lz activates gonadotrophin secretion, whereas intramuscular low-dose T may transiently suppress gonadotrophins and iB.

STUDY DESIGN, SIZE, DURATION

Sera of 28 boys with CDGP who participated in a randomised, controlled, open-label trial at four paediatric centres in Finland between August 2013 and January 2017 were analysed. The patients were randomly assigned to receive either Lz (2.5 mg/day) (n = 15) or T (1 mg/kg/month) (n = 13) for 6 months.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The 28 patients were at least 14 years of age, showed first signs of puberty, wanted medical attention for CDGP and were evaluated at 0, 3, 6 and 12 months of visits. AMH levels were measured with an electrochemiluminescence immunoassay and Lz levels with liquid chromatography coupled with tandem mass spectrometry.

MAIN RESULTS AND THE ROLE OF CHANCE

AMH levels decreased in both treatment groups during the 12-month follow-up (P < 0.0001). Between 0 and 3 months, the changes in gonadotrophin levels (increase in the Lz group, decrease in the T group) correlated strongly with the changes in levels of iB (FSH vs iB, r = 0.55, P = 0.002; LH vs iB, r = 0.72, P < 0.0001), but not with the changes in AMH (P = NS). At 12 months, AMH levels did not differ between the groups (P = NS). Serum Lz levels (range, 124-1262 nmol/L) were largely explained by the Lz dose per weight (at 3 months r = 0.62, P = 0.01; at 6 months r = 0.52, P = 0.05). Lz levels did not associate with changes in indices of hypothalamic-pituitary-gonadal axis activity or Sertoli cell markers (in all, P = NS).

LIMITATIONS, REASONS FOR CAUTION

The original trial was not blinded for practical reasons and included a limited number of participants.

WIDER IMPLICATIONS OF THE FINDINGS

In early puberty, treatment-induced gonadotrophin stimulus was unable to counteract the androgen-mediated decrease in AMH, while changes in iB levels were associated with changes in gonadotrophin levels. AMH decreased similarly in both groups during the treatment, reassuring safety of developing seminiferous epithelium in both treatment approaches. Since a fixed dose of Lz induced variable serum Lz levels with a desired puberty-promoting effect in all boys, more research is needed to aim at a minimal efficient dose per weight.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Academy of Finland, the Foundation for Pediatric Research, the Emil Aaltonen Foundation, Sigrid Juselius Foundation and Helsinki University Hospital Research Funds. The authors have nothing to disclose.

TRIAL REGISTRATION NUMBER

NCT01797718.

The effects of intravenous lipid emulsion on hemodynamic recovery and myocardial cell mitochondrial function after bupivacaine toxicity in anesthetized pigs

Local anesthetic toxicity is thought to be mediated partly by inhibition of cardiac mitochondrial function. Intravenous (i.v.) lipid emulsion may overcome this energy depletion, but doses larger than currently recommended may be needed for rescue effect. In this randomized study with anesthetized pigs, we compared the effect of a large dose, 4 mL/kg, of i.v. 20% Intralipid® ( n = 7) with Ringer’s acetate ( n = 6) on cardiovascular recovery after a cardiotoxic dose of bupivacaine. We also examined mitochondrial respiratory function in myocardial cell homogenates analyzed promptly after needle biopsies from the animals. Bupivacaine plasma concentrations were quantified from plasma samples. Arterial blood pressure recovered faster and systemic vascular resistance rose more rapidly after Intralipid than Ringer’s acetate administration ( p < 0.0001), but Intralipid did not increase cardiac index or left ventricular ejection fraction. The lipid-based mitochondrial respiration was stimulated by approximately 30% after Intralipid ( p < 0.05) but unaffected by Ringer’s acetate. The mean (standard deviation) area under the concentration–time curve (AUC) of total bupivacaine was greater after Intralipid (105.2 (13.6) mg·min/L) than after Ringer’s acetate (88.1 (7.1) mg·min/L) ( p = 0.019). After Intralipid, the AUC of the lipid-un-entrapped bupivacaine portion (97.0 (14.5) mg·min/L) was 8% lower than that of total bupivacaine ( p < 0.0001). To conclude, 4 mL/kg of Intralipid expedited cardiovascular recovery from bupivacaine cardiotoxicity mainly by increasing systemic vascular resistance. The increased myocardial mitochondrial respiration and bupivacaine entrapment after Intralipid did not improve cardiac function.

Intravenous Lipid Emulsion for Levobupivacaine Intoxication in Acidotic and Hypoxaemic Pigs

Intravenous lipid emulsion is, in some countries, the recommended treatment for local anaesthetic toxicity. Systemic local anaesthetic toxicity results in hypoxaemia and acidosis, and whether this influences the effects of lipid therapy on drug concentrations and cardiovascular recovery is currently unknown. Twenty anaesthetised pigs were given a 3 mg/kg bolus of levobupivacaine followed by a five-minute phase of hypoventilation and 1 mmol/kg of lactic acid over one minute. After lactic acid infusion, pigs were treated, in randomised order, with either 20% lipid emulsion or Ringer's acetate for 30 minutes: a 1.5 ml/kg bolus followed by a 0.25 ml/kg/minute infusion. Haemodynamic parameters were recorded and blood samples were collected for pharmacokinetic analysis. There was no difference between the groups in the area under the plasma levobupivacaine concentration–time curve (AUC) or between that and AUC of unentrapped levobupivacaine in the Lipid group, or in the plasma half-lives. The cardiovascular outcome and normalisation of the electrocardiogram were similar in both groups. Five pigs developed marked hypotension: one in both groups died, while two in the Lipid group and one in the Ringer group needed adrenaline. Administration of lipid emulsion did not improve cardiovascular recovery from levobupivacaine toxicity exacerbated by acidosis and hypoxaemia. Lipid emulsion did not entrap levobupivacaine or affect levobupivacaine pharmacokinetics.

Potent mechanism-based inhibition of CYP3A4 by imatinib explains its liability to interact with CYP3A4 substrates

BACKGROUND AND PURPOSE

Imatinib, a cytochrome P450 2C8 (CYP2C8) and CYP3A4 substrate, markedly increases plasma concentrations of the CYP3A4/5 substrate simvastatin and reduces hepatic CYP3A4/5 activity in humans. Because competitive inhibition of CYP3A4/5 does not explain these in vivo interactions, we investigated the reversible and time-dependent inhibitory effects of imatinib and its main metabolite N-desmethylimatinib on CYP2C8 and CYP3A4/5 in vitro.

EXPERIMENTAL APPROACH

Amodiaquine N-deethylation and midazolam 1'-hydroxylation were used as marker reactions for CYP2C8 and CYP3A4/5 activity. Direct, IC(50) -shift, and time-dependent inhibition were assessed with human liver microsomes.

KEY RESULTS

Inhibition of CYP3A4 activity by imatinib was pre-incubation time-, concentration- and NADPH-dependent, and the time-dependent inactivation variables K(I) and k(inact) were 14.3 µM and 0.072 in(-1) respectively. In direct inhibition experiments, imatinib and N-desmethylimatinib inhibited amodiaquine N-deethylation with a K(i) of 8.4 and 12.8 µM, respectively, and midazolam 1'-hydroxylation with a K(i) of 23.3 and 18.1 µM respectively. The time-dependent inhibition effect of imatinib was predicted to cause up to 90% inhibition of hepatic CYP3A4 activity with clinically relevant imatinib concentrations, whereas the direct inhibition was predicted to be negligible in vivo.

CONCLUSIONS AND IMPLICATIONS

Imatinib is a potent mechanism-based inhibitor of CYP3A4 in vitro and this finding explains the imatinib-simvastatin interaction and suggests that imatinib could markedly increase plasma concentrations of other CYP3A4 substrates. Our results also suggest a possibility of autoinhibition of CYP3A4-mediated imatinib metabolism leading to a less significant role for CYP3A4 in imatinib biotransformation in vivo than previously proposed.

Itraconazole, a potent inhibitor of P-glycoprotein, moderately increases plasma concentrations of oral morphine

BACKGROUND

Individual variation in opioid response is considerable, partly due to pharmacokinetic factors. Transporter proteins are becoming increasingly interesting also in the pharmacokinetics of opioids. The efflux transporter P-glycoprotein can affect gastrointestinal absorption and tissue distribution, particularly brain access of many opioids. The aim of this study was to evaluate whether itraconazole, which is a potent inhibitor of P-glycoprotein and CYP3A4, would change the pharmacokinetics or the pharmacodynamics of oral morphine.

METHODS

Twelve healthy male volunteers ingested, in a randomized crossover study, once daily 200 mg itraconazole or placebo for 4 days. On day 4, 1 h after the last pre-treatment dose, the subjects ingested 0.3 mg/kg morphine. Blood samples for the determination of plasma morphine, morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G) and itraconazole concentrations were drawn up to 48 h after morphine ingestion. Pharmacodynamic effects were evaluated using a questionnaire, visual analogue scales, a reaction time test, the Digit Symbol Substitution Test and the Critical Flicker Fusion Test.

RESULTS

Itraconazole increased the mean area under the plasma concentration-time curve [AUC (0-9)] of morphine by 29% (P=0.002), its AUC (0-48) by 22% (P=0.013) and its peak plasma concentration by 28% (P=0.035). Itraconazole did not significantly affect the pharmacokinetic variables of M3G or M6G or the pharmacodynamic effects of morphine.

CONCLUSIONS

Itraconazole moderately increases plasma concentrations of oral morphine, probably by enhancing its absorption by inhibiting intestinal wall P-glycoprotein. A possible improvement of morphine penetration to the brain could not be observed.

Characterization of novel CYP2C8 haplotypes and their contribution to paclitaxel and repaglinide metabolism

Cytochrome P450 2C8 (CYP2C8) plays a major role in the metabolism of therapeutically important drugs which exhibit large interindividual differences in their pharmacokinetics. In order to evaluate any genetic influence on this variation, a CYP2C8 phenotype-genotype evaluation was carried out in Caucasians. Two novel CYP2C8 haplotypes, named B and C with frequencies of 24 and 22% in Caucasians, respectively, were identified and caused a significantly increased and reduced paclitaxel 6alpha-hydroxylation, respectively, as evident from analyses of 49 human liver samples. In healthy white subjects, CYP2C8*3 and the two novel haplotypes significantly influenced repaglinide pharmacokinetics in SLCO1B1c.521T/C heterozygous individuals: haplotype B was associated with reduced and haplotype C with increased repaglinide AUC (0-infinity). Functional studies suggested -271C>A (CYP2C8*1B) as a causative SNP in haplotype B. In conclusion, two novel common CYP2C8 haplotypes were identified and significantly associated with altered rate of CYP2C8-dependent drug metabolism in vitro and in vivo.

Developmental pharmacokinetics of ciclosporin--a population pharmacokinetic study in paediatric renal transplant candidates

AIMS

To use population pharmacokinetic modelling to characterize the influence of developmental and demographic factors on the pharmacokinetic variability of ciclosporin.

METHODS

Pharmacokinetic modelling was performed in NONMEM using a dataset comprising 162 pretransplant children, aged 0.36-17.5 years. Ciclosporin was given intravenously (3 mg kg(-1)) and orally (10 mg kg(-1)) on separate occasions followed by blood sampling for 24 h.

RESULTS

A three-compartment model with first-order absorption without lag-time best described the pharmacokinetics of ciclosporin. The most important covariate affecting systemic clearance (CL) and distribution volume (V) was body weight (BW; scaled allometrically), responsible for a fourfold difference in uncorrected ciclosporin CL and a sixfold difference in ciclosporin V. The other significant covariates, haematocrit, plasma cholesterol and creatinine, were estimated to explain 20-30% of interindividual differences in CL and V of ciclosporin. No age-related changes in oral bioavailability or in BW-normalized V were seen. The BW-normalized CL (CL/BW) declined with age and prepubertal children (<8 years) had an approximately 25% higher CL/BW than did older children. Normalization of CL for allometric BW (BW(3/4)) removed its relationship to age.

CONCLUSION

The relationship between CL and allometric BW is consistent with a gradual reduction in relative liver size, until adult values, and a relatively constant CYP3A4 content in the liver from about 6-12 months of age to adulthood. Ciclosporin oral bioavailability, known previously to display large interindividual variability, is not influenced by age. These findings can enable better individualization of ciclosporin dosing in infants, children and adolescents.

Effects of Daily Ingestion of Cranberry Juice on the Pharmacokinetics of Warfarin, Tizanidine, and Midazolam—Probes of CYP2C9, CYP1A2, and CYP3A4

Case reports suggest that cranberry juice can increase the anticoagulant effect of warfarin. We investigated the effects of cranberry juice on R-S-warfarin, tizanidine, and midazolam; probes of CYP2C9, CYP1A2, and CYP3A4. Ten healthy volunteers took 200 ml cranberry juice or water t.i.d. for 10 days. On day 5, they ingested 10 mg racemic R-S-warfarin, 1 mg tizanidine, and 0.5 mg midazolam, with juice or water, followed by monitoring of drug concentrations and thromboplastin time. Cranberry juice did not increase the peak plasma concentration or area under concentration-time curve (AUC) of the probe drugs or their metabolites, but slightly decreased (7%; P=0.051) the AUC of S-warfarin. Cranberry juice did not change the anticoagulant effect of warfarin. Daily ingestion of cranberry juice does not inhibit the activities of CYP2C9, CYP1A2, or CYP3A4. A pharmacokinetic mechanism for the cranberry juice-warfarin interaction seems unlikely.

Pharmacokinetics and bone effects of budesonide in primary biliary cirrhosis

BACKGROUND/AIM

To evaluate the safety of budesonide in primary biliary cirrhosis.

METHODS

77 primary biliary cirrhosis patients, with stages I-III at entry, were randomized to use either budesonide 6 mg and ursodeoxycholic acid 15 mg/kg (group A), or ursodeoxycholic acid alone (group B) daily for 3 years. In 22 patients, budesonide pharmacokinetics was determined after 3 years. Bone mass density was measured in 62 patients at baseline and 3 years; in 57 patients also liver biopsies were performed.

RESULTS

At 3 years, no significant differences in the pharmacokinetics of budesonide were found between the patients with stages 0-I, II and III primary biliary cirrhosis. In group A, bone mass density in femoral neck and lumbar spine were decreased by 3.6% (P = 0.0002) and 2.8% (P = 0.003) from the baseline. In group B, the corresponding decreases were 1.9% (P = 0.029) and 0.7% (P = 0.25), but the differences between the groups were not statistically significant (P = 0.16 for femoral neck and P = 0.08 for lumbar spine).

CONCLUSIONS

The plasma concentrations of budesonide do not significantly differ within stages I-III primary biliary cirrhosis patients. The combination of budesonide and ursodeoxycholic acid may decrease bone mass density in the femoral neck and lumbar spine in some primary biliary cirrhosis patients, and bone mass density is recommended to be monitored during budesonide therapy.

Gemfibrozil considerably increases the plasma concentrations of rosiglitazone

AIMS/HYPOTHESIS

Our aim was to investigate possible interaction between gemfibrozil and rosiglitazone, a thiazolidinedione antidiabetic drug.

METHODS

In a randomised crossover study with two phases, 10 healthy volunteers took 600 mg gemfibrozil or placebo orally twice daily for 4 days. On day 3, they ingested a single 4 mg dose of rosiglitazone. Plasma rosiglitazone and its N-desmethyl metabolite concentrations were measured for up to 48 h.

RESULTS

Gemfibrozil raised the mean area under the plasma rosiglitazone concentration-time curve (AUC) 2.3-fold (range 1.5- to 2.8-fold; p=0.00002) and prolonged the elimination half-life (t(1/2)) of rosiglitazone from 3.6 to 7.6 h ( p=0.000002). The peak plasma rosiglitazone concentration (C(max)) was increased only 1.2-fold (range 0.9- to 1.6-fold; p=0.01) by gemfibrozil, but gemfibrozil raised the plasma rosiglitazone concentration measured 24 h after dosing (C(24)) 9.8-fold (range, 4.5- to 33.6-fold; p=0.00008). In addition, gemfibrozil prolonged the t(max) of N-desmethylrosiglitazone from 7 to 12 h and reduced the N-desmethylrosiglitazone/rosiglitazone AUC(0-48) ratio by 38% ( p<0.01).

CONCLUSIONS/INTERPRETATION

Gemfibrozil raises the plasma concentrations of rosiglitazone probably by inhibiting the CYP2C8-mediated biotransformation of rosiglitazone. Co-administration of gemfibrozil, or another potent inhibitor of CYP2C8, and rosiglitazone could increase the efficacy but also the risk of concentration-dependent adverse effects of rosiglitazone.

Effects of gemfibrozil, itraconazole, and their combination on the pharmacokinetics and pharmacodynamics of repaglinide: potentially hazardous interaction between gemfibrozil and repaglinide

AIMS/HYPOTHESIS

Our aim was to investigate possible interactions of gemfibrozil, itraconazole, and their combination with repaglinide.

METHODS

In a randomised crossover study, 12 healthy volunteers received twice daily for 3 days either 600 mg gemfibrozil, 100 mg itraconazole (first dose 200 mg), both gemfibrozil and itraconazole, or placebo. On day 3 they ingested a 0.25 mg dose of repaglinide. Plasma drug and blood glucose concentrations were followed for 7 h and serum insulin and C-peptide concentrations for 3 h postdose.

RESULTS

Gemfibrozil raised the area under the plasma concentration-time curve (AUC) of repaglinide 8.1-fold (range 5.5- to 15.0-fold; p<0.001) and prolonged its half-life (t(1/2)) from 1.3 to 3.7 h (p<0.001). Although itraconazole alone raised repaglinide AUC only 1.4-fold (1.1- to 1.9-fold; p<0.001), the gemfibrozil-itraconazole combination raised it 19.4-fold (12.9- to 24.7-fold) and prolonged the t(1/2) of repaglinide to 6.1 h (p<0.001). Plasma repaglinide concentration at 7 h was increased 28.6-fold by gemfibrozil and 70.4-fold by the gemfibrozil-itraconazole combination (p<0.001). Gemfibrozil alone and in combination with itraconazole considerably enhanced and prolonged the blood glucose-lowering effect of repaglinide; i.e., repaglinide became a long-acting and stronger antidiabetic.

CONCLUSION/INTERPRETATION

Clinicians should be aware of this previously unrecognised and potentially hazardous interaction between gemfibrozil and repaglinide. Concomitant use of gemfibrozil and repaglinide is best avoided. If the combination is considered necessary, repaglinide dosage should be greatly reduced and blood glucose concentrations carefully monitored.

Elimination of the piperacillin/tazobactam combination during continuous venovenous haemofiltration and haemodiafiltration in patients with acute renal failure

The elimination of the piperacillin/tazobactam combination was studied in six patients with acute renal failure undergoing either continuous venovenous haemofiltration (CVVH) or continuous venovenous haemodiafiltration (CVVHDF) at 1 L/h and 2 L/h for 12 h. Piperacillin 4 g/tazobactam 0.5 g was given iv on three successive treatment periods and their concentrations in plasma, ultrafiltrate/dialysate and urine were determined for 12 h after each dose. The elimination half-life of piperacillin during CVVH (7.7 +/- 2.3 h; mean +/- s.d.) was significantly longer than during CVVHDF 1 L/h (6.7 +/- 1.9 h) or 2 L/h (6.1 +/- 2.0 h) (P< 0.05). Corresponding values for tazobactam were 13.9 +/- 3.9, 11.6 +/- 3.3 and 9.4 +/- 2.4 h, respectively (P< 0.05). Total piperacillin clearance during CVVH (3.89 +/- 1.23 L/h) was significantly lower than during CVVHDF 1 L/h (5.06 +/- 1.68 L/h) or 2 L/h (5.48 +/- 2.11 L/h) (P< 0.05). The corresponding tazobactam clearance values were 2.42 +/- 0.75, 3.13 +/- 0.66 and 3.75 +/- 1.43 L/h, respectively. The mean 12 h elimination of piperacillin and tazobactam in ultrafiltrate/dialysate was 29% and 37% during CVVH, 42% and 57% during CVVHDF (1 L/h), and 46% and 69% during CVVHDF (2 L/h). We recommend 8 hourly dosing of patients with renal failure on CVVH or CVVHDF with dialysis flow rates of 1 or 2 L/h treated with piperacillin 4 g/tazobactam 0.5 g.

Gemfibrozil is a potent inhibitor of human cytochrome P450 2C9

The in vitro inhibitory effects of gemfibrozil on cytochrome P450 (CYP) 1A2 (phenacetin O-deethylation), CYP2A6 (coumarin 7-hydroxylation), CYP2C9 (tolbutamide hydroxylation), CYP2C19 (S-mephenytoin 4'-hydroxylation), CYP2D6 (dextromethorphan O-deethylation), CYP2E1 (chlorzoxazone 6-hydroxylation), and CYP3A4 (midazolam 1'-hydroxylation) activities were examined using pooled human liver microsomes. The in vivo drug interactions of gemfibrozil were predicted in vitro using the [I]/([I] + K(i)) values. Gemfibrozil strongly and competitively inhibited CYP2C9 activity, with a K(i) (IC(50)) value of 5.8 (9.6) microM. In addition, gemfibrozil exhibited somewhat smaller inhibitory effects on CYP2C19 and CYP1A2 activities, with K(i) (IC(50)) values of 24 (47) microM and 82 (136) microM, respectively. With concentrations up to 250 microM, gemfibrozil showed no appreciable effect on CYP2A6, CYP2D6, CYP2E1, and CYP3A4 activities. Based on [I]/([I] + K(i)) values calculated using peak total (or unbound) plasma concentration of gemfibrozil, 96% (56%), 86% (24%), and 64% (8%) inhibition of the clearance of CYP2C9, CYP2C19, and CYP1A2 substrates could be expected, respectively. In conclusion, gemfibrozil inhibits the activity of CYP2C9 at clinically relevant concentrations, and this is the likely mechanism by which gemfibrozil interacts with CYP2C9 substrate drugs, such as warfarin and glyburide. Gemfibrozil may also impair clearance of CYP2C19 and CYP1A2 substrates, but inhibition of other CYP isoforms is unlikely.

In vitro evaluation of valproic acid as an inhibitor of human cytochrome P450 isoforms: preferential inhibition of cytochrome P450 2C9 (CYP2C9)

AIMS

To evaluate the potency and specificity of valproic acid as an inhibitor of the activity of different human CYP isoforms in liver microsomes.

METHODS

Using pooled human liver microsomes, the effects of valproic acid on seven CYP isoform specific marker reactions were measured: phenacetin O-deethylase (CYP1A2), coumarin 7-hydroxylase (CYP2A6), tolbutamide hydroxylase (CYP2C9), S-mephenytoin 4'-hydroxylase (CYP2C19), dextromethorphan O-demethylase (CYP2D6), chlorzoxazone 6-hydroxylase (CYP2E1) and midazolam 1'-hydroxylase (CYP3A4).

RESULTS

Valproic acid competitively inhibited CYP2C9 activity with a Ki value of 600 microM. In addition, valproic acid slightly inhibited CYP2C19 activity (Ki = 8553 microM, mixed inhibition) and CYP3A4 activity (Ki = 7975 microM, competitive inhibition). The inhibition of CYP2A6 activity by valproic acid was time-, concentration- and NADPH-dependent (KI = 9150 microM, Kinact=0.048 min(-1)), consistent with mechanism-based inhibition of CYP2A6. However, minimal inhibition of CYP1A2, CYP2D6 and CYP2E1 activities was observed.

CONCLUSIONS

Valproic acid inhibits the activity of CYP2C9 at clinically relevant concentrations in human liver microsomes. Inhibition of CYP2C9 can explain some of the effects of valproic acid on the pharmacokinetics of other drugs, such as phenytoin. Co-administration of high doses of valproic acid with drugs that are primarily metabolized by CYP2C9 may result in significant drug interactions.

Stereoselective pharmacokinetics of cisapride in healthy volunteers and the effect of repeated administration of grapefruit juice

AIMS

To determine whether the pharmacokinetics of cisapride and its interaction with grapefruit juice are stereoselective.

METHODS

The study was a randomized, two-phase cross over design with a washout period of 2 weeks. Ten healthy volunteers were pretreated with either water or 200 ml double strength grapefruit juice three times a day for 2 days. On the 3rd each subject ingested a single 10 mg dose of rac-cisapride tablet. Double strength grapefruit juice (200 ml) or water was administered during cisapride dosing and 0.5 and 1.5 h thereafter. Blood samples were collected before and for 32 h after cisapride administration. Plasma concentrations of cisapride enantiomers were measured by a chiral h.p.l.c. method. A standard 12-lead ECG was recorded before cisapride administration (baseline) and 2, 5, 8, and 12 h later.

RESULTS

This study showed that cisapride pharmacokinetics are stereoselective. In control (water treated) subjects, the mean Cmax (30 +/- 13.6 ng ml-1; P = 0.0008) and AUC(0, infinity) (201 +/- 161 ng ml-1 h; P = 0.029) of (-)-cisapride were significantly higher than the Cmax (10.5 +/- 3.4 ng ml-1) and AUC(0, infinity) (70 +/- 51.5 ng ml-1 h) of (+)-cisapride. There was no marked difference in elimination half-life between (-)-cisapride (4.7 +/- 2.7 h) and (+)-cisapride (4.8 +/- 3 h). Compared with the water treated group, grapefruit juice significantly increased the mean Cmax of (-)-cisapride from 30 +/- 13.6-55.5 +/- 18 ng ml-1 (95% CI on mean difference, -33, -17; P = 0.00005) and of (+)-cisapride from 10.5 +/- 3.4 to 18.4 +/- 6.2 ng ml-1 (95% CI on mean difference, -11.8, -3.9, P = 0.00015). The mean AUC(0, infinity) of (-)-cisapride was increased from 201 +/- 161 to 521.6 +/- 303 ng ml-1 h (95% CI on mean difference, -439, -202; P = 0.0002) and that of (+)-cisapride from 70 +/- 51.5 to 170 +/- 91 ng ml-1 h (95% CI on mean difference, -143, -53; P = 0.0005). The tmax was also significantly increased for both enantiomers (from 1.35 to 2.8 h for (-)-cisapride and from 1.75 to 2.9 h for (+)-cisapride in the control and grapefruit juice group, respectively; P < 0.05). The t(1/2) of (-)-cisapride was significantly increased by grapefruit juice, while this change did not reach significant level for (+)-cisapride. The proportion of pharmacokinetic changes brought about by grapefruit juice was similar for both enantiomers, suggesting non-stereoselective interaction. We found no significant difference in mean QTc intervals between the water and grapefruit juice treated groups.

CONCLUSIONS

The pharmacokinetics of cisapride is stereoselective. Grapefruit juice elevates plasma concentrations of both (-)- and (+)-cisapride, probably through inhibition of CYP3A in the intestine. At present, there are no data on whether the enantiomers exhibit stereoselective pharmacodynamic actions. If they do, determination of plasma concentrations of the individual enantiomers as opposed to those of racemic cisapride may better predict the degree of drug interaction, cardiac safety and prokinetic efficacy of cisapride.

Effect of methylprednisolone on CYP3A4-mediated drug metabolism in vivo

OBJECTIVE

To study the effects of methylprednisolone on the pharmacokinetics and pharmacodynamics of triazolam.

METHODS

In this three-phase cross-over study, ten healthy subjects received 0.25 mg oral triazolam on three occasions: on day 1 (no pretreatment, control), on day 8 (1 h after a single dose of 32 mg oral methylprednisolone) and on day 18 (after further treatment with 8 mg oral methylprednisolone daily for 9 days). The plasma concentrations of triazolam were determined up to 10 h, and its effects were measured using four psychomotor tests up to 6 h.

RESULTS

The single dose of methylprednisolone showed no significant effects on the pharmacokinetics of triazolam. However, the Digit Symbol Substitution Test result was better (P < 0.05) during the single-dose methylprednisolone phase than during the control phase, the other three tests showing no differences between the phases. The multiple-dose treatment with methylprednisolone reduced the mean peak plasma concentration (Cmax) of triazolam by 30% (P < 0.05) but had no significant effects on the time to Cmax (tmax), elimination half-life (t 1/2), area under the plasma concentration-time curve from 0 h to 10 h (AUC(0-10 h)) and AUC(0-infinity) and did not alter the effects of triazolam.

CONCLUSION

A single, relatively high dose of methylprednisolone (32 mg) did not affect cytochrome P450 (CYP)3A4 activity, and treatment with 8 mg methylprednisolone daily for 9 days did not result in clinically significant induction of CYP3A4.

Effects of rifampin on the pharmacokinetics and pharmacodynamics of glyburide and glipizide

OBJECTIVE

To study the effects of rifampin (INN, rifampicin) on the pharmacokinetics and pharmacodynamics of glyburide (INN, glibenclamide) and glipizide, 2 sulfonylurea antidiabetic drugs.

METHODS

Two separate, randomized, 2-phase, crossover studies with an identical design were conducted. In each study, 10 healthy volunteers received 600 mg rifampin or placebo once daily for 5 days. On day 6, a single dose of 1.75 mg glyburide (study I) or 2.5 mg glipizide (study II) was administered orally. Plasma glyburide and glipizide and blood glucose concentrations were measured for 12 hours.

RESULTS

In study I, rifampin decreased the area under the plasma concentration--time curve [AUC(0-infinity)] of glyburide by 39% (P <.001) and the peak plasma concentration by 22% (P =.01). The elimination half-life of glyburide was shortened from 2.0 to 1.7 hours (P <.05) by rifampin. The blood glucose decremental AUC(0-7) (net area below baseline) and the maximum decrease in the blood glucose concentration were decreased by 44% (P =.05) and 36% (P <.001), respectively, by rifampin. In study II, rifampin decreased the AUC(0-infinity) of glipizide by 22% (P <.05) and shortened its half-life from 3.0 to 1.9 hours (P =.01). No statistically significant differences in the blood glucose concentrations were found between the phases; however, 4 subjects had moderate hypoglycemia during the placebo phase but only 1 subject had moderate hypoglycemia during the rifampin phase.

CONCLUSIONS

Rifampin moderately decreased the plasma concentrations and effects of glyburide but had only a slight effect on glipizide. The mechanism underlying the interaction between rifampin and glyburide is probably induction of either CYP2C9 or P-glycoprotein or both. Induction of CYP2C9 would explain the increased systemic elimination of glipizide. It is probable that the blood glucose--lowering effect of glyburide is reduced during concomitant treatment with rifampin. In some patients, the effects of glipizide may also be reduced by rifampin.

Plasma concentrations of active lovastatin acid are markedly increased by gemfibrozil but not by bezafibrate

BACKGROUND

Concomitant use of fibrates with statins has been associated with an increased risk of myopathy, but the underlying mechanism of this adverse reaction remains unclear. Our aim was to study the effects of bezafibrate and gemfibrozil on the pharmacokinetics of lovastatin.

METHODS

This was a randomized, double-blind, 3-phase crossover study. Eleven healthy volunteers took 400 mg/day bezafibrate, 1200 mg/day gemfibrozil, or placebo for 3 days. On day 3, each subject ingested a single 40 mg dose of lovastatin. Plasma concentrations of lovastatin, lovastatin acid, gemfibrozil, and bezafibrate were measured up to 24 hours.

RESULTS

Gemfibrozil markedly increased the plasma concentrations of lovastatin acid, without affecting those of the parent lovastatin compared with placebo. During the gemfibrozil phase, the mean area under the plasma concentration-time curve from 0 to 24 hours [AUC(0-24)] of lovastatin acid was 280% (range, 131% to 1184%; P < .001) and the peak plasma concentration (Cmax) was 280% (range, 123% to 1042%; P < .05) of the corresponding value during the placebo phase. Bezafibrate had no statistically significant effect on the AUC(0-24) or Cmax of lovastatin or lovastatin acid compared with placebo.

CONCLUSIONS

Gemfibrozil markedly increases plasma concentrations of lovastatin acid, but bezafibrate does not. The increased risk of myopathy observed during concomitant treatment with statins and fibrates may be partially of a pharmacokinetic origin. The risk of developing myopathy during concomitant therapy with lovastatin and a fibrate may be smaller with bezafibrate than with gemfibrozil.

Effects of fluconazole and fluvoxamine on the pharmacokinetics and pharmacodynamics of glimepiride

OBJECTIVE

Our objective was to study the effects of fluconazole and fluvoxamine on the pharmacokinetics and pharmacodynamics of glimepiride, a new sulfonylurea antidiabetic drug.

METHODS

In this randomized, double-blind, three-phase crossover study, 12 healthy volunteers took 200 mg of fluconazole once daily (400 mg on day 1), 100 mg of fluvoxamine once daily, or placebo once daily for 4 days. On day 4, a single oral dose of 0.5 mg of glimepiride was administered. Plasma glimepiride and blood glucose concentrations were measured up to 12 hours.

RESULTS

In the fluconazole phase, the mean total area under the plasma concentration-time curve of glimepiride was 238% (P <.0001) and the peak plasma concentration was 151% (P <.0001) of the respective control value. The mean elimination half-life of glimepiride was prolonged from 2.0 to 3.3 hours (P <.0001) by fluconazole. In the fluvoxamine phase, the mean area under the plasma concentration-time curve of glimepiride was not significantly different from that in the placebo phase. However, the mean peak plasma concentration of glimepiride was 143% (P <.05) of the control and the elimination half-life was prolonged from 2.0 to 2.3 hours (P <.01) by fluvoxamine. Fluconazole and fluvoxamine did not cause statistically significant changes in the effects of glimepiride on blood glucose concentrations.

CONCLUSIONS

Fluconazole considerably increased the area under the plasma concentration-time curve of glimepiride and prolonged its elimination half-life. This was probably caused by inhibition of the cytochrome P-450 2C9-mediated biotransformation of glimepiride by fluconazole. Concomitant use of fluconazole with glimepiride may increase the risk of hypoglycemia as much as would a 2- to 3-fold increase in the dose of glimepiride. Fluvoxamine moderately increased the plasma concentrations and slightly prolonged the elimination half-life of glimepiride.

Selegiline pharmacokinetics are unaffected by the CYP3A4 inhibitor itraconazole

OBJECTIVE

To characterise the effects of itraconazole, a potent inhibitor of CYP3A4, on the pharmacokinetics of selegiline in healthy volunteers.

METHODS

In this randomised, placebo-controlled crossover study with two phases, 12 healthy volunteers took either 200 mg itraconazole or matched placebo once daily for 4 days. On day 4, a single 10-mg oral dose of selegiline hydrochloride was administered. Serum concentrations of selegiline and its primary metabolites desmethylselegiline and l-methamphetamine were determined up to 32 h. A caffeine test was performed on day 3 of both phases, by measuring the plasma paraxanthine/caffeine concentration ratio 6 h after caffeine intake, to examine the role of CYP1A2 in selegiline pharmacokinetics. In addition, the effects of itraconazole on the metabolism of selegiline in vitro were characterised by using human liver microsomes.

RESULTS

Itraconazole had no significant effects on the pharmacokinetic variables of selegiline, desmethylselegiline or l-methamphetamine, with the exception that the AUC of desmethylselegiline was increased by about 10% (P < 0.05). There was a significant correlation between the AUC(desmethylselegiline)/AUC(selegiline) ratio and the paraxanthine/caffeine ratio (r = 0.41; P < 0.05), suggesting involvement of CYP1A2 in the formation of desmethylselegiline. In experiments with human liver microsomes, itraconazole had no inhibitory effect on the formation of either desmethylselegiline or l-methamphetamine from selegiline.

CONCLUSIONS

The pharmacokinetics of selegiline in healthy volunteers were unaffected by the potent CYP3A4 inhibitor itraconazole. In addition, itraconazole showed no inhibitory effect on the biotransformation of selegiline to desmethylselegiline and l-methamphetamine by human liver microsomes. These findings suggest that selegiline is not susceptible to interaction with CYP3A4 inhibitors.

Rifampin greatly reduces plasma simvastatin and simvastatin acid concentrations

BACKGROUND

Rifampin (rifampicin) is a potent inducer of several cytochrome P450 (CYP) enzymes, including CYP3A4. The cholesterol-lowering drug simvastatin has an extensive first-pass metabolism, and it is partially metabolized by CYP3A4. This study was conducted to investigate the effect of rifampin on the pharmacokinetics of simvastatin.

METHODS

In a randomized cross-over study with two phases and a washout of 4 weeks, 10 healthy volunteers received a 5-day pretreatment with rifampin (600 mg daily) or placebo. On day 6, a single 40-mg dose of simvastatin was administered orally. Plasma concentrations of simvastatin and its active metabolite simvastatin acid were measured up to 12 hours with a sensitive liquid chromatography-ion spray tandem mass spectrometry method.

RESULTS

Rifampin decreased the total area under the plasma concentration-time curve of simvastatin and simvastatin acid by 87% (P < .001) and 93% (P < .001), respectively. Also the peak concentrations of both simvastatin and simvastatin acid were reduced greatly (by 90%) by rifampin (P < .001). On the other hand, rifampin had no significant effect on the elimination half-life of simvastatin or simvastatin acid.

CONCLUSIONS

Rifampin greatly decreases the plasma concentrations of simvastatin and simvastatin acid. Because the elimination half-life of simvastatin was not affected by rifampin, induction of the CYP3A4-mediated first-pass metabolism of simvastatin in the intestine and the liver probably explains this interaction. Concomitant use of potent inducers of CYP3A4 can lead to a considerably reduced cholesterol-lowering efficacy of simvastatin.

Effect of rifampicin on the pharmacokinetics and pharmacodynamics of glimepiride

AIMS

To study the effects of rifampicin on the pharmacokinetics and pharmaco-dynamics of glimepiride, a new sulphonylurea antidiabetic drug.

METHODS

In this randomised, two-phase cross-over study, 10 healthy volunteers were treated for 5 days with 600 mg rifampicin or placebo once daily. On day 6, a single oral dose of 1 mg glimepiride was administered. Plasma glimepiride and blood glucose concentrations were measured up to 12 h.

RESULTS

Rifampicin decreased the mean area under the plasma concentration-time curve of glimepiride by 34% (P < 0.001) and the mean elimination half-life by 25% (P < 0.05). No significant differences in the blood glucose response to glimepiride were observed between the placebo and rifampicin phases. However, symptomatic hypoglycaemia occurred only during the placebo phase.

CONCLUSIONS

The effects of rifampicin on the pharmacokinetics of glimepiride suggest that rifampicin induced the CYP2C9-mediated metabolism of glimepiride and thereby slightly increased its systemic clearance. Because the interaction was modest and did not significantly alter the glucose-lowering effect of glimepiride in healthy volunteers, it is probably of limited clinical significance. However, in some patients the hypoglycaemic effect of glimepiride may be reduced during concomitant treatment with rifampicin.

Rifampin decreases the plasma concentrations and effects of repaglinide

OBJECTIVE

To study the effects of rifampin (INN, rifampicin) on the pharmacokinetics and pharmacodynamics of repaglinide, a new short-acting antidiabetic drug.

METHODS

In a randomized, two-phase crossover study, nine healthy volunteers were given a 5-day pretreatment with 600 mg rifampin or matched placebo once daily. On day 6 a single 0.5-mg dose of repaglinide was administered. Plasma repaglinide and blood glucose concentrations were measured up to 7 hours.

RESULTS

Rifampin decreased the total area under the concentration-time curve of repaglinide by 57% (P < .001) and the peak plasma repaglinide concentration by 41% (P = .001). The elimination half-life of repaglinide was shortened from 1.5 to 1.1 hours (P < .01). The blood glucose decremental area under the concentration-time curve from 0 to 3 hours was reduced from 0.94 to -0.23 mmol/L x h (P < .05), and the maximum decrease in blood glucose concentration from 1.6 to 1.0 mmol/L (P < .05) by rifampin.

CONCLUSIONS

Rifampin considerably decreases the plasma concentrations of repaglinide and also reduces its effects. This interaction is probably caused by induction of the CYP3A4-mediated metabolism of repaglinide. It is probable that the effects of repaglinide are decreased during treatment with rifampin or other potent inducers of CYP3A4, such as carbamazepine, phenytoin, or St John's wort.

The cytochrome P450 3A4 inhibitor itraconazole markedly increases the plasma concentrations of dexamethasone and enhances its adrenal-suppressant effect

OBJECTIVE

To examine the possible interaction of itraconazole with orally and intravenously administered dexamethasone.

METHODS

In a randomized, double-blind, placebo-controlled crossover study with four phases, eight healthy subjects took either 200 mg itraconazole (in two phases) or placebo (in two phases) orally once daily for 4 days. On day 4 each subject received an oral dose of 4.5 mg dexamethasone or an intravenous dose of 5.0 mg dexamethasone sodium phosphate during both itraconazole and placebo phases. Plasma dexamethasone and cortisol concentrations were determined by HPLC up to 71 hours, itraconazole and hydroxyitraconazole up to 23 hours.

RESULTS

Itraconazole decreased the systemic clearance of intravenously administered dexamethasone by 68% (P < .001), increased the total area under the plasma dexamethasone concentration-time curve [AUC(0-infinity)] 3.3-fold (P < .001), and prolonged the elimination half-life of dexamethasone 3.2-fold (P < .001). The AUC(0-infinity) of oral dexamethasone was increased 3.7-fold (P < .001), the peak plasma concentration 1.7-fold (P < .001), and the elimination half-life 2.8-fold (P < .001) by itraconazole. The morning plasma cortisol concentrations measured 47 and 71 hours after administration of dexamethasone were substantially lower after exposure to itraconazole than to placebo (P < .001). Accordingly, the adrenal-suppressant effect of dexamethasone was greatly enhanced during the itraconazole phases.

CONCLUSIONS

Itraconazole markedly increases the systemic exposure to and effects of dexamethasone. A careful follow-up is recommended when itraconazole or other potent inhibitors of the cytochrome P450 3A4 are added to the drug regimen of patients receiving dexamethasone.

Effects of metronidazole on midazolam metabolism in vitro and in vivo

OBJECTIVE

Case reports have described elevated concentrations of CYP3A4 substrates (e.g. cyclosporin) during metronidazole treatment. Therefore, we wanted to study whether metronidazole affects CYP3A4 activity, using midazolam as a model substrate in vitro and in vivo.

METHODS

In the in vitro part of the study, the effects of various concentrations of metronidazole (0-500 microM) on the formation of 1'-hydroxymidazolam from midazolam were studied using human liver microsomal preparations (n = 4). In the in vivo part, the effects of metronidazole on the pharmacokinetics and pharmacodynamics of oral midazolam were evaluated in a randomised, placebo-controlled cross-over study in ten healthy subjects. The subjects took either 400 mg metronidazole or matched placebo orally twice daily for 3 days. On day 3, 15 mg midazolam was administered orally. Plasma concentrations of midazolam and 1'-hydroxymidazolam were determined up to 24 h. The effects of midazolam were measured up to 10 h.

RESULTS

Metronidazole (10-500 microM) showed no inhibitory effect on 1'-hydroxymidazolam formation by human liver microsomes. In healthy volunteers, metronidazole had no statistically significant effects on the pharmacokinetics of midazolam and 1'-hydroxymidazolam, and also the ratio of 1'-hydroxymidazolam to midazolam in plasma remained unchanged by metronidazole. The four employed psychomotor tests did not show significant differences between the metronidazole and placebo phases.

CONCLUSION

Metronidazole had no effects on the 1'-hydroxylation of midazolam in vitro or on the pharmacokinetics and pharmacodynamics of midazolam in vivo. These findings indicate that metronidazole is not an inhibitor of CYP3A4.

Involvement of CYP1A2 and CYP3A4 in lidocaine N-deethylation and 3-hydroxylation in humans

The roles of cytochrome P-450 (CYP) enzymes in the N-deethylation, i.e., formation of monoethylglycinexylidide (MEGX), and 3-hydroxylation of lidocaine were studied with human liver microsomes and recombinant human CYP isoforms. Both CYP1A2 and CYP3A4 were found to be capable of catalyzing the formation of MEGX and 3-OH-lidocaine. Lidocaine N-deethylation by liver microsomes was strongly inhibited by furafylline (by about 60%) and anti-CYP1A1/2 antibodies (>75%) at 5 microM lidocaine, suggesting that CYP1A2 was the major isoform catalyzing lidocaine N-deethylation at low (therapeutically relevant) lidocaine concentrations. Troleandomycin inhibited the N-deethylation of lidocaine by about 50% at 800 microM lidocaine, suggesting that the role of CYP3A4 may be more important than that of CYP1A2 at high lidocaine concentrations. Chemical inhibition and immunoinhibition studies also indicated that 3-OH-lidocaine formation was catalyzed almost exclusively by CYP1A2, CYP3A4 playing only a minor role. Although the CYP2C9 inhibitor sulfaphenazole (100 microM) inhibited MEGX formation by about 30%, recombinant human CYP2C9 showed very low catalytic activity, suggesting a negligible role for this enzyme in lidocaine N-deethylation. Chemical inhibition studies indicated that CYP2C19, CYP2D6, and CYP2E1 did not play significant roles in the metabolism of lidocaine in vitro. Taken together, these results demonstrate that CYP1A2 and CYP3A4 enzymes are the major CYP isoforms involved in lidocaine N-deethylation. Therefore, the MEGX test (formation of MEGX from lidocaine) is not a suitable marker of hepatic CYP3A4 activity in vivo.

Effect of grapefruit juice dose on grapefruit juice-triazolam interaction: repeated consumption prolongs triazolam half-life

OBJECTIVE

Grapefruit juice inhibits CYP3A4-mediated metabolism of several drugs during first pass. In this study, the effect of grapefruit juice dose on the extent of grapefruit juice-triazolam interaction was investigated.

METHODS

In a randomised, four-phase, crossover study, 12 healthy volunteers received 0.25 mg triazolam with water, with 200 ml normal-strength or double-strength grapefruit juice or, on the third day of multiple-dose [three times daily (t.i.d.)] administration of double-strength grapefruit juice. Timed blood samples were collected up to 23 h after dosing, and the effects of triazolam were measured with four psychomotor tests up to 10 h after dosing.

RESULTS

The area under the plasma triazolam concentration time curve (AUC(0-infinity)) was increased by 53% (P < 0.01), 49% (P < 0.01) and 143% (P < 0.001) by a single dose of normal-strength, a single dose of double-strength and multiple-dose administration of double-strength grapefruit juice, respectively. The peak plasma concentration (Cmax) of triazolam was increased by about 40% by a single dose of normal-strength grapefruit juice (P < 0.01) and multiple-dose grapefruit juice (P < 0.01) and by 25% by a single dose of double-strength grapefruit juice (P < 0.05). The elimination half-life (t(1/2)) of triazolam was prolonged by 54% during the multiple-dose grapefruit juice phase (P < 0.001). A significant increase in the pharmacodynamic effects of triazolam was seen during the multiple-dose grapefruit juice phase in the digit symbol substitution test (DSST, P < 0.05), in subjective overall drug effect (P < 0.05) and in subjective drowsiness (P < 0.05).

CONCLUSIONS

Even one glass of grapefruit juice increases plasma triazolam concentrations, but repeated consumption of grapefruit juice produces a significantly greater increase in triazolam concentrations than one glass of juice. The t(1/2) of triazolam is prolonged by repeated consumption of grapefruit juice, probably due to inhibition of hepatic CYP3A4 activity.

Plasma concentrations of active simvastatin acid are increased by gemfibrozil

BACKGROUND

Concomitant treatment with simvastatin and gemfibrozil, two lipid-lowering drugs, has been associated with occurrence of myopathy in case reports. The aim of this study was to determine whether gemfibrozil affects the pharmacokinetics of simvastatin and whether it affects CYP3A4 activity in vitro.

METHODS

A double-blind, randomized crossover study with two phases (placebo and gemfibrozil) was carried out. Ten healthy volunteers were given gemfibrozil (600 mg twice daily) or placebo orally for 3 days. On day 3 they ingested a single 40-mg dose of simvastatin. Plasma concentrations of simvastatin and simvastatin acid were measured up to 12 hours. In addition, the effect of gemfibrozil (0 to 1,200 micromol/L) on midazolam 1'-hydroxylation, a CYP3A4 model reaction, was investigated in human liver microsomes in vitro.

RESULTS

Gemfibrozil increased the mean total area under the plasma concentration-time curve of simvastatin [AUC(0-infinity)] by 35% (P < .01) and the AUC(0-infinity) of simvastatin acid by 185% (P < .001). The elimination half-life of simvastatin was increased by 74% (P < .05), and that of simvastatin acid was increased by 51% (P < .01) by gemfibrozil. The peak concentration of simvastatin acid was increased by 112%, from 3.20 +/- 2.73 ng/mL to 6.78 +/- 4.67 ng/mL (mean +/- SD; P < .01). In vitro, gemfibrozil showed no inhibition of midazolam 1'-hydroxylation.

CONCLUSIONS

Gemfibrozil increases plasma concentrations of simvastatin and, in particular, its active form, simvastatin acid, suggesting that the increased risk of myopathy in combination treatment is, at least partially, of a pharmacokinetic origin. Because gemfibrozil does not inhibit CYP3A4 in vitro, the mechanism of the pharmacokinetic interaction is probably inhibition of non-CYP3A4-mediated metabolism of simvastatin acid.

Effect of fluconazole on plasma fluvastatin and pravastatin concentrations

OBJECTIVE

To study the effects of fluconazole on the pharmacokinetics of fluvastatin and pravastatin, two inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase.

METHODS

Two separate randomised, double-blind, two-phase, crossover studies with identical study design were carried out. In each study, 12 healthy volunteers were given a 4-day pretreatment with oral fluconazole (400 mg on day 1 and 200 mg on days 2-4) or placebo, according to a randomisation schedule. On day 4, a single oral dose of 40 mg fluvastatin (study I) or 40 mg pravastatin (study II) was administered orally. Plasma concentrations of fluvastatin, pravastatin and fluconazole were measured over 24 h.

RESULTS

In study 1, fluconazole increased the mean area under the plasma fluvastatin concentration-time curve (AUC0-infinity) by 84% (P < 0.01), the mean elimination half-life (t1/2) of fluvastatin by 80% (P < 0.01) and its mean peak plasma concentration (Cmax) by 44% (P < 0.05). In study II, fluconazole had no significant effect on the pharmacokinetics of pravastatin.

CONCLUSIONS

Fluconazole has a significant interaction with fluvastatin. The mechanism of the increased plasma concentrations and prolonged elimination of fluvastatin is probably inhibition of the CYP2C9-mediated metabolism of fluvastatin by fluconazole. Care should be taken if fluconazole or other potent inhibitors of CYP2C9 are prescribed to patients using fluvastatin. However, pravastatin is not susceptible to interactions with fluconazole or other potent CYP2C9 inhibitors.

Elimination of meropenem during continuous veno-venous haemofiltration and haemodiafiltration in patients with acute renal failure

Meropenem elimination was studied in six patients with acute renal failure on continuous venovenous haemofiltration (CVVH) or continuous veno-venous haemodiafiltration (CVVHDF) 1 L/h and 2 L/h for 12 h. Meropenem 1 g was given iv over three dialysis periods, and plasma, ultrafiltrate/dialysate and urine concentrations of meropenem were determined. The half-life of meropenem was significantly longer (P < 0.05) during CVVH (7.5 +/- 2.0 h; mean +/- S.D.) than during CVVHDF 1 L/h (5.6 +/- 1.4 h) or 2 L/h (4.8 +/- 1.2 h). Meropenem clearance was 3.27 +/- 2.30 L/h, 4.72 +/- 2.69 L/h and 5.71 +/- 3.58 L/h in CVVH, CVVHDF 1 L/h and CVVHDF 2 L/h, respectively (P < 0.05 between CVVH and CVVHDF). Patients with renal failure on CVVHDF 1 or 2 L/h should be treated with meropenem 1 g bid; 500 mg tid may be enough for patients on CVVH.

Lack of correlation between in vitro and in vivo studies on the effects of tangeretin and tangerine juice on midazolam hydroxylation

BACKGROUND

Tangeretin is a flavonoid that stimulates the catalytic activity of cytochrome P450 3A4 (CYP3A4) and is found in high levels in tangerine juice.

METHODS

The effect of tangeretin on hydroxylation of midazolam, a CYP3A4 probe, was examined in vitro with human liver microsomes and recombinant CYP3A4. In addition, the effect of tangerine juice on the pharmacokinetics and pharmacodynamics of orally administered midazolam (15 mg) and its active 1'-hydroxymetabolite was studied in a randomized crossover study in eight healthy volunteers.

RESULTS

In microsomes from three human livers, tangeretin (1 to 100 micromol/L) increased 1'-hydroxymidazolam formation (12.5 micromol/L midazolam) by up to 212%. In complementary deoxyribonucleic acid-expressed CYP3A4, a 52% stimulation of midazolam 1'-hydroxylation was reached at 50 micromol/L tangeretin with no effect on midazolam 4-hydroxylation. In the pharmacokinetic-pharmacodynamic study, 200 mL tangerine juice reduced the area under the concentration versus time curve to 1.5 hours [AUC(O-1.5h)] of midazolam and 1'-hydroxymidazolam by 39% and 46%, respectively, and prolonged the time to reach peak concentration (P < .05) without affecting the total AUC values, elimination half-life values, or AUC ratios (1'-hydroxymidazolam/midazolam). These findings are consistent with a small delay in the absorption of midazolam and lack of effect on midazolam 1'-hydroxylation. Accordingly, tangerine juice slightly postponed the maximum pharmacodynamic effects of midazolam (P < .05).

CONCLUSION

Tangeretin is a potent regioselective stimulator of midazolam 1'-hydroxylation by human liver microsomes and complementary deoxyribonucleic acid-expressed CYP3A4. However, tangerine juice is unlikely to have any appreciable effect on CYP3A4 in humans. Further studies are required to assess whether in vitro stimulators of CYP3A4 can influence drug metabolism in vivo.

Diltiazem and mibefradil increase the plasma concentrations and greatly enhance the adrenal-suppressant effect of oral methylprednisolone

OBJECTIVE

To examine the possible interaction of the calcium channel blockers diltiazem and mibefradil with orally administered methylprednisolone.

METHODS

In this randomized, double-blind, placebo-controlled, three-phase crossover study, nine healthy SUBJECTS received 60 mg diltiazem three times a day, 50 mg mibefradil once a day, or placebo orally for 3 days. On day 3, each subject received a 16-mg oral dose of methylprednisolone. Plasma concentrations of methylprednisolone and cortisol were determined by HPLC up to 47 hours.

RESULTS

Compared with placebo, diltiazem and mibefradil increased the total area under the plasma concentration-time curve of methylprednisolone [AUC(0-infinity)] 2.6-fold (P < .001) and 3.8-fold (P < .001), the peak plasma concentration 1.6-fold (P < .001) and 1.8-fold (P < .001), and the elimination half-life 1.9-fold (P < .001) and 2.7-fold (P < .001), respectively. The nighttime exposure to methylprednisolone [AUC(12-23)] was increased 28.2-fold (P < .01) and 72.1-fold (P < .001) by diltiazem and mibefradil, respectively, and correlated negatively (r = -0.81, P < .001) with the morning plasma cortisol concentration (measured at 8 AM, 23 hours after the administration of methylprednisolone). During the diltiazem phase, the morning plasma cortisol concentration was 12% of that during the placebo phase (P < .001); during the mibefradil phase, the morning plasma cortisol concentration was 2% of that during the placebo phase (P < .001).

CONCLUSIONS

Coadministration of diltiazem or mibefradil with methylprednisolone resulted in increased plasma concentrations and a greatly enhanced adrenal-suppressant effect of oral methylprednisolone. Care should be taken if methylprednisolone is coadministered with a potent CYP3A4 inhibitor for a long period.

Platelet dysfunction after intravenous ketorolac or propacetamol

BACKGROUND

Paracetamol is a weak cyclo-oxygenase inhibitor in vitro. A recent study in children has shown that high doses of paracetamol are effective and safe. We studied the effect of propacetamol on haemostasis in adult volunteers.

METHODS

Ten volunteers were investigated in a double-blind, randomized, crossover study. They received propacetamol 60 mg kg(-1) or ketorolac 0.4 mg kg(-1) in saline i.v. (30 min) in two different sessions. Platelet function was evaluated before the test infusion (S-0), two (S-2) and 24 h (S-24) after the start of the infusion. Coagulation parameters (PT, APTT, factor V and VII activities) were measured at S-0, S-24 and 48 h (S-48).

RESULTS

One of the volunteers had no secondary platelet aggregation in S-0 and was excluded from the final analysis. Two hours (S-2) after propacetamol and ketorolac administration the adrenaline (0.9 microg ml(-1) and 9.0 microg ml(-1)) induced maximal platelet aggregation was decreased compared with S-0. At S-2 platelet aggregation was inhibited more after ketorolac than after propacetamol. At 24 h after ketorolac, but not after propacetamol, there was still a decrease in the adrenaline-induced maximal platelet aggregation. Propacetamol did not affect adenosine diphosphate (ADP)-induced maximal platelet aggregation, whereas ketorolac decreased 3 and 6 microM ADP-induced maximal platelet aggregation at S-2 and S-24. However, 2 h after both ketorolac and propacetamol, thromboxane B2 (TxB2) concentration decreased in platelet rich plasma after 5 min aggregation induced by 8 microM ADP. Coagulation was unaffected.

CONCLUSION

Propacetamol 60 mg kg(-1) i.v. causes reversible platelet dysfunction demonstrated by a decrease in maximal platelet aggregation and TxB2 concentration. After 0.4 mg kg(-1) ketorolac i.v. platelet aggregation and TxB2 formation are inhibited more in comparison with propacetamol, and platelet dysfunction is still seen after 24 h.

Fluvoxamine is a more potent inhibitor of lidocaine metabolism than ketoconazole and erythromycin in vitro

CYP3A4 is generally believed to be the major CYP enzyme involved in the biotransformation of lidocaine in man; however, recent in vivo studies suggest that this may not be the case. We have examined the effects of the CYP3A4 inhibitors erythromycin and ketoconazole and the CYP1A2 inhibitor fluvoxamine on the N-deethylation, i.e. formation of monoethylglycinexylidide (MEGX), and 3-hydroxylation of lidocaine by human liver microsomes. The experiments were carried out at lidocaine concentrations of 5 microM (clinically relevant concentration) and 800 microM. The formation of both MEGX and 3-hydroxylidocaine was best described by a two-enzyme model. At 5 microM of lidocaine, fluvoxamine was a potent inhibitor of the formation of MEGX (IC50 1.2 microM). Ketoconazole and erythromycin also showed an inhibitory effect on MEGX formation, but ketoconazole (IC50 8.5 microM) was a much more potent inhibitor than erythromycin (IC50 200 microM). At 800 microM of lidocaine, fluvoxamine (IC50 20.7 microM) and ketoconazole (IC50 20.4 microM) displayed a modest inhibitory effect on MEGX formation, whereas erythromycin was a weak inhibitor (IC50 >250 microM). The 3-hydroxylation of lidocaine was potently inhibited by fluvoxamine at both lidocaine concentrations (IC50 0.16 microM at 5 microM and 1.8 microM at 800 microM). Erythromycin and ketoconazole showed a clear inhibitory effect on the 3-hydroxylation of lidocaine at 5 microM of lidocaine (IC50 9.9 microM and 13.9 microM, respectively), but did not show a consistent effect at 800 microM of lidocaine (IC50 >250 microM and 75.0 microM, respectively). Although further studies are needed to elucidate the role of distinct CYP enzymes in the biotransformation of lidocaine in humans, the findings of this study suggest that while both CYP1A2 and CYP3A4 are involved in the metabolism of lidocaine by human liver microsomes, CYP1A2 is the more important isoform at clinically relevant lidocaine concentrations.

Repeated consumption of grapefruit juice considerably increases plasma concentrations of cisapride

BACKGROUND

Grapefruit juice increases the bioavailability of several drugs that are metabolized during first pass by CYP3A4. In this study, the effect of grapefruit juice on the pharmacokinetics of orally administered cisapride was investigated.

METHODS

In a randomized, two-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water three times a day for 2 days. On day 3, each subject ingested 10 mg cisapride with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 hour and 1 1/2 hours after cisapride administration. Timed blood samples were collected for 32 hours after cisapride intake, and a standard 12-lead ECG was recorded before the administration of cisapride and 2, 5, 8, and 12 hours later.

RESULTS

The mean peak plasma concentration of cisapride was increased by 81% (range, 38% to 138%; P < .01) and the total area under the plasma cisapride concentration-time curve by 144% (range, 65% to 244%; P < .01) by grapefruit juice. The time of the peak concentration of cisapride was prolonged from 1.5 to 2.5 hours (P < .05) and the elimination half-life from 6.8 to 8.4 hours (P < .05) by grapefruit juice. ECG tracings did not show any significant differences in the QTc interval between the grapefruit juice and control phases.

CONCLUSIONS

Grapefruit juice significantly increases plasma concentrations of cisapride, probably by inhibition of the CYP3A4-mediated first-pass metabolism of cisapride in the small intestine. Concomitant use of high amounts of grapefruit juice and cisapride should be avoided, at least in patients with risk factors for cardiac arrhythmia.

Midazolam alpha-hydroxylation by human liver microsomes in vitro: inhibition by calcium channel blockers, itraconazole and ketoconazole

The inhibitory effects of five calcium channel blockers (diltiazem, isradipine, mibefradil, nifedipine and verapamil) and three azole antifungal agents (itraconazole, hydroxyitraconazole and ketoconazole) on the alpha-hydroxylation of midazolam, a probe drug for CYP3A4-mediated interactions in humans, were studied in vitro using human liver microsomes. IC50 and Ki values were determined for each inhibitor. The kinetics of the formation of alpha-hydroxymidazolam were best described by simple Michaelis-Menten kinetics. The estimated values of Vmax and Km were 696 pmol min.-(1) mg(-1) and 7.46 micromol l(-1), respectively. All the compounds studied inhibited midazolam alpha-hydroxylation activity in a concentration-dependent manner, but there were marked differences in their relative inhibitory potency. Ketoconazole was the most potent inhibitor of midazolam alpha-hydroxylation (IC50 0.12 micromol l (-1)), being 10 times more potent than itraconazole (IC50 1.2 micromol l(-1)). The inhibitory effect of hydroxyitraconazole (IC50 2.3 micromol l (-1) was almost as large as that of itraconazole. Among the calcium channel blockers, mibefradil was the most potent inhibitor of the alpha-hydroxylation of midazolam, with an IC50 value (1.6 micromol l (-1)) similar to that of itraconazole. The other calcium channel blockers were much weaker inhibitors than mibefradil: verapamil exhibited a modest inhibitory effect with an IC50 of 23 micromol l(-1), while isradipine, nifedipine and diltiazem, with IC50 values ranging from 57 to >100 micromol l (-1), were weak inhibitors. This rank order of potency against the alpha-hydroxylation Qf midazolam was verified by the Ki values. With the exception of diltiazem, these in vitro results conform with the observed interaction potential of these agents with midazolam and many other CYP3A4 substrates in vivo in man.

Immunohistochemical detection of microsomal epoxide hydrolase in human synovial tissue

Microsomal epoxide hydrolase catalyses the hydrolysis of epoxides to water-soluble trans-dihydrodiols. We studied the expression of the hydrolase in synovial tissue samples from patients with osteoarthritis (n = 20), rheumatoid arthritis (n = 36), ankylosing spondylitis (n = 10) or psoriatic arthritis (n = 15) by use of immunohistochemistry with videodensitometric quantification of staining. Strong immunostaining for microsomal epoxide hydrolase was detected in tunica media of synovial blood vessels and moderate staining in synovial lining cells. Experiments with antibodies against CD68 and CLA suggested that both type A (macrophage-like) and type B lining cells (fibroblast-like synoviocytes) express the hydrolase. In addition, some of the subsynovial fibroblast-like cells, histiocytes and monocytes were intensively stained for microsomal epoxide hydrolase. In general, there were no major differences in the intensity of immunostaining for the hydrolase between the diagnostic groups. The enzyme may be involved in local hydrolysis of epoxide metabolites of endo- and xenobiotics in synovial tissue.

Mibefradil but not isradipine substantially elevates the plasma concentrations of the CYP3A4 substrate triazolam

BACKGROUND

The calcium channel blockers mibefradil and isradipine inhibit CYP3A4 in vitro. However, their in vivo inhibitory effects on CYP3A4 are not known in detail, although mibefradil was recently withdrawn from the market because of serious drug interactions.

METHODS

The effects of mibefradil and isradipine on the pharmacokinetics and pharmacodynamics of oral triazolam, a model substrate of CYP3A4, were studied in a randomized, double-blind crossover study with three phases. Nine healthy subjects took 50 mg mibefradil, 5 mg isradipine, or placebo orally once a day for 3 days. On day 3, each subject received a single 0.25 mg oral dose of triazolam. Thereafter, blood samples were collected up to 18 hours, and pharmacodynamic effects of triazolam were measured up to 8 hours.

RESULTS

Mibefradil increased the total area under the plasma triazolam concentration-time curve [AUC(0 - infinity)] 9-fold compared with placebo (P < .001). The peak plasma concentration of triazolam was increased 1.8-fold (3.4+/-0.1 ng/mL versus 1.8+/-0.2 ng/mL [mean +/- SEM]; P < .001), and the elimination half-life (t 1/2) was increased 4.9-fold (18.5+/-1.9 hours versus 4.0+/-0.5 hours; P < .001) by mibefradil. In addition, mibefradil was associated with increased pharmacodynamic effects of triazolam. In contrast to mibefradil, isradipine reduced the AUC(0 - infinity) and t 1/2 of triazolam by about 20% (P < .05) and had no significant effects on the pharmacodynamics of triazolam.

CONCLUSION

Mibefradil but not isradipine markedly increases the plasma concentrations of triazolam and thereby enhances and prolongs its pharmacodynamic effects, consistent with potent inhibition of CYP3A4.

Itraconazole decreases the clearance and enhances the effects of intravenously administered methylprednisolone in healthy volunteers

A possible interaction of itraconazole, a potent inhibitor of CYP3A4, with intravenously administered methylprednisolone, was examined. In this double-blind, randomized, two-phase cross-over study, 9 healthy volunteers received either 200 mg itraconazole or matched placebo orally once a day for 4 days. On day 4, a dose of 16 mg methylprednisolone as sodium succinate was administered intravenously. Plasma concentrations of methylprednisolone, cortisol, itraconazole, and hydroxyitraconazole were determined up to 24 hr. Itraconazole increased the total area under the plasma methylprednisolone concentration-time curve (AUC(0-infinity) 2.6-fold) (P<0.001), while the AUC (12-24) of methylprednisolone was increased 12.2-fold (P<0.001). The systemic clearance of methylprednisolone during the itraconazole phase was 40% of that during the placebo phase (P<0.01). The volume of distribution of methylprednisolone was not affected by itraconazole. The mean elimination half-life of methylprednisolone was increased from 2.1+/-0.3 hr to 4.8+/-0.8 hr (P<0.001) by itraconazole. The mean morning plasma cortisol concentration during the itraconazole phase, measured 24 hr after the administration of methylprednisolone, was only about 9% of that during the placebo phase (11.0+/-9.0 ng/ml versus 117+/-49.2 ng/ml; P<0.001). In conclusion, itraconazole decreases the clearance and increases the elimination half-life of intravenously administered methylprednisolone, resulting in greatly increased exposure to methylprednisolone during the night time and in enhanced adrenal suppression. Care should be taken when itraconazole or other potent inhibitors of CYP3A4 are used concomitantly with methylprednisolone.

Grapefruit juice substantially increases plasma concentrations of buspirone

BACKGROUND

Buspirone has a low oral bioavailability because of extensive first-pass metabolism. The effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of orally administered buspirone is not known.

METHODS

In a randomized, 2-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water 3 times a day for 2 days. On day 3, each subject ingested 10 mg buspirone with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 hour and 1 1/2 hours after buspirone administration. Timed blood samples were collected up to 12 hours after ingestion, and the effects of buspirone were measured with 6 psychomotor tests up to 8 hours after ingestion.

RESULTS

Grapefruit juice increased the mean peak plasma concentration of buspirone 4.3-fold (range, 2-fold to 15.6-fold; P < .01) and the mean area under the plasma buspirone concentration-time curve 9.2-fold (range, 3-fold to 20.4-fold; P < .01). The time of the peak concentration (tmax) of buspirone increased from 0.75 to 3 hours (P < .01), and the elimination half-life (t1/2) was slightly increased (P < .01) by grapefruit juice. A significant increase in the pharmacodynamic effects of buspirone by grapefruit juice was seen only in subjective overall drug effect (P < .01).

CONCLUSIONS

Grapefruit juice considerably increased plasma buspirone concentrations. The probable mechanism of this interaction is delayed gastric emptying and inhibition of the cytochrome P450 3A4-mediated first-pass metabolism of buspirone caused by grapefruit juice. Concomitant use of buspirone and at least large amounts of grapefruit juice should be avoided.

Immunohistochemical localization of metallothionein in synovial tissue of patients with chronic inflammatory and degenerative joint disease

Metallothioneins (MTs) are low-molecular-weight cytosolic proteins, which are thought to participate in metal homeostasis and protection against metal toxicity and oxidative stress. MT synthesis can be induced by a variety of inflammatory mediators and antirheumatic drugs, and high levels of MT have been implicated in resistance of cells to some antirheumatic drugs. We studied the expression and localization of MT in synovial tissue samples from patients with rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis or osteoarthritis (OA) by quantitative immunohistochemistry. Immunostaining for MT was detected in a large number of intimal lining cells in most of the investigated synovial tissue samples (75%). In a smaller proportion of samples (42%), some of the fibroblast-like cells of the subsynovial layer were also MT positive. Immunostaining and double-staining experiments with antibodies against monocyte-, macrophage- and leucocyte-associated antigens suggested that most of the MT-positive cells were intimal fibroblast-like cells and subsynovial fibroblasts. However, there were no statistically significant differences in the intensity of staining for MT between the rheumatic diseases and OA at the single-cell level. Thus, MT is expressed in synovial tissue and may participate in homeostatic and protective functions. The interindividual variability in the expression of MT in synovial tissue may be related to the therapeutic efficacy of the gold compounds and chemotherapeutic antirheumatic drugs sequestered by MT.

The area under the plasma concentration-time curve for oral midazolam is 400-fold larger during treatment with itraconazole than with rifampicin

OBJECTIVE

To determine the effects of treatment with itraconazole and rifampicin (rifampin) on the pharmacokinetics and pharmacodynamics of oral midazolam during and 4 days after the end of the treatment.

METHODS

Nine healthy volunteers received itraconazole (200 mg daily) for 4 days and, 2 weeks later, rifampicin (600 mg daily) for 5 days. In addition, they ingested 15 mg midazolam before the first treatment, 7.5 mg on the last day of itraconazole administration, and 4 days later, and 15 mg 1 day and 4 days after the last dose of rifampicin. The disposition of midazolam and its alpha-hydroxy metabolite was determined and its pharmacodynamic effects were measured.

RESULTS

During itraconazole treatment, or 4 days after, alpha-hydroxymetabolite the dose-corrected area under the plasma midazolam concentration time curve (AUC0-infinity) was 8- or 2.6-fold larger than that before itraconazole (i.e. 1707 or 695 versus 277 ng x h x ml(-1)), respectively. One day after rifampicin treatment, the AUC0-infinity of midazolam was 2.3% (i.e. 4.4 ng x h x ml(-1)) of the before-treatment value and only 0.26% of its value during itraconazole treatment; 4 days after rifampicin, the AUC0-infinity was still only 13% (i.e. 27.1 ng x h x ml(-1)) of the before-treatment value. The peak concentration and elimination half-life of midazolam were also increased by itraconazole and decreased by rifampicin. The ratio of plasma alpha-hydroxymidazolam to midazolam was greatly decreased by itraconazole and increased by rifampicin. In addition, the effects of midazolam were greater during itraconazole and smaller 1 day after rifampicin than without treatment.

CONCLUSION

Switching from inhibition to induction of cytochrome P450 3A (CYP3A) enzymes causes a very great (400-fold) change in the AUC of oral midazolam. During oral administration of CYP3A substrates that undergo extensive first-pass metabolism, similar changes in pharmacokinetics are expected to occur when potent inhibitors or inducers of CYP3A are added to the treatment. After cessation of treatment with itraconazole or rifampicin, the risk of significant interaction continues up to at least 4 days, probably even longer.

Expression of cyclooxygenase 1 and cyclooxygenase 2 in human synovial tissue: differential elevation of cyclooxygenase 2 in inflammatory joint diseases

OBJECTIVE

To compare the expression of the cyclooxygenase (COX) isoforms, COX-1 and COX-2, in synovial tissue samples between patients with inflammatory arthritis (i.e., rheumatoid arthritis [RA], ankylosing spondylitis [AS], or psoriatic arthritis [PsA]) and patients with osteoarthritis (OA).

METHODS

Paraffin-embedded sections of synovial tissue from patients with OA (n = 18), RA (n = 35), AS (n = 9), and PsA (n = 16) were immunostained for COX-1 and COX-2. Staining intensity was quantified videodensitometrically from specific synovial cell areas. In addition, samples of OA and RA synovial tissue were analyzed for levels of COX-1 and COX-2 messenger RNA (mRNA) using reverse transcriptase-polymerase chain reaction.

RESULTS

Strong COX-2 immunostaining was observed in synovial blood vessel endothelium, synovial lining cells, chondrocytes, and subsynovial fibroblast-like cells in patients with inflammatory arthritides. In the blood vessels, the mean (+/-SD) optical density (MOD) of staining was elevated, especially in AS samples (2.73 +/- 0.63), but also in PsA (1.99 +/- 0.66) and RA samples (1.54 +/- 0.73), in comparison with OA synovial tissue (0.84 +/- 0.30; P < 0.01 versus other groups). COX-1 staining was almost exclusively localized in synovial lining cells, with no significant differences in the MOD between the diseases. COX-2 mRNA expression was higher in RA than in OA samples (P < 0.05).

CONCLUSION

The expression of COX-2, but not the expression of COX-1, was found to be elevated in a disease-related pattern in the synovial tissue from patients with RA, AS, or PsA in comparison with OA samples, and was especially high in AS synovial tissue. These results may improve our understanding of the pathogenesis of different arthritic diseases, and may have implications for the use of selective COX-2 inhibitors in the treatment of inflammatory joint symptoms.

The role of beta-glucuronidase in drug disposition and drug targeting in humans

Glucuronides of drugs often accumulate during long term therapy. The hydrolysis of glucuronides can be catalysed by beta-glucuronidase, an enzyme expressed in many tissues and body fluids in humans. The possible contribution of beta-glucuronidase to drug disposition in humans has not been assessed in a systematic manner, but this enzyme may be able to release, locally or systemically, the active or inactive parent compound from drug glucuronides, thereby modifying the disposition and action of these drugs. Based on the information available on the localisation, expression and variability of beta-glucuronidase, the concept of beta-glucuronidase-mediated drug metabolism is outlined in this article using examples from the literature. Since some issues surrounding the beta-glucuronidase-mediated deconjugation of drug glucuronides still need to be clarified in humans, additional data from animal models supporting this concept have been included. Moreover, as beta-glucuronidase has already been proven to be useful in tumour specific bioactivation of glucuronide prodrugs of anticancer agents, we also focus on anticancer prodrug approaches utilising beta-glucuronidase. This review summarises the role of beta-glucuronidase in drug disposition and drug targeting in humans.