A new simple diagnostic assay for the identification of the major CYP2D6 genotypes by DNA sequencing analysis

AIM

To establish a method suitable for diagnostic genotyping of CYP2D6 alleles by DNA sequencing.

METHODS

Initial PCR reactions were performed to specifically amplify exons 3, 4, 5 and 6 of the CYP2D6 gene using primers previously published. New primers were used to identify *2, *3, *4, *6, *7, *8, *9 and *41 in 2 sequencing reactions. Additional primers were designed for reverse sequencing in samples with 1 or 3 b.p. deletions. Previously published assays were used to detect *5, *10 and *16 alleles to complete genotype assignment.

RESULTS

We reliably detected the nonfunctional alleles, *3, *4, *6, *7 and *8, which are associated with the poor metabolizer phenotype, and 2 important alleles associated with decreased enzyme activity, *9 and *41. Observed allele frequencies were comparable to those found previously in Caucasian populations.

CONCLUSION

CYP2D6 genotype has been shown in previous clinical studies to be a good predictor of CYP2D6 phenotype and, therefore, related to therapeutic response and the risk of drug toxicity. This genotyping method is simple and reliable, and, therefore, can be routinely performed on an isolated patient sample, providing a relatively quick turnaround time needed for clinical practice. In addition, the simultaneous drawing of blood with the commencement of drug therapy will allow dosage adjustment on the basis of the CYP2D6 genotype to reduce the risk of adverse drug reactions.

Determination of perhexiline and hydroxyperhexiline in plasma by liquid chromatography–mass spectrometry

A method for the quantitative determination of perhexiline and its main hydroxylated metabolites in human plasma, based on liquid chromatography-mass spectrometry (LC-MS), was developed. The method used protein precipitation with acetonitrile followed by dilution with water and subsequent direct injection of the extract into the LC-MS system. Hexadiline was used as internal standard and the intra-assay coefficients of variation were <or=5% for perhexiline and cis-hydroxyperhexiline over the target concentration range in patients. The lower limits of quantification were 0.005mg/l for perhexiline and 0.015mg/l for cis-hydroxyperhexiline, and the measuring ranges were from 0.05 to 3.0 and from 0.2 to 6.0mg/l, respectively. The method was compared with an established HPLC method with fluorescence detection and the correlation between the methods was close to 1 for both compounds. The predominant form of hydroxyperhexiline in 87% of the patient samples was found to be one of the diastereomeric pairs of cis-hydroxyperhexiline. In patients not forming this metabolite, trans-hydroxyperhexiline could be detected. We conclude that the present LC-MS method is suitable for use in a clinical routine laboratory.

Optimisation of the comet genotoxicity assay in freshly isolated murine hepatocytes: detection of strong in vitro DNA damaging properties for styrene

While the comet assay is used to detect DNA damage in isolated cells following exposure to chemicals in vitro, few publications report the use of the procedure in liver cells isolated from mice. Our initial efforts to use the assay to assess DNA damage in mouse hepatocytes maintained on collagen-coated dishes were hampered by high levels of baseline damage in controls, which appeared to result from mechanical damage sustained during the dislodgement of adherent cells in the early stages of the assay protocol. Here we describe an efficient version of the comet assay in cultured mouse hepatocytes that involves careful recovery of cells using a "scraping" buffer supplemented with 10% high purity grade DMSO. Use of this buffer strongly diminished the frequency of false positives. Using the industrial reagent styrene as a positive control in the optimised procedure, non-cytotoxic concentrations of this substance (2.5-10 mM) significantly increased mean comet tail length, area, and moment. Co-incubation with the CYP inhibitor SKF-525A strongly attenuated these effects of styrene. Collectively, these findings confirm this method is highly suitable for the detection of DNA damage by bioactivation-dependent compounds in freshly isolated mouse hepatocytes.

In vivo perturbation of rat hepatocyte canalicular membrane function by diclofenac

Clinical use of diclofenac is associated with a small but significant incidence of hepatotoxicity. It has been reported that in vivo diclofenac treatment results in decreased activity of the extracellular canalicular membrane protein dipeptidylpeptidase IV in rats as a consequence of protein adduct formation by its electrophilic metabolite diclofenac acyl glucuronide. The present study has investigated the effects of in vivo diclofenac treatment (15 mg/kg/day for 7 days) on the activity of an another four rat extracellular canalicular membrane proteins. Animals administered diclofenac (n = 6) had 47.9, 60.4, and 51.6% lower (p < 0.05) canalicular activities of gamma-glutamyltransferase, Mg(2+)-ATPase, and leucine aminopeptidase, respectively, compared with controls (n = 6), but there was no difference in alkaline phosphatase activity. In general, protein adduct formation by acyl glucuronides has been associated with decreased protein function, and the lower canalicular enzyme activities in diclofenac-treated rats may suggest that gamma-glutamyltransferase, Mg(2+)-ATPase, and leucine aminopeptidase are also targets of adduct formation by acyl glucuronide metabolites of diclofenac. However, intracellular redistribution and/or decreased synthesis of these enzymes would also be consistent with our results. The ability of diclofenac acyl glucuronide (200 microg/ml) to form covalently bound adducts with gamma-glutamyltransferase (10 mg/ml) was demonstrated following in vitro incubations (16 h, pH 7.4, and 37 degrees C) in which 20.7 +/- 2.1 ng of diclofenac were covalently bound per milligram of protein. In these in vitro studies, the low concentration of protein adducts formed was not associated with any significant change in gamma-glutamyltransferase activity.

Hepatic disposition of the acyl glucuronide 1-O-gemfibrozil-beta-D-glucuronide: effects of clofibric acid, acetaminophen, and acetaminophen glucuronide

Glucuronidation of carboxylic acid compounds results in the formation of electrophilic acyl glucuronides. Because of their polarity, carrier-mediated hepatic transport systems play an important role in determining both intra- and extrahepatic exposure to these reactive conjugates. We have previously shown that the hepatic membrane transport of 1-O-gemfibrozil-beta-D-glucuronide (GG) is carrier-mediated and inhibited by the organic anion dibromosulfophthalein. In this study, we examined the influence of 200 microM acetaminophen, acetaminophen glucuronide, and clofibric acid on the disposition of GG (3 microM) in the recirculating isolated perfused rat liver preparation. GG was taken up by the liver, excreted into bile, and hydrolyzed within the liver to gemfibrozil, which appeared in perfusate but not in bile. Mean +/- S. D. hepatic clearance, apparent intrinsic clearance, hepatic extraction ratio, and biliary excretion half-life of GG were 10.4 +/- 1.4 ml/min, 94.1 +/- 17.9 ml/min, 0.346 +/- 0.046, and 30.9 +/- 4.9 min, respectively, and approximately 73% of GG was excreted into bile. At the termination of the experiment (t = 90 min), the ratio of GG concentrations in perfusate, liver, and bile was 1:35:3136. Acetaminophen and acetaminophen glucuronide had no effect on the hepatic disposition of GG, suggesting relatively low affinities of acetaminophen conjugates for hepatic transport systems or the involvement of multiple transport systems for glucuronide conjugates. In contrast, clofibric acid increased the hepatic clearance, extraction ratio, and apparent intrinsic clearance of GG (P <.05) while decreasing its biliary excretion half-life (P <.05), suggesting an interaction between GG and hepatically generated clofibric acid glucuronide at the level of hepatic transport. However, the transporter protein(s) involved remains to be identified.

Hepatic disposition of electrophilic acyl glucuronide conjugates

Acyl glucuronides are a unique class of electrophilic metabolites, capable of non-enzymatic reactions including acylation and/or glycation of endogenous macromolecules, hydrolysis to reform the parent aglycone, and intra-molecular rearrangement. Three human UDP-glucuronosyltransferases (UGTs) catalyzing the hepatic glucuronidation of carboxylic acid drugs have been identified, UGT1A3, UGT1A9 and a UGT2B7 variant. Within the liver, acyl glucuronides also undergo enzymatic hydrolysis by beta-glucuronidase and esterases which, like the UGTs, are located in the endoplasmic reticulum. In addition, the liver also transports acyl glucuronides between the sinusoidal circulation and bile. Due to their polarity, membrane transport of acyl glucuronides is carrier-mediated, resulting in the establishment of significant concentration gradients between sinusoidal circulation, hepatocyte and bile, in the order of 1:50:5,000 in these compartments, respectively. As a result of exposure to high acyl glucuronide concentrations, the liver is a major target of protein adduct formation. Dipeptidylpeptidase IV, UGTs and tubulin have been identified as intra-hepatic targets of adduct formation by acyl glucuronides. Adduct formation results in altered protein activity and potentially contributes to hepatotoxicity. Hepatic protein adducts are also immunogenic and may cause immune mediated cytotoxicity. Both intra- and extra-hepatic exposure to acyl glucuronides depends not only on the efficiency of glucuronidation and hydrolysis by the liver, but also on the efficiency of the hepatic membrane transport systems. Thus, changes in membrane transporter activities, as may occur due to saturation or drug-drug interactions, can significantly affect acyl glucuronide disposition, adduct formation and the disposition of parent aglycone, thereby affecting clinical efficacy and toxicity of acyl glucuronide forming drugs.

In vitro covalent binding of nafenopin-CoA to human liver proteins

Endogenous fatty acyl-CoAs play an important role in the acylation of proteins. A number of xenobiotic carboxylic acids are able to mimic fatty acids, forming CoA conjugates and acting as substrates in pathways of lipid metabolism. In this study nafenopin, a substrate for human hepatic fatty acid-CoA ligases, was chosen as a model compound to study xenobiotic acylation of human liver proteins. (3)H-nafenopin (+/- unlabeled palmitate) or (14)C-palmitate (+/- unlabeled nafenopin) were incubated for up to 120 min at 37 degrees C with ATP, CoA, and homogenate protein (1 mg/ml) from four individual human livers. Nafenopin covalently bound to proteins was detectable in all human livers and increased with time. Nafenopin adduct formation was directly proportional to nafenopin-CoA formation (r = 0.985, p < 0.05). Attachment of nafenopin to proteins involved both thioester and amide linkages with 76 and 24% of adducts formed with proteins > 100 and 50-100 kDa, respectively. Protein acylation by palmitate was also demonstrated. Palmitate significantly inhibited nafenopin-CoA formation by 29% but had no effect on nafenopin-CoA-mediated protein acylation. In contrast, nafenopin significantly inhibited protein palmitoylation by palmitoyl-CoA. This is the first study to demonstrate a direct relationship between xenobiotic-CoA formation, acylation of human liver proteins, and inhibition of endogenous palmitoylation. The ability of xenobiotics to acylate tissue proteins may have important biological consequences including perturbation of endogenous regulation of protein localization and function.

Some international approaches to aminoglycoside monitoring in the extended dosing interval era

Aminoglycosides have rightly remained a cost-effective anti-microbial strategy for the treatment of gram-positive infections for some 25 years. However, in recent years there has been a review of the traditional thrice-daily administration regimen in favor of an extended dosing interval strategy that takes into account the individual patient's renal function. The general recommendations that have been provided to date have been adopted in various ways internationally. These approaches were a matter of discussion for the Clinical Pharmacokinetics Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology at its congress (Vancouver, Canada; November 1997), and will again be a workshop issue at the Cairns (Australia) congress of the Association (September 1999). The present report provides examples of how these practices have been applied at a group of centers from Canada (2 centers), The Netherlands, Egypt, and Australia. These reports demonstrate a variety of approaches and highlight the need for further research for assessing clinical outcomes from different dosing strategies.

Assessment of interlaboratory performance in the provision of perhexiline therapeutic drug monitoring services in Australia

Perhexiline is a prophylactic antianginal agent particularly useful in patients whose angina is poorly controlled or refractory to conventional drug regimens. Although perhexiline can cause serious hepatic and neurological toxicity, maintaining trough plasma concentrations between 0.15-0.60 mg/L minimizes the risk of toxicity while providing relief of angina symptoms in a majority of patients. All pathology laboratories are required to participate in interlaboratory proficiency testing (PT) programs. The authors therefore initiated a monthly PT program to assess the performance of Australian laboratories measuring perhexiline (n = 8). PT specimens included perhexiline-spiked drug-free human plasma and pooled plasma from patients administered perhexiline. The performance of 8 Australian laboratories participating in the program was examined over a 30-month period. The mean relative standard deviation of the group was 18.2%. All centers performed well with respect to accuracy, achieving mean percentage bias within +/-8% of target perhexiline concentrations. The usefulness of the PT program was highlighted by the identification of two laboratories with an unacceptable degree of variability (up to 30% of results varied more than +/-55% from the target concentration), and the identification of potential analytical problems with the use of perhexiline metabolite concentrations for determining patients' hydroxylator status. Continued and improved use of PT by pathology laboratories is essential to ensuring the safe and effective clinical use of perhexiline.

Hepatic disposition of the acyl glucuronide1-O-gemfibrozil-beta-D-glucuronide: effects of dibromosulfophthalein on membrane transport and aglycone formation

The liver plays an important role in the disposition of acyl glucuronides by determining their extent of formation, biliary excretion, and efflux into blood. Thus, both intrahepatic and extrahepatic exposure to these reactive polar conjugates depends on the efficiency of hepatic transport mechanisms, which may be shared with other nonbile acid organic anions. Using the isolated perfused rat liver preparation, the hepatic disposition of the acyl glucuronide, 1-O-gemfibrozil-beta-D-glucuronide, was examined in the presence of the organic anion dibromosulfophthalein (DBSP). Using a recirculating system, livers were perfused for 90 min with an erythrocyte-free perfusion medium containing 1% (w/v) albumin and 1-O-gemfibrozil-beta-D-glucuronide (3 microM) alone (n = 6) or with DBSP (200 microM, n = 7). The glucuronide was avidly taken up by the liver, excreted into bile, and hydrolyzed within the liver to its aglycone, gemfibrozil. DBSP significantly (P <.05) lowered the conjugate's mean hepatic clearance (8.98-5.17 ml/min), intrinsic clearance (44.0-17.7 ml/min), and fraction eliminated in bile (72. 8-48.7% of the dose), while increasing perfusate gemfibrozil concentrations (0.52-0.92 microM at 90 min). Furthermore, DBSP significantly (P <.05) lowered the ratio of intrahepatic to unbound perfusate concentrations of 1-O-gemfibrozil-beta-D-glucuronide (139. 0-35.0) and showed a trend to lower the ratio of bile to intrahepatic concentrations (111.3-76.2, P =.05). Thus, the study demonstrated that DBSP inhibited both the sinusoidal uptake and canalicular transport of 1-O-gemfibrozil-beta-D-glucuronide, suggesting that the hepatic membrane transport of acyl glucuronides is carrier mediated and shared with other organic anions.

Lamotrigine and therapeutic drug monitoring: retrospective survey following the introduction of a routine service

AIMS

To review (retrospectively) the relationships between lamotrigine (LTG) dosage and plasma concentrations based on data generated in a routine therapeutic drug monitoring laboratory from a heterogeneous sample of patients with epilepsy. To distinguish patients taking concomitant anti-epileptic therapy which induced or inhibited drug metabolising enzymes, or a combination of both, together with LTG. To survey medical staff who use a routine LTG assay service with a view to establishing the utility of higher plasma LTG concentrations than those used in early clinical trials.

METHODS

All patient assays for LTG received over a 12 month period (339 requests from 149 patients) were reviewed and relationships between dosage and concentration calculated and grouped according to concomitant antiepileptic drug therapy. The doctors requesting the tests were surveyed by questionnaire (n=40 of 67 responded). They were asked for details about the patient's seizure control, rationale used for LTG dosage adjustment and their acceptance of the proposed 'therapeutic range' adopted by the laboratory of 3-14 mg(-1).

RESULTS

Linear relationships were demonstrated between LTG dosage and concentration for the 3 treatment groups (LTG plus valproic acid (VPA), LTG plus enzyme inducing antiepileptic drugs, and LTG plus VPA and inducers), however, there were significant differences between groups (P<0.001) with a 4.4 fold difference in dosage: concentration ratios between the LTG plus VPA group and the LTG plus inducers group. The questionnaire showed that the therapeutic range was well accepted by 88% of responders, none of whom considered this higher range to be wrong.

CONCLUSIONS

Metabolic inhibition by VPA was shown to have a marked effect on LTG kinetics, suggesting either a significant LTG dosage reduction is required if plasma LTG concentrations are elevated, or alternatively, higher plasma LTG concentrations could be attained from lower dosages. The higher therapeutic range adopted by the laboratory (3-14 mg(-1)) was widely accepted and increasingly applied in clinical practice in the management of patients with epilepsy.

Short-term myocardial uptake of d- and l-sotalol in humans: relation to hemodynamic and electrophysiologic effects

The myocardial concentration of many cardioactive drugs has been identified as an important determinant of their short-term effects in previous studies. Although sotalol is frequently administered via short-term intravenous injection, no previous studies had sought to correlate its uptake by the heart with its various effects. We determined the time course of short-term uptake of d,l-sotalol by human myocardium in vivo and investigated the relation between myocardial content of sotalol and the short-term hemodynamic, electrocardiographic, and electrophysiologic effects of the drug. Sixteen patients received a 20-mg intravenous bolus of sotalol at the time of diagnostic cardiac catheterization. Myocardial content of d- and l-sotalol (by using a paired transcoronary sampling technique) and the short-term hemodynamic and electrophysiologic effects of the drug were determined < or = 20 min after injection. Myocardial accumulation of sotalol was not enantioselective, proceeded very rapidly (maximal at 0.74 +/- 0.10 min, representing 2.05 +/- 0.45% of the total injected dose), and was not significantly influenced by left ventricular systolic function or the extent of coronary artery disease. Approximately one third of peak myocardial content was still present 17.5 min after sotalol administration. Maximal effects of the drug (reduction in spontaneous heart rate, p < 0.005; reduction in maximal rate of LV pressure increase (LV+dP/dtmax, p < 0.005); and prolongation of PR intervals, p < 0.02) were delayed by approximately 10 min relative to maximal myocardial sotalol content. The significant prolongation of AH intervals (p < 0.01) and atrioventricular nodal effective refractory periods (p < 0.0002) that was observed was also maximal 10 min after administration of sotalol. Thus a consistent delay between myocardial sotalol content and the short-term effects of the drug was observed. In conclusion, the accumulation of both d- and l-sotalol by the human myocardium is more rapid than that of any other agent studied to date, with considerable hysteresis between myocardial drug uptake and subsequent cardiac effects.

High-performance liquid chromatography quantitation of plasma lamotrigine concentrations: application measuring trough concentrations in patients with epilepsy

Lamotrigine is a phenyltriazine anticonvulsant recently approved for clinical use. A high-performance liquid chromatographic (HPLC) method was developed using a silica column (5 microm) with an aqueous methanol mobile phase consisting of 94% methanol, 5.92% water, and 0.08% NH4H2PO4 adjusted to a final apparent pH of 4.0 and pumped at a flow rate of 1.0 ml/minute. Ultraviolet detection was carried out at a wavelength of 280 nm, and plasma samples were prepared for HPLC analysis by extraction into ethyl acetate after basification. Retention times for lamotrigine and its internal standard (BWA725C) were 10.3 and 11.2 minutes, respectively, and there was no chromatographic interference from other commonly coadministered anticonvulsants. Calibration curves were linear over a concentration range of 0.5 to 30 mg/l, with intra-assay and interassay coefficients of variation less than 8%. Assessment of assay performance in an international quality assurance program showed an average bias of 0.3% compared with the consensus mean. A review of 52 patient specimens showed that, if patients were grouped according to coadministered anticonvulsants, a significant correlation between lamotrigine dosage and concentration was evident in those coadministered valproate (in the absence of metabolic inducers) and in those coadministered a combination of valproate and inducers, but not in patients coadministered inducers alone. Mean (SD) trough concentrations were 9.2 (5.2), 2.8 (1.3), and 3.8 (2.8) mg/l in the valproate, inducer, and combination groups, respectively.

Genotoxicity of acyl glucuronide metabolites formed from clofibric acid and gemfibrozil: a novel role for phase-II-mediated bioactivation in the hepatocarcinogenicity of the parent aglycones?

Glucuronides formed from carboxylate-containing xenobiotics are more chemically reactive than most Phase II conjugates. However, while they have been shown to form protein adducts, their reactions with DNA have received little attention. We thus used the M13 forward mutational assay to assess the genotoxicity of acyl glucuronides formed from two widely used fibrate hypolipidemics, clofibric acid and gemfibrozil. Single-stranded M13mp19 bacteriophage DNA was incubated in pH 7.4 buffer for 16 h in the presence of 0, 1, 2.5, and 5 mM concentrations of each glucuronide as well as the respective aglycones. The modified DNA was then transfected into SOS-induced competent Escherichia coli JM105 cells and the transfection efficiency was determined after phage growth overnight at 37 degrees C. Significantly, both acyl glucuronides, but not the aglycones, caused a concentration-dependent decrease in the transfection efficiency of the DNA, with a greater than 80% decrease in phage survival produced by the 5 mM concentrations of the glucuronides. No increase in lacZa mutations accompanied the loss of phage survival. We propose that these genotoxic effects involve reactions with nucleophilic centers in DNA via a Schiff base mechanism that is analogous to the glycosylation of DNA by endogenous sugars. Since strand nicking is known to accompany such damage, we also analyzed glucuronide-treated pSP189 plasmids for strand breakages via agarose gel electrophoresis. Both clofibric acid and gemfibrozil glucuronides produced significant concentration-related strand nicking and exhibited over 10-fold greater reactivity than the endogenous glycosylating agent, glucose 6-phosphate. On the basis of these findings, the possibility that this novel bioactivation route participates in the carcinogenicity of the fibrate hypolipidemics deserves investigation.

Effects of gemfibrozil and clofibric acid on the uptake of taurocholate by isolated rat hepatocytes

Clinical use of fibrate hypolipidaemic agents has been associated with an increased incidence of hepatobiliary dysfunction including increased bile lithogenicity, gallstone formation, and cholestasis. The hepatic transport of bile acids plays an important role in bile formation and flow, and interference with the hepatocellular transport of bile acids may result in hepatobiliary dysfunction. The aim of this study was to investigate the effects of gemfibrozil and clofibric acid on the uptake of taurocholate by rat isolated hepatocytes. In control hepatocyte preparations (N = 5) at 37 degrees, the uptake of taurocholate was described by saturable Michaelis-Menten kinetics with a mean (+/-SD) Km of 44.1 +/- 10.2 microM and Vmax of 62.0 +/- 23.0 nmol/10(6) cells/min. In the presence of 200 microM clofibric acid, there was no significant change in the kinetics of taurocholate uptake. However, in the presence of 200 microM gemfibrozil there was a statistically significant (P < 0.05) decrease in the Vmax of taurocholate uptake (32.0 +/- 18.2 nmol/10(6) cells/min, N = 5) and no change (P > 0.05) in Km (48.5 +/- 29.5 microM, N = 5). Gemfibrozil behaved as a non-competitive inhibitor of taurocholate uptake, with a Ki of 144 microM, which is approximately 50 times higher than the unbound gemfibrozil concentrations achieved clinically in humans. Thus, gemfibrozil and clofibric acid did not appear to directly alter the hepatic uptake of taurocholate at clinically relevant concentrations.

Reducing the cost of cyclosporin assays: modification of the EMIT 2000 method

Cyclosporin is the leading immunosuppressant agent in organ transplantation, and therapeutic drug monitoring forms an integral part of patient management in most institutions. In the authors' laboratory, the cost of cyclosporin assays represents a major fraction of total consumable expenditure. At present, an average of 4,300 patient cyclosporin assays are performed annually using the EMIT 2000 method (Behring-Syva) on the Cobas Mira analyser (Roche), at a cost of AUD$50,000 in kits alone. As a means of reducing laboratory costs, the manufacturer's recommended method was modified by decreasing all of the reagent and sample volumes in the "Analytical" section of the Cobas Mira cyclosporin programme by 33%. Assay performance was monitored over a 10-month period and compared to that of the unmodified method. Calibration curves were stable, requiring a one-point correction on average of once every 12 days, and a full calibration once ever 1.7 months. Interassay variability was not different to that previously reported for the unchanged method, with mean (SD, CV) concentrations for trilevel quality control specimens of 86.5 micrograms/L (10.2, 11.9%), 185.9 micrograms/L (11.4, 6.2%) and 408.5 micrograms/l (28.9, 7.1%). From 24 specimens assayed in an international quality assurance programme, the results of 23 were within 1.2 SD of the group mean for the EMIT method, with an average bias of 0.8%. With the current modifications, we were able to perform an average of 105 patient assays per kit compared to the previous 71, equating to an annual saving the AUD$16,600.

Interaction of human serum albumin with the electrophilic metabolite 1-O-gemfibrozil-beta-D-glucuronide

Acyl glucuronides are electrophilic metabolites that are readily hydrolyzed, undergo intramolecular rearrangement, and bind covalently to endogenous proteins. Gemfibrozil is a fibrate lipid-lowering agent that is extensively metabolized to an acyl glucuronide conjugate in humans. The aims of this study were to examine the interactions of 1-O-gemfibrozil-beta-D-glucuronide with human serum albumin. The degradation of 1-O-gemfibrozil-beta-D-glucuronide (approximately 200 microM) was examined in vitro during incubations at 37 degrees C with phosphate buffer (pH 7.4 or 9.0), solutions of human serum albumin (pH 7.4), or fresh human plasma (pH 7.4). The effects of diazepam, oxyphenbutazone, and gemfibrozil on the degradation of 1-O-gemfibrozil-beta-D-glucuronide, and its reversible binding to albumin were also studied. A pilot in vivo study was performed on two patient volunteers administered 1 g/day p.o. gemfibrozil. 1-O-Gemfibrozil-beta-D-glucuronide was unstable, with degradation half-lives in buffer of 4.1 hr and 44 hr at pH 9.0 and 7.4, respectively; and 8.5 hr and 5.5 hr in pH 7.4 solutions of human serum albumin or fresh plasma, respectively. Degradation was dependent on pH and the presence of albumin, which seemed to accelerate the intramolecular rearrangement and hydrolysis of the conjugate. 1-O-Gemfibrozil-beta-D-glucuronide was highly reversibly bound to albumin, with a mean unbound fraction of 0.028, and its degradation seemed to be related to the degree of reversible binding. Hydrolysis and covalent binding were associated with the site II binding domain on albumin, because only diazepam inhibited these reactions. However, intramolecular rearrangement was increased when binding to the site I domain was inhibited. Covalent binding was also detected in vivo to human plasma proteins. The half-life of the gemfibrozil-protein adducts was 2.5-3 days. Albumin plays an important role in the disposition of acyl glucuronides by acting as: i) a transporter protein; ii) a potential catalyst for their degradation and, therefore, clearance; and iii) a target for covalent adduct formation.

Disposition of gemfibrozil and gemfibrozil acyl glucuronide in the rat isolated perfused liver

Acyl glucuronides are reactive electrophilic metabolites and in vivo are readily hydrolyzed, undergo intramolecular rearrangement, and bind covalently to proteins. The isolated perfused liver preparation, using male Sprague-Dawley rats, was used to examine the hepatic disposition of the fibrate hypolipidemic agent gemfibrozil and its acyl glucuronide metabolite, 1-O-gemfibrozil-beta-D-glucuronide. Using a recirculating design, erythrocyte-free perfusion medium containing 1% (w/v) albumin was delivered to the liver via the portal vein at a flow rate of 30 ml/min, and for each experiment was spiked with either gemfibrozil (N = 4) or 1-O-gemfibrozil-beta-D-glucuronide (N = 4) at initial concentrations of 120 microM and 21 microM, respectively. In the gemfibrozil perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio of gemfibrozil, and the fraction of eliminated gemfibrozil excreted in bile as the glucuronide conjugate were 2.73 (0.30) ml/min, 76.9 (5.6) min, 0.091 (0.012), and 0.347 (0.154), respectively. In the 1-O-gemfibrozil-beta-D-glucuronide perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio, and fraction excreted in bile as the glucuronide conjugate were 19.5 (2.1) ml/min, 8.7 (0.9) min, 0.649 (0.068), and 0.534 (0.077), respectively. The higher hepatic extraction ratio for 1-O-gemfibrozil-beta-D-glucuronide could mostly be attributed to its higher unbound fraction in perfusate (0.182), compared with that of the parent drug (0.004), because the conjugate had a lower intrinsic clearance (305 ml/min) compared with the aglycone (751 ml/min). Control perfusions, conducted in the absence of a liver, showed negligible degradation of 1-O-gemfibrozil-beta-D-glucuronide over 90 min. However, in the presence of a liver, approximately 25% of 1-O-gemfibrozil-beta-D-glucuronide added to perfusate was hydrolyzed to gemfibrozil over 90 min. The study demonstrates the importance of the liver in the formation, uptake, hydrolysis, and excretion of 1-O-gemfibrozil-beta-D-glucuronide.

Reactivity of gemfibrozil 1-o-beta-acyl glucuronide. Pharmacokinetics of covalently bound gemfibrozil-protein adducts in rats

Acyl glucuronides are electrophilic metabolites that are readily hydrolyzed, undergo intramolecular rearrangement, and mediate the covalent binding of many acidic drugs to endogenous proteins. Gemfibrozil is extensively metabolized to gemfibrozil acyl glucuronide in humans and rats. The aims of this study were to demonstrate the reactivity of gemfibrozil glucuronide, determine whether gemfibrozil formed covalently bound protein adducts in vivo, describe the pharmacokinetics of adduct formation, and examine the role of gemfibrozil glucuronide in adduct formation. Rats were administered 150 mg/kg gemfibrozil daily for up to 37 days and killed 1, 2, 5, 10, 19, and 37 days after commencement of dosing, and 1, 2, 3, 8, 17, and 30 days after cessation of dosing. Plasma, liver, kidney, and heart were examined for adduct formation. Plasma was quantitatively the most important site for formation of gemfibrozil-protein adducts with mean (SE) steady-state concentrations of 31.40 (2.40) ng/mg protein attained by approximately the 10th day of dosing. Adduct half-life in plasma was 3.1 days, consistent with the elimination half-life of albumin. Mean (SE) kidney, liver, and heart steady-state adduct concentrations were 2.13 (0.11), 0.89 (0.35), and 0.95 (0.07) ng/mg protein, respectively. The rate of gemfibrozil-protein adduct accumulation seemed greatest in liver, but was similar in kidney and plasma, with approximately 2x, 16x, and 30x accumulation, respectively, over the dosing interval. In all tissues, adduct half-lives were significantly greater than those of the noncovalently bound gemfibrozil or gemfibrozil glucuronide.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis, characterisation and direct high-performance liquid chromatographic analysis of gemfibrozil 1-O-beta-acylglucuronide

Gemfibrozil 1-O-beta-acylglucuronide was purified from the urine of a volunteer administered gemfibrozil, and an isocratic reversed-phase HPLC method was developed for its direct measurement. Quantitation of gemfibrozil and gemfibrozil 1-O-beta-acylglucuronide was carried out from plasma, following extraction from acidified specimens into ethyl acetate, on a 5-microns CN reversed-phase column with a mobile phase (pH 3.5) containing acetonitrile, tetrabutylammonium sulphate and distilled water, using fluorescence detection at 284 nm excitation and 316 nm emission. Calibration curves were linear for both compounds over a concentration range of 0.1 to 40 mg/l, with intra-assay coefficients of variation < 5% at concentrations of 20.0, 2.0 and 0.2 mg/l, and inter-assay coefficients of variation < 10%. No degradation of gemfibrozil 1-O-beta-acylglucuronide was detected as a result of the analytical procedure. However, a preliminary application of the method indicates that gemfibrozil acylglucuronide is chemically unstable undergoing intra-molecular rearrangement and hydrolysis under physiological conditions.

High-performance liquid chromatography determination of clonazepam in plasma using solid-phase extraction

The use of high-performance liquid chromatography for therapeutic drug monitoring of clonazepam has previously been limited by low sensitivity and labor-intensive liquid-liquid extractions. The present method was developed employing a rapid solid-phase extraction, thus minimising sample workup and providing analytical sensitivity down to 2 micrograms/L using 1 ml of plasma. Plasma samples were loaded onto C18 solid-phase extraction columns, and clonazepam and its internal standard (methyl-clonazepam) were eluted with methanol, dried, and reconstituted in 130 microliters of mobile phase. Chromatographic separation was achieved using a 3-microns RP18 column at 40 degrees C and a mobile phase of 32% acetonitrile and 0.5% glacial acetic acid in distilled water at 0.5 ml/min. Detection was carried out using ultraviolet absorbance at 306 nm. Retention times for clonazepam and methyl-clonazepam were approximately 7 and 12 min respectively. Standard curves were linear over a range of 5-200 micrograms/L with intraassay coefficients of variation of 1.2 and 4.8% at 200 and 5 micrograms/L, respectively. Plasma concentrations measured in patient samples were not statistically different from those obtained using an established gas chromatographic method, and quality control specimens from the Heathcontrol EQA Scheme were consistently within +/- 1.2 SD of the group means. There was no chromatographic interference from other benzodiazepines or other drugs used for the treatment of epilepsy.

Experiences with the enzyme-multiplied immunoassay cyclosporine specific assay in a therapeutic drug monitoring laboratory

Cyclosporin-A (CsA) monitoring is well established in the management of most organ transplant patients. The present communication reviews the performance of the recently introduced specific enzyme-multiplied immunoassay (EMIT) CsA method during the first 7 months of its operation and compares costs of providing this service with those of the specific 125I radioimmunoassay (RIA) method previously employed in this clinical laboratory. Results suggest that the EMIT method performed well, giving long calibration curve stability (up to 12 weeks), and only 4.4% of the 31 kits through this period were consumed in assaying calibration standards compared with 20.8% with RIA. However, more quality control assays were performed, with the net result that only a slight improvement in the percentage of kit consumed in patient assays was noted (74.0% compared with 70.3%) with the EMIT method. This method appears to have been well accepted clinically as the CsA assay request rate over this period increased by 23% and, since it is both specific and rapid, is, therefore, recommended as the best CsA method currently available.

Specific enzyme-multiplied immunoassay and fluorescence polarization immunoassay for cyclosporin compared with Cyclotrac [125I]radioimmunoassay

The analysis of cyclosporin-A (CsA) has proved a valuable adjunct to clinical care of patients who have received organ grafts. The measurement of CsA in whole blood by specific methods has recently taken a new direction with the introduction of a range of rapid methods, including a homogeneous enzyme immunoassay technique (EMIT) and a monoclonal fluorescence polarization immunoassay (FPIA). The present paper compares these two methods with the established Cyclotrac specific [125I]RIA (radioimmunoassay) using both commercial CsA-spiked control material as well as a group of 60 patient specimens (predominantly renal transplants). While each of the new methods showed acceptable precision and accuracy with the commercial quality control material, significant differences were demonstrated with patient specimens, such that FPIA was 12.5% greater than [125I]RIA (p less than 0.0001), which was in turn 5.9% greater than EMIT (p = 0.007). These data suggested that the FPIA may have residual CsA-metabolite interference and that the EMIT method was the most "specific" for parent CsA of the three tested, potentially therefore more comparable to high-performance liquid chromatography (HPLC).

High-performance liquid chromatographic determination of sotalol in plasma. I. Application to the disposition of sotalol enantiomers in humans

Two high-performance liquid chromatographic analytical methods have been developed for the measurement of dl-sotalol or d-sotalol and l-sotalol in plasma, using dl-atenolol as internal standard. Quantitation of dl-sotalol was carried out, following solid-phase extraction, on a 5-microns C18 reversed-phase column, with a mobile phase containing acetonitrile, ion-pairing reagent and distilled water, using ultraviolet detection at 235 nm. Quantitation of d-sotalol and l-sotalol was based on derivatisation with the chiral agent S-(-)-alpha-methylbenzyl isocyanate, followed by chromatographic separation on a 3-microns C18 reversed-phase column, with a mobile phase containing methanol, glacial acetic acid and distilled water, with fluorimetric detection at 220 nm excitation and 300 nm emission. A preliminary application of the latter method suggests that the disposition of sotalol in humans is not enantioselective.

Stereoselective inhibition of pindolol renal clearance by cimetidine in humans

There are few data on whether differences exist in the renal tubular secretion of enantiomers and no data on whether inhibition of renal secretion of individual enantiomers is stereoselective. Pindolol was used as a probe drug because it is used clinically as a racemic mixture of R-(+) and S-(-) enantiomeric forms and is highly secreted by the proximal tubules of the kidney. Eight young healthy subjects received a single 15 mg oral dose of racemic pindolol with and without 400 mg cimetidine twice daily. The area under the plasma concentration-time curve of both R-(+)- and S-(-)-pindolol were significantly (p less than 0.01) increased by cimetidine from 234 +/- 90 (mean +/- SD) to 344 +/- 78 ng/ml.hr for R-(+)-pindolol and from 209 +/- 73 to 288 +/- 69 ng/ml.hr for S-(-)-pindolol. The renal clearance of R-(+)-pindolol (170 +/- 55 ml/min) was significantly (p less than 0.05) less than that for S-(-)-pindolol (222 +/- 66 ml/min). Cimetidine significantly (p less than 0.01) reduced the renal clearances of R-(+)-pindolol to 104 +/- 18 ml/min and for S-(-)-pindolol to 155 +/- 38 ml/min. The enantiomer with the higher renal clearance [S-(-)-pindolol] had its renal clearance reduced less by cimetidine (26% versus 34%, p less than 0.05). Cimetidine appears to have a stereoselective action on the active transport system for organic cations in the proximal tubule.

Unbound plasma phenytoin concentrations measured using enzyme immunoassay technique on the cobas MIRA analyser--in vivo effect of valproic acid

This communication describes a modification of the total plasma phenytoin enzyme immunoassay technique (EMIT) run on the Cobas MIRA analyser that allows quantitation of unbound phenytoin concentrations in human plasma for routine therapeutic drug monitoring (TDM) purposes. An application of this method is also presented to consider the previously described protein binding drug interaction with concomitantly administered valproic acid in patients with epilepsy. The coefficients of variation for the unbound phenytoin assay ranged from 7.5 to 9.6% and the assay had a reproducibility and accuracy similar to the total phenytoin assay, acceptable for routine TDM. Phenytoin protein binding was linear over a range of total plasma concentrations of 3-65 mg/L. Patients also receiving valproic acid (nine patients, 105 specimens) had a significantly (p less than 0.0001) greater mean +/- SD unbound phenytoin fraction (13.3 +/- 3.1%) compared to nine patients (110 specimens) not receiving valproic acid (8.3 +/- 1.6%). There was also a significant correlation (p less than 0.001) between plasma valproic acid concentration and unbound phenytoin fraction, which resulted in greater intrasubject variability in phenytoin protein binding.

Renal tubular transport of morphine, morphine-6-glucuronide, and morphine-3-glucuronide in the isolated perfused rat kidney

The isolated perfused rat kidney was used to examine the renal handling of morphine and its inactive metabolite morphine-3-glucuronide (M3G), and active metabolite morphine-6-glucuronide (M6G). The kidneys were perfused with Krebs-Henseleit buffer (pH 7.4) containing albumin, glucose, and amino acids, and drug concentrations were measured by high performance liquid chromatography. There was no conversion of morphine to the glucuronides or deconjugation of M3G or M6G. At an initial morphine concentration of 100 ng/ml, the unbound renal clearance to glomerular filtration rate ratio (CLur/GFR) was 5.5 +/- 3.2 (mean +/- SD), indicating that net tubular secretion of morphine occurred. In the presence of M3G (2000 ng/ml) and M6G (500 ng/ml) this Clur/GFR ratio was elevated to 17.3 +/- 4.8 (p less than .001), which implicates an interaction between these compounds at an active reabsorption transport system. The CLur/GFR ratio for M3G at 2000 ng/ml was 0.90 +/- 0.04, indicating the possibility of a small component of tubular reabsorption, and this ratio was not significantly altered in the presence of morphine and M6G. M6G was reabsorbed, probably actively, to a greater extent than M3G, with an initial CLur/GFR ratio of 0.67 +/- 0.04, which was not affected when morphine and M3G were coadministered. These data demonstrate an unusual phenomenon in that the glucuronide metabolites, which are larger and less lipophilic than the parent drug morphine, undergo net tubular reabsorption. The renal handling of morphine is a complex combination of glomerular filtration, active tubular secretion, and possibly active reabsorption.

In vivo covalent binding of clofibric acid to human plasma proteins and rat liver proteins

Recent studies have shown that acyl-glucuronide conjugates are chemically reactive electrophilic metabolites that can undergo transacylation reactions resulting in intra-molecular rearrangement, hydrolysis and covalent binding of aglycone to albumin both in vitro and in vivo. The hypolipidaemic agent clofibrate is eliminated almost entirely as clofibric acid glucuronide in humans and rats. The formation of clofibric acid-protein adducts was investigated in 14 patients receiving 0.5-2.0 g/day of clofibrate for hypercholesterolaemia, and in liver homogenates from 20 rats administered 280 mg/kg/day of clofibric acid for up to 21 days. Total clofibric acid concentrations in the patients ranged from 0 to 114 mg/L. Covalently bound clofibric acid-protein adducts were detected in all patients, even in one subject in whom there was no measurable plasma clofibric acid. Concentrations ranged from 2.2 to 53.4 ng/mg protein and, in eight patients receiving 1.0 g/day of clofibrate, were correlated (P less than 0.05) with renal function as assessed by creatinine clearance. Clofibric acid-protein adducts were also present in rat liver homogenates, and increased with increasing duration of treatment (P less than 0.0001), from a mean (SE) of 10.1 (0.7) to 32.3 (1.6) ng/mg protein. The covalent binding of drugs to tissue macromolecules has traditionally been associated with toxicity. Further research is required to elucidate the role of acyl-glucuronide conjugates in the formation of drug-protein adducts and their biological consequences.

Improved high-performance liquid chromatography assay for atenolol in plasma and urine using fluorescence detection

An improved assay for racemic atenolol (AT) concentrations in human plasma and urine is described using a high-performance liquid chromatographic method with fluorescence detection. The method has a sensitivity limit of 0.5 micrograms/L in plasma with acceptable within- and between-run reproducibilities, and demonstrated linearity at concentrations up to 2,000 micrograms/L. A pilot clinical evaluation of the assay was undertaken on 56 trough plasma specimens from 36 outpatients on established AT therapy. Atenolol concentrations in these patients showed large variations at all prescribed doses, including undetectable levels in four patients (revealing unsuspected noncompliance). Because of its sensitivity and applicability to urinary analysis, the method can be used for pharmacokinetic studies and, under certain circumstances, may be valuable in clinical therapeutic drug monitoring.

Effect of renal dysfunction on the individual components of the acyl-glucuronide futile cycle

Drugs which are cleared predominantly by forming acyl-glucuronides undergo a futile cycle in which plasma drug clearance is a function of the formation, hydrolysis and renal clearance of the glucuronide conjugate. The effect of impaired renal function, induced by uranyl nitrate administration, on each component of this process was studied in rabbits using diphenylacetic acid. Uranyl nitrate administration produced a decrease in creatinine clearance of approximately 70% and diphenylacetic acid plasma clearance of approximately 35%. In healthy rabbits the primary determinant of diphenylacetic acid net clearance was the very large component of glucuronide renal clearance (14.10 ml/min/kg) compared with glucuronide formation (4.79 ml/min/kg) or glucuronide hydrolysis (2.56 ml/min/kg). Uranyl nitrate treatment reduced both creatinine clearance and the glucuronide renal clearance by approximately 70%. Renal dysfunction had little effect on the hydrolysis clearance of the glucuronide, but reduced its formation clearance by 22.8%. The reduction in plasma clearance of diphenylacetic acid was a function of both the decrease in glucuronidation (60% contribution) and the decrease in renal clearance of the glucuronide (40% contribution). This study supports the futile cycle mechanism of reversible glucuronide conjugation for acyl-glucuronides in general, and provides a mechanism for the impairment of the plasma clearance in renal failure of drugs forming acyl-glucuronides.

The disposition of ketoprofen enantiomers in man

1. The disposition of ketoprofen enantiomers was studied in 21 patients taking racemic ketoprofen (Orudis SR). 2. In each patient the plasma concentrations of the R- and S-enantiomers were similar at all times over a 24 h dosing interval. The mean (+/- s.e. mean) time-averaged plasma ketoprofen concentrations over the dosage interval were 0.76 (+/- 0.06) mg l-1 for R-ketoprofen and 0.78 (+/- 0.06) mg l-1 for S-ketoprofen. 3. Creatinine clearances for the 21 patients ranged from 6-162 ml min-1. There was no correlation between creatinine clearance and time-averaged plasma concentration for either R- or S-ketoprofen. 4. Approximately 30% of the dose was recovered in urine (unconjugated + glucuronide conjugate) and this was made up of 43% R-ketoprofen and 57% S-ketoprofen. Because of incomplete urine recoveries of ketoprofen it was not possible to determine whether inversion from the R- to the S-enantiomer takes place in man. 5. The data suggest that in terms of total (bound + unbound) ketoprofen, half the concentration value derived by a non-enantiospecific analysis would give a reasonable approximation of the pharmacologically active S-enantiomer concentration in plasma.

The stereospecific incorporation of fenoprofen into rat hepatocyte and adipocyte triacylglycerols

The formation of triacylglycerols containing fenoprofen was studied in rat isolated adipocytes and hepatocytes incubated with [3H]glycerol and R or S fenoprofen. In both hepatocytes and adipocytes there was a high-affinity enzymatic process for the synthesis of triacylglycerol containing fenoprofen which was stereospecific for the R enantiomer. The apparent Km values for R fenoprofen were 1.0 microM in adipocytes and 2.8 microM in hepatocytes. These results are consistent with the proposed stereospecific formation of R-2-arylpropionyl-CoA thioesters resulting in the stereospecific formation of R-tri-acylglycerol at clinically relevant unbound fenoprofen concentrations. In isolated hepatocytes, but not adipocytes, a second low-affinity enzymatic process for the synthesis of triacylglycerol containing fenoprofen was also observed. However, this process (Km = 3780 microM) occurred at concentrations much higher than those found in man with usual doses.

High-performance liquid chromatographic quantitation of triacylglycerols containing fenoprofen from biological samples

A normal-phase high-performance liquid chromatographic (HPLC) method has been developed for the quantitation of radiolabelled triacylglycerols containing fenoprofen, synthesized from [3H]glycerol by isolated hepatocytes and adipocytes. The assay consists of extracting the lipids into diethyl ether, separating triacylglycerols from polar endogenous lipids using silica Sep-Pak cartridges and quantitating endogenous triacylglycerols and triacylglycerols containing fenoprofen by HPLC resolution and scintillation counting. HPLC separation is achieved in less than 10 min. Using [14C]tripalmitin as internal standard the assay has a linear relationship between added triacylglycerol and measured endogenous triacylglycerols and triacylglycerols containing fenoprofen with regression coefficients of 0.997 and 0.998, respectively.

Enantioselective disposition of 2-arylpropionic acid nonsteroidal anti-inflammatory drugs. II. 2-Phenylpropionic acid protein binding

The binding of 2-phenylpropionic acid (2PPA) enantiomers to rabbit albumin has been studied using fatty-acid-free albumin, with and without oleic acid, and using plasma from control rabbits and from rabbits rendered uremic with uranyl nitrate. The models of binding examined included specific binding at one and at two species of binding site, nonspecific binding and with inhibition between enantiomers with competitive or noncompetitive kinetics. Although any one aspect of the data is adequately modeled by nonspecific binding together with a single species of specific site, the simplest physical model consistent with the whole data requires two species of specific site together with nonspecific binding. Oleic acid in vitro, or other modifiers in vivo, inhibit the binding at both specific sites and reduce nonspecific binding. The inhibition at one site is sufficient that the situation in whole plasma simplifies to one site plus nonspecific binding. Competition between enantiomers occurs at this remaining site, at which R-2PPA binds more avidly than S-2PPA. Both specific and non-specific binding are reduced further in uranyl nitrate-induced renal failure. In the light of these findings, we discuss the implications of enantioselective binding and of competition between enantiomers for binding sites on the interpretation of drug disposition studies.

Enantioselective disposition of 2-arylpropionic acid nonsteroidal anti-inflammatory drugs. I. 2-Phenylpropionic acid disposition

The disposition of 2-phenylpropionic acid (2PPA) enantiomers has been studied in 12 rabbits with normal renal function (control) and in 6 rabbits with renal dysfunction. In control animals a mean (S.E.M.) of 0.23 (0.02) of R-2PPA was inverted to S-2PPA, and the distribution volumes for unbound S- and R-2PPA were 0.30 (0.02) and 0.62 (0.07) liters/kg, respectively, but there was no evidence of stereoselectivity in the glucuronidation of R- or S-2PPA. A model was developed that predicted the fraction of the 2PPA in plasma present as unbound S-2PPA upon infusion of racemic 2PPA to steady state. The mean (S.E.M.) observed fraction was 0.69 (0.01) and the predicted fraction was 0.66 (0.03). Comparing the mean parameters of 2PPA disposition in renal dysfunction with those in the same animals during a control study, the fraction of R-2PPA undergoing inversion increased by 350%, the clearance of unbound S-2PPA decreased to 25% and the unbound clearance of R-2PPA by processes other than inversion decreased to 9% of the control means. These changes are consistent with the effects of renal dysfunction on acyl-glucuronide futile cycles for both R- and S-2PPA. Using the above data it can be calculated that, in an animal with severe renal dysfunction, upon an infusion of racemic 2PPA to steady state the concentration of the unbound S-enantiomer would be 5.6 times that in a control animal.

Enantiospecific high-performance liquid chromatographic analysis of 2-phenylpropionic acid, ketoprofen and fenoprofen

A high-performance liquid chromatographic method has been developed for the quantitation of the R- and S-enantiomers of 2-phenylpropionic acid, ketoprofen and fenoprofen. The assay consists of extracting the arylpropionic acid with an internal standard and measuring the total (R + S) concentration of enantiomers by reversed-phase chromatography, derivatising the chromatographic fraction corresponding to the enantiomers to form R- and S, R-2-phenylethylamide distereoisomers which are resolved by normal-phase chromatography in order to calculate the fraction of each enantiomer. The limits of sensitivity of the assay for 2-phenylpropionic acid, ketoprofen and fenoprofen are 6, 0.2 and 2.5 mg/l, respectively.

Cortisol does not inhibit prednisolone clearance

The disposition of prednisolone has been studied in eight male subjects with and without the concomitant administration of cortisol which produced plasma cortisol concentrations 10-fold higher than endogenous levels. The clearance and steady-state distribution volume of total prednisolone were increased as was the prednisolone free fraction but the clearance of unbound prednisolone was unaltered by cortisol co-administration.

Alterations in prednisolone disposition as a result of oral contraceptive use and dose

The disposition of total and free prednisolone has been studied in eight female subjects who used combined oestrogen-progestogen oral contraceptives and in eight female subjects who did not, each of whom received separate intravenous doses of 0.1 mg/kg (low) and 1.0 mg/kg (high) of prednisolone. Mean free prednisolone clearance was reduced congruent to 30% in oral contraceptive users compared to control subjects (P less than 0.001), the difference being greater for the low dose (39%) than for the high dose (24%). Pre-dose plasma cortisol concentrations were elevated two-fold (P less than 0.001) in oral contraceptive users compared to control subjects. These effects are consistent with a mechanism in which the competitive inhibition of free prednisolone clearance by cortisol contributes to the reduction of free prednisolone clearance by oral contraceptive use. Mean total prednisolone clearance and steady state distribution volume showed an approximate two-fold dose dependent increase consistent with a similar increase in plasma prednisolone free fraction (P less than 0.001). Free prednisolone clearance showed an 18% dose dependent decrease (P less than 0.001) but free steady-state distribution volume did not change with dose. At plasma prednisolone concentrations less than 400 ng/ml, prednisolone free fractions at any prednisolone concentration were greater after the low, than after the high dose. This effect is consistent with the displacement of prednisolone by cortisol from transcortin but not from albumin.

Alterations in prednisolone disposition as a result of time of administration, gender and dose

The disposition of total and free prednisolone has been studied in four male and four female volunteers, each of whom received an intravenous dose of 0.075 mg/kg (low) and 1.5 mg/kg (high) of prednisolone at both 06.00 h and 18.00 h. For the low dose, free prednisolone clearance was 14% lower (P = 0.012) and time-averaged prednisolone free fraction was 22% higher (P less than 0.001) in the morning, there being no circadian difference in total prednisolone clearance. There was no circadian differences in prednisolone disposition at the high dose. These findings are consistent with a mechanism in which cortisol causes a simultaneous competitive inhibition of prednisolone clearance and plasma protein binding at low, but not at high prednisolone doses. Prednisolone clearance was higher in female than in male subjects, the mean increase being 18% (P = 0.022) for total prednisolone and 21% (P = 0.036) for free prednisolone. Mean total prednisolone clearance and steady-state distribution volume were two-fold higher at the high vs the low dose (P less than 0.001), but free prednisolone clearance showed a dose dependent decrease of 11% (P = 0.019). There was no change in free prednisolone steady-state distribution volume.

A comparison of plasma methylprednisolone concentrations following intra-articular injection in patients with rheumatoid arthritis and osteoarthritis

Plasma concentrations of methylprednisolone following intra-articular injection were measured in rheumatoid arthritis and osteoarthritis patients. While substantial plasma concentrations were seen in both groups of patients there was no significant difference in the rate or extent of absorption of methylprednisolone from osteoarthritic or rheumatoid knees. This study suggests that it is the dissolution rate of the steroid formulation rather than the characteristics of the synovial membrane which determine rate and extent of systemic absorption of methylprednisolone after intra-articular injection.