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.

Pharmacodynamic monitoring of mycophenolic acid in rabbit heterotopic heart transplant model

Pharmacodynamic (PD) monitoring of immunosuppressive drugs provides a novel approach to optimization of drug therapy in transplant recipients. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. A comparison of the relationship between PD versus drug level monitoring was performed using a heterotopic cardiac transplant in New Zealand white rabbits. The animals were divided into four different treatment groups. Control animals were administered the drug vehicle, the treatment groups were administered mycophenolate mofetil (MMF) at doses of 40, 80, and 160 mg/kg/day. Statistically significant (p < 0.05) prolongation of graft survival was obtained at the 160 mg/kg/day dose group. The mean MPA concentration at this dose was approximately 2.5 mg/l, suggesting that this concentration may provide adequate immunosuppression. An increase in IMPDH activity appeared a few days prior to rejection, suggesting that measurement of enzyme activity may have potential for use as a marker of graft rejection. A significant (p < 0.05) relationship exists between MPA concentration and graft survival and the former with dose of MMF. There was a negative correlation (p = 0.17) between MPA concentration and IMPDH activity, while a trend (p = 0.37) to inverse relationship between graft survival and IMPDH activity was found. The data suggests that the measurement of the biological response may provide a useful adjunct to traditional therapeutic drug monitoring (TDM) for optimization of dosing of immunosuppressive drugs.

Effect of assay methodology on pharmacokinetic differences between cyclosporine Neoral and Sandimmune formulations

The new oral formulation of cyclosporine (CsA), Neoral (CsA-N), results in increased area under the curve (AUC) and decreased intra- and interindividual variation in blood concentrations and other pharmacokinetic (PK) parameters when compared with the current Sand-immune (CsA-S) formulation. The present study examines the effect of assay methodology on variability in blood concentrations and PK parameters for renal transplant patients receiving CsA-N and CsA-S and whether this variation is reduced with CsA-N. The results show that interindividual variations in PK parameters for patients receiving CsA-N were less than those for patients receiving CsA-S. Both blood concentrations and dose of CsA better correlated with abbreviated (4-h) AUC after administration of CsA-N. For both CsA-S and CsA-N, blood concentrations at 4 h postdose exhibited the best correlation with AUC. All samples were analyzed by three common procedures: HPLC, RIA, and fluorescence polarization immunoassay (FPIA). There were no significant differences observed in blood concentrations or PK parameters obtained from FPIA and RIA. HPLC results, however, were lower because of specificity of this method for the parent drug. The assay methodology did not have an effect on interindividual variability, indicating that the cross-reactivity of metabolites in commonly used immunoassays for CsA does not contribute to the PK variability observed in renal transplant patients.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression in renal transplant recipients

The combination of pharmacokinetic and pharmacodynamic monitoring of immunosuppressive drugs provides a novel method for the optimization of drug dosing. We chose to investigate this with the use of mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. The relationship between MPA concentration in plasma, IMPDH activity in whole blood, and nucleotide concentration in lymphocytes was investigated in renal-transplant recipients, who were randomized to receive either mycophenolate mofetil (MMF) (n = 5) or azathioprine (AZA) (n = 7), in combination with cyclosporine and prednisone. Blood samples were collected throughout the dosing interval. Pharmacokinetic analysis revealed substantial variability among the patients in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration of IMPDH activity in whole blood. The peak concentration of MPA achieved at 1 hr after dosing resulted in approximately 40% inhibition of IMPDH activity. As the MPA concentration decreased throughout the dosing interval, there was a gradual restoration of IMPDH activity. The inhibition of IMPDH activity (P < 0.05) in MMF-treated patients as compared with the AZA-treated controls was maintained for approximately 8 hr after dosing. No statistically significant (P > 0.05) difference between the predose and the 12 hr postdose activity was observed. The concentrations of guanine nucleotides, GDP and GMP, were significantly lower than in the AZA-treated group at most of the time points after dosing; however, considerable variability was observed. The measurement of the pharmacodynamic response to immunosuppressive drugs may provide not only a mechanism to predict the most appropriate dosing regimen, but also a viable alternative to traditional therapeutic drug monitoring, by assessing the overall state of immunosuppression.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measurement of inosine monophosphate dehydrogenase activity in a canine model

The combination of pharmacokinetic and pharmacodynamic (measurement of the biological effect) monitoring of immunosuppressive drugs provides a method for the optimization of drug dosing. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measurement of IMPDH activity in whole blood, the concentration required for 50% inhibition of IMPDH activity was approximately 200 mg/L (58 +/- 8.3% for whole blood [n = 6] and 55 +/- 10.0% for isolated lymphocytes). To ascertain the relationship between MPA concentration and IMPDH inhibition in vivo, dogs were administered a single dose of mycophenolate mofetil, the pro-drug of MPA, at 20 or 40 mg/kg orally. Pharmacokinetic analysis revealed that the Cmax of the 40-mg/kg group was statistically greater than that of the 20-mg/kg group (P < 0.05). There were no statistical differences in the other parameters investigated (area under the curve, beta half-life, mean residence time, volume of distribution at steady state, and clearance) between the two treatment groups. The half-life was calculated at approximately 8 hr for both dose groups. There was also substantial variability among the dogs in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration and IMPDH. Maximal inhibition of IMPDH activity of 30-40% occurs approximately 2-4 hr after dosing, followed by a gradual restoration in enzyme activity. After 24 hr, there is an increase in IMPDH activity that exceeds the pre-dosing levels in some cases by 3-fold. Evaluation of the pharmacokinetic and the pharmacodynamic responses to MPA in the canine model suggests that the drug should be administered ever 8 hr to optimize its immunosuppressive efficacy. This combined approach can be used for optimization of doses of this and other immunosuppressive drugs.

Therapeutic drug monitoring of cyclosporin G

Therapeutic drug monitoring has been an integral part of the clinical investigations of cyclosporin G (OG37-325 CsG), an analogue of cyclosporin A (CsA). In general, analytic approaches used for monitoring of CsA have been used for the measurement of CsG. However, the validity of this approach may be questioned, as there are significant differences between the two drugs in the areas of blood distribution, pharmacokinetics, steady-state concentration of metabolites, and biases with the various immunoassays adapted for measurement of the drug. Based on the above, it is not appropriate to assume that the therapeutic drug monitoring protocols previously established for CsA are applicable to CsG. The latter drug should be treated as a new compound, with the development of independent therapeutic monitoring guidelines. Similar approaches should be used for other immunosuppressive drugs.

Blood distribution and single-dose pharmacokinetics of leflunomide

Leflunomide (HWA 486, LEF) is a novel isoxazole derivative with potent immunosuppressive properties. LEF is converted to its active metabolite (A77 1726) after absorption. Presently, the blood distribution and pharmacokinetics of LEF have not been reported. Such information would prove invaluable in determining the appropriate medium for analysis and optimal immunosuppressive dosing regimes. In this study, A77 1726 was found to be primarily associated (> 95%) with the lipoprotein free fraction of plasma at all tested concentrations ranging from 0.4 to 100 mg/L. Detectable levels of A77 1726 (0.34 +/- 0.18 mg/L), analyzed by HPLC, were found in the plasma free fraction only at the highest tested concentration (100 mg/L). Single-dose pharmacokinetics of A77 1726 (i.v.) and HWA 486 (p.o.) were investigated in five healthy New Zealand white rabbits. The half-lives (t1/2) of A77 1726 i.v. and HWA 486 p.o. administration were 3.88 +/- 2.3 and 3.18 +/- 1.6 h, respectively. The volume of distribution by both routes of administration indicates minimal distribution into tissues (Vdss p.o. = 0.14 +/- 0.03 L/kg and Vdssi.v. = 0.09 +/- 0.02 L/kg). The mean residence time of A77 1726 was greater after oral administration of LEF (MRTp.o. = 10.54 +/- 2.6 h and MRTi.v. = 6.76 +/- 1.0 h). Identical areas under the curve suggest bioavailability was 100% (AUCp.o. = 421.16 +/- 204.5 mg.h/L and AUCi.v. = 399.75 +/- 126.9 mg.h/L).

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measuring IMP dehydrogenase activity

Pharmacodynamic monitoring of the biological effect of immunosuppressive drugs provides an alternative to traditional therapeutic drug monitoring. We chose this method to investigate mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by inhibition of IMP dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measuring IMPDH activity in whole blood, we found the concentration of MPA required for 50% inhibition of enzyme activity to be in the range of 2.0-5.0 mg/L for both human and rabbit blood. The amount of enzyme activity in whole blood depended on the concentration of the leukocytes, was unaffected by the type of anticoagulant used, and was stable in blood specimens stored for as long as 48 h at 4 degrees C. An inverse relationship was found between plasma MPA concentrations and IMPDH activity in rabbits administered a single dose of RS-61443, the prodrug of MPA. Maximal inhibition of IMPDH activity (by approximately 60%) occurs at peak concentrations of MPA; as the concentration of the drug decreases postdose, the enzyme activity gradually increases with little or no inhibition being observed 24 h postdose.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measuring IMP dehydrogenase activity

Pharmacodynamic monitoring of the biological effect of immunosuppressive drugs provides an alternative to traditional therapeutic drug monitoring. We chose this method to investigate mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by inhibition of IMP dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measuring IMPDH activity in whole blood, we found the concentration of MPA required for 50% inhibition of enzyme activity to be in the range of 2.0-5.0 mg/L for both human and rabbit blood. The amount of enzyme activity in whole blood depended on the concentration of the leukocytes, was unaffected by the type of anticoagulant used, and was stable in blood specimens stored for as long as 48 h at 4 degrees C. An inverse relationship was found between plasma MPA concentrations and IMPDH activity in rabbits administered a single dose of RS-61443, the prodrug of MPA. Maximal inhibition of IMPDH activity (by approximately 60%) occurs at peak concentrations of MPA; as the concentration of the drug decreases postdose, the enzyme activity gradually increases with little or no inhibition being observed 24 h postdose.

Measurement of the active leflunomide metabolite (A77 1726) by reverse-phase high-performance liquid chromatography

The immunosuppressive activity of leflunomide is expressed after conversion to its pharmacologically active metabolite A77 1726. Leflunomide is a potent immunosuppressant that inhibits both T-cell and B-cell activity. To date, no pharmacokinetic data have been reported on leflunomide or A77 1726, primarily because of lack of a suitable method for its analysis. We describe here the development and evaluation of a reverse-phase high-performance liquid chromatographic (HPLC) method for the analysis of A77 1726 in whole blood or plasma from humans or rabbits. In human blood, the method exhibited good analytic recoveries from 78 +/- 13.5% to 108 +/- 4.8% (mean +/- SD) for drug concentrations ranging from 400 to 100,000 micrograms/L. When using a sample volume of 0.25 ml the sensitivity of the method was found to be 400 micrograms/L, with a working standard range of up to 200,000 micrograms/L. The sensitivity of the method can be increased to 40 micrograms/L when 1.0 ml of sample is used. Between-run coefficients of variation of 12.2 and 14.7% at A77 1726 mean concentrations of 1,006 and 8,146 micrograms/L were found for this method. No significant differences in recovery of drug were noted when either human or rabbit plasma or whole blood was used as the medium of analysis. In whole-blood specimens, A77 1726 was found to be stable for up to 10 days at -20 or -70 degrees C.

Comparison of the efficacy, safety, and pharmacokinetics of controlled release and immediate release metoclopramide for the management of chronic nausea in patients with advanced cancer

BACKGROUND

The short elimination half-life of metoclopramide necessitates frequent administration for optimal relief of nausea. This study compares a newly developed controlled release preparation of metoclopramide (CRM) and immediate release metoclopramide (IRM) with respect to efficacy, safety, and pharmacokinetics in patients with chronic nausea associated with advanced cancer.

METHODS

Thirty-four patients with advanced cancer with nausea lasting more than 1 month and with no evidence of involvement of the gastrointestinal tract, peptic ulcer or gastritis, brain metastases, or metabolic abnormalities were randomized, in a double-blind cross-over study, to receive 40 mg of CRM every 12 hours or 20 mg of IRM every 6 hours for 3 days. Nausea, food intake, and side effects were assessed four times daily. On Day 3, sequential venous samples were taken (12 patients) to determine plasma metoclopramide concentrations.

RESULTS

In 29 evaluable patients, the intensity of nausea on Day 3, measured by a 0-100-mm visual analogue scale and 0-3 categoric scale was 15 +/- 17 and 0.6 +/- 0.6 after IRM, versus 8 +/- 9 (P = 0.033) and 0.4 +/- 0.5 (P = 0.055) after CRM, respectively. Visual analogue scale nausea scores recorded by time of day and by day for the 3 treatment days were significantly lower for patients who received CRM compared with those who received IRM (P = 0.047 and P = 0.043, respectively), but categoric nausea scores were not significantly different between treatments by time of day and by day across the 3 treatment days. No differences were observed in caloric intake or side effects between treatments. In a pharmacokinetic analysis, the CRM/IRM ratio for area under the curve0-12 (microgram x hours x L-1), Cmax (microgram/L), and Tmax (hours) was 100%, 98%, and 2.3 fold, respectively.

CONCLUSION

Controlled release metoclopramide is safe and effective in managing chronic nausea in patients with advanced cancer. Future studies should focus on characterizing this syndrome more clearly and on determining the optimal dose of metoclopramide and the effects of drug combinations that have proven to be useful in managing chemotherapy-induced emesis (i.e., metoclopramide plus corticosteroids).

Blood distribution of mycophenolic acid

RS-61443 (RS) a morpholinoethyl ester of mycophenolic acid (MPA), can be considered a prodrug, as immunosuppressive activity is expressed only after hydrolysis to MPA upon absorption. Little is known about the blood distribution of MPA; such information would have an impact on the medium used for analysis of the drug in clinical trials. This was investigated by spiking whole blood having an initial temperature of either 4 degrees or 22 degrees C with increasing amounts of MPA ranging from 100 to 10,000 micrograms/L. These drug concentrations span the range seen when immunosuppressive doses of the RS are administered. This was followed by incubation of the blood at 37 degrees C for 0-120 min prior to separation of the cells. The drug concentration was measured in the plasma and whole blood fractions by high-performance liquid chromatography. MPA was almost exclusively found in the plasma fraction and did not exhibit any temperature or concentration dependence. The free or unbound fraction of MPA over the same concentration range was determined by ultracentrifugation and demonstrated a concentration dependence ranging from 7.2 to 16.5% of total drug for a concentration range spanning 500-10,000 micrograms/L. The drug was found to be primarily associated with the non-albumin proteins in the plasma. Less than 10% of the drug was found to be bound to lipoproteins. The data suggest that from an analytical standpoint, plasma, rather than whole blood, would be the most suitable medium for analysis because of the higher concentrations of the drug found in this fraction.

EMIT cyclosporine assay: development of an application protocol for Technicon AXON System

Monitoring parent drug cyclosporine (CsA) concentrations in whole blood has been facilitated by the introduction of automated nonisotopic immunoassays [fluorescence polarization monoclonal whole blood assay (FPIA), EMIT Cyclosporine Assay]. The latter assay currently has a defined application only for Cobas Mira Chemistry Systems. The purpose of our work was to develop an application for this assay on the Technicon AXON. Instrument settings were optimized to arrive at the following assay performance characteristics. Limit of sensitivity was 50 micrograms/L. Interassay coefficients of variation (CV) were 11.2% (n = 16; mean = 81 micrograms/L) and 9.4% (n = 16; mean = 418 micrograms/L). Recoveries of 102, 112, and 117% were obtained by spiking aliquots of 10 whole blood patient pools of known CsA concentrations with 50, 100, and 200 micrograms/L CsA, respectively. Serial dilutions of two patient specimens demonstrated a linear relationship between expected and actual CsA concentrations (r = 0.996, 0.998; regression lines; y = 0.989x + 11.7; y = 0.979x + 9.5). Carryover and interference (lipemia) were not evident. Instrument calibration stability is at least 1 month. Comparison with CsA concentrations analyzed in renal transplant patients by the FPIA assay produced a linear regression equation of EMIT = 1.113x - 44.5, r = 0.968, Sy/x = 20.8, n = 32. Comparison with high-performance liquid chromatography (HPLC)-derived values in the same patient population produced a linear regression equation of EMIT = 1.114x - 16.4, r = 0.970, Sy/x = 20.2. FPIA-derived CsA concentrations averaged 14.2% more than those obtained with the EMIT method with the latter averaging 1.3% more than HPLC values.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of cyclosporine assays using sequential samples from selected transplant patients

The monitoring of cyclosporine (CsA) whole blood concentrations is an integral part of immunosuppressive treatment with this drug. Although such monitoring has been facilitated by the introduction of monoclonal immunoassay techniques, there is a paucity of published data comparing the assays longitudinally in selected patients. The purpose of our study was to co-evaluate two monoclonal immunoassays (Cyclosporine FPIA whole blood assay, Abbott Laboratories; Cyclo-Trac SP-whole blood RIA, Incstar Inc.) and a high-performance liquid chromatography (HPLC) technique for quantitating CsA in sequentially collected trough whole blood samples from 14 patients up to 75 days after renal (n = 6), heart (n = 3), and liver (n = 5) transplantation. HPLC CsA metabolite analyses (AM1, AM9, AM4N) were performed. Although CsA concentrations within most patients were significantly higher (p < 0.05, paired t test) when measured by both immunoassay techniques compared to HPLC, levels determined in three patients, (one liver, two renal) for the FPIA/HPLC comparison and one patient (liver) for the RIA/HPLC comparison were not significantly different (p > 0.05). CsA levels within nine patients were not significantly different (p > 0.05) when FPIA and RIA were compared, but results within three patients, (one liver, two renal) were significantly higher (p < 0.05) by RIA compared to FPIA, but results within one patient (heart) were significantly higher (p < 0.05) by FPIA. Our results demonstrate first that depending on the patient, HPLC-derived CsA results are not consistently lower than results generated by immunoassay techniques and second that CsA levels obtained by FPIA are statistically equivalent or in some patients, statistically less than RIA-derived levels.

Therapeutic monitoring of rapamycin: a new immunosuppressive drug

Rapamycin (RAPA) is a new immunosuppressive drug with a potency similar to that of FK506 and up to a 100-fold greater than that of cyclosporine (CsA). RAPA has shown to be efficacious in the prolongation of allograft survival in a number of animal models. In early studies, RAPA was administered on a dose/weight basis, with little attention given to its effective blood concentration. Details describing the approaches used to establish a therapeutic range for the drug in animal transplant models are described. Guidelines for therapeutic monitoring of the drug are proposed. It is hoped that such preclinical work in animals will facilitate establishment of monitoring protocols for the drug in clinical trials.

Single-dose pharmacokinetics of the new immunosuppressant RS-61443 in the rabbit

The pharmacokinetics of mycophenolic acid (MPA) were investigated in six New Zealand white rabbits following (i.v.) and (s.c.) administration of RS-61443. Plasma concentrations of MPA were analyzed by high-performance liquid chromatography (HPLC). Model-dependent and -independent parameters were calculated. Mycophenolic acid is rapidly cleared with a terminal half-life of approximately 1.0 h. The volume of distribution subsequent to i.v. administration indicates minimal distribution into tissues. The mean residence time and volume of distribution were greater for the s.c. as compared to the i.v. route of administration. The insignificant difference in the area under the curve between the two dosage routes infers that the bioavailability of RS-61443-derived MPA by the former route of administration is comparable to the latter. Trough concentrations at the doses administered are below the detection limit of the HPLC procedure. The implications of these findings in relation to the therapeutic monitoring of the drug are discussed.

Cross-reactivities of cyclosporin G (NVa2 cyclosporin) and metabolites in cyclosporin A immunoassays

Immunoassays of cyclosporin A (CsA) have been routinely used to measure CsG. We investigated the cross-reactivities of CsG and its metabolites, as well as the proportion CsG constitutes in relation to total drug measured, for six CsG metabolites (GM1, GM9, GM4N, GM1c, GM1c9, GM19) in the following CsA assays: Sandimmune selective RIA (SS), Sandimmune nonselective RIA (NS), Cyclotrac SP-RIA (CT), fluorescence polarization immunoassay (FPIA), and enzyme immunoassay (EMIT). The cross-reactivity of CsG in these assays was as follows: SS, FPIA, CT, approximately 100%; NS, approximately 40%; EMIT, &lt; 2%. The cross-reactivities of CsG metabolites were investigated in all assays except EMIT and varied among metabolites and assays. The most significant variance was found with the NS assay, where most of the metabolites exhibited cross-reactivities of &gt; 40%. In contrast, in the SS, FPIA, and CT assays, cross-reactivities of &lt; 5% were observed for most of the metabolites. The ranking of cross-reactivities of CsG metabolites in the assays is SS = CT &lt; FPIA &lt; NS. The degree of cross-reactivity did not change significantly when the SS, CT, and FPIA assays were calibrated with CsG instead of CsA--whether parent CsG was present or not. The data suggest that the SS, CT, and FPIA methods would be suitable for the routine monitoring of CsG.

Cross-reactivities of cyclosporin G (NVa2 cyclosporin) and metabolites in cyclosporin A immunoassays

Immunoassays of cyclosporin A (CsA) have been routinely used to measure CsG. We investigated the cross-reactivities of CsG and its metabolites, as well as the proportion CsG constitutes in relation to total drug measured, for six CsG metabolites (GM1, GM9, GM4N, GM1c, GM1c9, GM19) in the following CsA assays: Sandimmune selective RIA (SS), Sandimmune nonselective RIA (NS), Cyclotrac SP-RIA (CT), fluorescence polarization immunoassay (FPIA), and enzyme immunoassay (EMIT). The cross-reactivity of CsG in these assays was as follows: SS, FPIA, CT, approximately 100%; NS, approximately 40%; EMIT, < 2%. The cross-reactivities of CsG metabolites were investigated in all assays except EMIT and varied among metabolites and assays. The most significant variance was found with the NS assay, where most of the metabolites exhibited cross-reactivities of > 40%. In contrast, in the SS, FPIA, and CT assays, cross-reactivities of < 5% were observed for most of the metabolites. The ranking of cross-reactivities of CsG metabolites in the assays is SS = CT < FPIA < NS. The degree of cross-reactivity did not change significantly when the SS, CT, and FPIA assays were calibrated with CsG instead of CsA--whether parent CsG was present or not. The data suggest that the SS, CT, and FPIA methods would be suitable for the routine monitoring of CsG.

Clobazam and norclobazam quantitation in serum by capillary gas chromatography with electron-capture detection

We have developed a simple, rapid method for determination of the antiepileptic drug clobazam and its major active metabolite, norclobazam in serum. Serum (200 microL) made alkaline with sodium borate buffer is extracted with toluene. After evaporation of the organic layer and reconstitution with toluene, the extract is analyzed within 5 min by capillary gas chromatography (Hewlett Packard HP 5890A GC; 63Ni electron-capture detector; HP-5 column). Linear calibrations for clobazam and norclobazam (clobazam: r = 0.999; norclobazam: r = 0.997) have permitted automated integrator calculation of results. Imprecision and accuracy were evaluated using an in-house control. Intra- and interassay coefficients of variation (CV) were 6.2% (n = 10) and 9.8% (n = 21), respectively for clobazam and 5.7% (n = 10) and 6.3% (n = 21), respectively for norclobazam. The mean concentrations for clobazam and norclobazam in the control were 3.5 mumol/L and 8.7 mumol/L respectively, representing 106% and 100% of the weighed-in values. Simplicity, specificity, sensitivity, and rapidity are attributes that make this assay suitable for monitoring of clobazam and norclobazam in serum.

The Mexican asthma cure. Systemic steroids for gullible gringos

Asthmatic patients from western Canada and the United States have reported that after visits to an asthma clinic in Mexicali, Mexico, they return home substantially improved or cured having received "a bronchodilator medication unavailable in the United States or Canada because of the big drug companies." Analysis of these medications reveals that the most commonly prescribed combination is the glucocorticoid triamcinolone (unscored white tablets) and the antihistamine chlorpheniramine (coated biconvex orange or red tablets). Occasionally benzodiazepines are added to these medications. The patients are assured that the medications which they have been given are free of side effects and specifically, that corticosteroids are not used. Such therapy is dangerous to the patient who not only is unaware of the medications that he or she is taking, but is unlikely to mention this therapy to his or her physician. These patients risk drug interactions, medication side effects, and the possibility of adrenal failure either with a stress to their system or on withdrawal of drug treatment. Patients are also at risk of abandoning safer forms of asthma therapy for the miracle cure. We, too, are partially responsible for these unethical practices by avoiding the use of steroids and undertreating our patients at times, leaving them unnecessarily restricted and eager for any form of relief.

Rat brain concentrations of 5-hydroxytryptamine following acute and chronic administration of MAO-inhibiting antidepressants

Groups of male Sprague-Dawley rats were injected once daily with phenelzine (15 mg/kg) or tranylcypromine (10 mg/kg) and killed 6 h after drug administration on days 1, 2, 8 and 19. Brains were analyzed for MAO activity by a radiochemical procedure and for 5-HT concentrations by an electron-capture gas chromatographic procedure. Both drugs affected 5-HT concentrations in a similar manner--a significant increase of 5-HT over control levels by day 1, with levels still increasing between days 8 and 19, having attained concentrations approximately 5 times control values by day 19.

Theophylline toxicity--a consequence of congestive heart failure

A case is reported of an elderly patient with congestive heart failure (CHF), who was treated with juvenile oral doses of theophylline (Theo-Dur). The patient experienced toxic symptoms, and plasma concentrations were determined. A value of 60.6 micrograms/ml was reported and the theophylline administration was subsequently discontinued. Plasma concentrations and toxicity of theophylline are unpredictable in patients with CHF because of the great variability in clearance. This case demonstrates the necessity for careful monitoring of theophylline plasma levels in CHF patients.

Concomitant analysis of normetanephrine and 3-methoxytyramine in brain: a new gas-liquid chromatography procedure

A novel gas chromatographic procedure utilizing a glass capillary column and electron-capture detection is described for the simultaneous assay in brain of normetanephrine and 3-methoxytyramine, the 3-0-methylated metabolites or noradrenaline and dopamine respectively. The procedure has been used to quantitate these amines in whole rat brain and to demonstrate their post-mortem accumulation.

Effect of diphenhydramine on methaqualone metabolism: an in vitro study

A GLC assay to quantitate the methaqualone metabolite 2-methyl-3-(2-hydroxymethylphenyl)-4(3H)-quinazolinone was developed. Standard curves were linear, and recovery of the metabolite from tissue homogenates averaged 89%. In vitro metabolism of methaqualone by the 10,000Xg supernatant fraction of rat liver homogenate was measured by monitoring metabolite formation with the GLC assay. Diphenhydramine inhibited the in vitro metabolism of methaqualone. The percentage inhibition increased with increasing diphenhydramine concentration. The significance of this inhibition in relation to use and abuse of methaqualone--diphenhydramine combinations is discussed.

Simultaneous identification and quantitation of diphenhydramine and methaqualone

Methods for the simulataneous identification and quantitation of diphenhydramine and methaqualone in urine have been investigated. Suitable thin-layer and gas chromatographic techniques have been developed. The extraction techniques were evaluated by extracting human urine after the ingestion of therapeutic dosages of the two drugs. A charcoal cartridge technique proved to be superior to direct solvent extraction. Although enzyme hydrolysis gave slightly better recoveries than the charcoal cartridge technique, it is a time-consuming procedure.