Nonlinear kinetics and pharmacologic response to mibefradil

BACKGROUND

Increasing oral doses of mibefradil (10 to 320 mg) decrease its apparent oral clearance; however, intravenous doses up to 80 mg do not reduce its systemic clearance. This study aimed to understand the mechanisms underlying the zero-order kinetics of mibefradil.

METHODS

A group of 10 normotensive volunteers received 50 mg/day oral mibefradil for 8 days and, on days 1 and 8, 5 mg deuterated mibefradil by infusion. Ten additional volunteers observed the same protocol with a daily oral dose of 100 mg mibefradil. Serial blood samples were withdrawn, and mibefradil plasma concentrations were assayed by liquid chromatography-mass spectrometry. Blood pressure and heart rate were measured for 4 hours, and an ECG was performed 2 hours after drug administration.

RESULTS

Repeated oral administration of 50 mg mibefradil generated zero-order kinetics secondary to a decrease in mibefradil systemic clearance. Compared with the 50-mg dose, single and repeated oral doses of 100 mg further decreased mibefradil clearance. Mibefradil bioavailability was not affected by increasing mibefradil doses. Mean diastolic blood pressure was decreased by single and repeated doses of 100 mg to the same extent. Repeated doses of 100 mg reduced heart rate and prolonged the PR and QTc, changes that were associated with mibefradil plasma concentrations.

CONCLUSIONS

Repeated doses of 50 mg or doses of 100 mg mibefradil generated zero-order kinetics secondary to a decrease in hepatic extraction of the drug. Zero-order kinetics did not affect the response-concentration relationship of mibefradil.

Input rate as a major determinant of furosemide pharmacodynamics: influence of fluid replacement and hypoalbuminemia

To investigate how the response to a bolus and an infusion of furosemide is modulated by the rate of fluid replacement and by hypoalbuminemia, rabbits received 5 mg/kg of furosemide as a bolus or infused over 60 min, whereas diuresis was replaced with 13, 121, or 238 ml/h NaCl 0.9%/glucose 5% (50:50). Natriuretic and diuretic efficiencies were greater with the infusion than with the bolus of furosemide. Fluid replacement increased natriuretic and diuretic efficiency of furosemide bolus but only diuretic efficiency of furosemide infusion. Furosemide net fluid depletion reached a plateau when fluid replacement increased beyond 121 ml/h. Repeated plasmapheresis decreased plasma albumin by 30% (P <.05) and increased furosemide unbound fraction (P <.05). Compared with control rabbits, hypoalbuminemia decreased the natriuresis of the bolus (22.7 +/- 1.5-16.6 +/- 1.3 mmol, P <.05) but not that elicited by furosemide infusion (26.2 +/- 1.8 mmol). Given as a bolus, furosemide natriuretic and diuretic response as a function of its urinary rate of excretion exhibited an hyperbolic relationship, and after its infusion a clockwise hysteresis, denoting tolerance. Plasma renin activity was increased by the bolus and the infusion of furosemide, even in the presence of 121 ml/h of fluid replacement. It is concluded that: 1) the increase in natriuretic/diuretic efficiency of the bolus induced by fluid replacement is greater than when furosemide is infused, 2) furosemide net effect does not increase proportionally to fluid replacement, and 3) the infusion of furosemide prevents the hypoalbuminemia-induced decrease in response of furosemide given as a bolus.

Acute and chronic role of 5-HT3 neuronal system on behavioral and neuroendocrine changes induced by intravenous cholecystokinin tetrapeptide administration in humans

The influence of single and multiple oral doses of ondansetron, a selective 5-HT3 receptor antagonist, was evaluated against placebo on cholecystokinin tetrapeptide (CCK-4)-induced behavioral and neuroendocrine changes in humans. As compared to placebo, subjects receiving acute ondansetron treatment showed a significant decrease in the sum intensity of CCK-4-induced-panic symptoms (iPSS). Pre-CCK-4 neuropeptide Y (NPY) plasma levels were significantly higher and maximal changes in cortisol, growth hormone, and prolactin secretion from baseline (delta max) were significantly lower in the ondansetron group. After ondansetron and placebo chronic administration, there were no statistical differences in the iPSS between groups. Pre-CCK-4 NPY plasma levels were significantly higher; whereas, delta max for NPY significantly lower in the ondansetron group as compared to placebo. These results suggest a role for the 5-HT3 receptor in the neurobiology of panic disorder through a possible interaction with CCK and NPY systems. Ondansetron chronic effect on CCK-4-induced behavioral changes needs further exploration.

Effect of oral ondansetron on total cholecystokinin plasma levels following CCK-4 panic challenge procedure in healthy men

OBJECTIVE

To gain insight into whether ondansetron treatment induces changes in total cholecystokinin (CCKT) plasma levels before and after administration of the cholecystokinin tetrapeptide (CCK-4) panic challenge procedure in healthy men.

METHODS

Thirty-eight volunteers received a 50-microgram bolus of CCK-4 60 minutes after a single oral dose (acute treatment) and multiple oral doses (chronic treatment) of ondansetron or placebo.

RESULTS

Results showed no difference in CCKT plasma levels of CCKT elimination rate constant between the ondansetron and the placebo groups after either acute or chronic treatment.

CONCLUSION

Results from this study suggest that total CCK plasma levels are not influenced by either acute or chronic treatment with ondansetron. However, the effect of ondansetron on the different CCK component fractions still needs exploration.

[A metastatic neuroendocrine tumor with exceptional outcome!]

INTRODUCTION

Neuroendocrine tumors are rare, with poor prognosis when not or poorly differentiated.

EXEGESIS

The authors report the case of a patient who presented with a metastatic poorly differentiated neuroendocrine tumor that was resistant to chemotherapy. The different sites of the carcinoma were lung, pancreas, kidney and lymph nodes. The patient received no treatment and complete spontaneous remission appeared after 21 months. This remission has been lasting for five years.

CONCLUSION

It is the first case of spontaneous remission of a metastatic poorly differentiated neuroendocrine tumor. The evolution and classical sites of neuroendocrine tumors are reviewed. Renal metastasis is also unusual. This report illustrates the fact that neuroendocrine tumors are heterogeneous.

Plasma levels of nicotine and safety of smokers wearing transdermal delivery systems during multiple simultaneous intake of nicotine and during exercise

Although transdermal nicotine patches have been studied extensively under recommended conditions, the present studies were designed to assess the nicotine plasma levels and the safety of transdermal nicotine patches in smokers undergoing situations suspected to result in increased nicotine plasma levels. The first study examined the effects of increasing nicotine intake through sequential administration of a nicotine patch (day 2), a patch followed by consumption of nicotine gum (day 3), and a patch followed by gum consumption and cigarette smoking (day 4). In this study, nicotine plasma levels increased transiently after the addition of each nicotine source. Mean areas under the concentration-time curves from 0 to 24 hours (AUC0-24) for nicotine were 453 +/- 120 ng.hr/mL (day 2), 489 +/- 143 ng.hr/mL (day 3), and 485 +/- 143 ng.hr/mL (day 4). The second study evaluated the effects of physical exercise on the kinetics and the safety of two different types of nicotine transdermal devices: Nicoderm and Habitrol. The mean delivered dose of nicotine was higher with Nicoderm compared with Habitrol, and the two products were not considered to be bioequivalent. During a 20-minute exercise period, nicotine plasma levels increased by 13 +/- 9% for Nicoderm and 30 +/- 20% for Habitrol. This increase in nicotine plasma levels was probably related to the exercise-induced increase in peripheral circulation at the patch site. Results from both studies indicate a clinically nonsignificant increase in blood pressure and heart rate after the administration of nicotine. After exercise, subjects taking Habitrol tended to have a higher incidence of adverse events compared with baseline values. Safety profiles remained acceptable in both studies despite the increases in nicotine plasma levels. It was concluded that both superimposed nicotine sources and physical exertion result in short-lived plasma nicotine elevations and temporarily increase nicotine pharmacodynamic parameters without increased risk to the volunteers.

High-resolution liquid chromatographic method using ultraviolet detection for determination of ondansetron in human plasma

This paper describes a simple technique for extraction and a sensitive high-performance liquid chromatographic method for separation and quantitation of ondansetron in human plasma. The procedure involved liquid-liquid extraction of ondansetron from plasma, reversed-phase HPLC separation and ultraviolet detection at 305 nm. The internal standard method was applied for quantitation. The recovery of ondansetron was >85%. Linearity was good throughout the concentration range anticipated in human plasma from investigations in panic disorder (0.5-15 ng/ml, r2 ranging from 0.9953 to 0.9988). This method was applied to the determination of plasma concentrations of ondansetron in humans.

Quantification of ketoprofen enantiomers in human plasma based on solid-phase extraction and enantioselective column chromatography

An HPLC method for the quantification of ketoprofen enantiomers in human plasma is described. Following extraction with a disposable C18 solid-phase extraction column, separation of ketoprofen enantiomers and I.S. (3,4-dimethoxy benzoic acid) was achieved using a chiral column [Chirex 3005; (R)-1-naphthylglycine 3,5-dinitrobenzoic acid] with the mobile phase, 0.02 M ammonium acetate in methanol, set at a flow-rate of 1.2 ml/min. Baseline separation of ketoprofen enantiomers and I.S., free from interferences, was achieved in less than 20 min. The calibration curves (n = 14) were linear over the concentration range of 0.16 to 5.00 micrograms/ml per enantiomer [mean r2 of 0.999 for both enantiomers, root mean square error were 0.015 for R(-) and 0.013 for S(+)]. The inter-day coefficient of variation for duplicate analysis of spiked samples was less than 7% and the accuracy was more than 93% over the over the concentration range of 0.2 to 4.0 micrograms/ml for individual enantiomer using 1 ml of plasma sample. This method has been applied to a pharmacokinetic study from healthy human volunteers following the administration of a ketoprofen extended release product (200 mg). This method is simple, fast and should find wide application in monitoring pharmacokinetic studies of ketoprofen.

Organ-specific pattern of inhibition of diltiazem metabolism at steady state in rabbits

Plasma levels of diltiazem, after its chronic administration, are usually higher than predicted. Because several organs contribute to diltiazem metabolism, this study aimed to determine the effect of an infusion of diltiazem to steady state on the ability of the intestine, liver and lungs to metabolize diltiazem and its metabolites N-desmethyldiltiazem (MA) and desacetyldiltiazem (M1). The kinetics of diltiazem were assessed after a single i.v. injection (2 mg/kg) and after an infusion (1.4 mg/kg/hr over 15 hr) of diltiazem. After serial blood sampling, the rabbits were sacrificed, and diltiazem, MA and M1 constant rates of metabolism (Kmet) were estimated in the 10,000 x g supernatants of the intestinal mucosa, liver and lungs. In vivo, the systemic clearance of infused diltiazem was lower than that estimated after i.v. injection of diltiazem, i.e., 54.4 +/- 2.4 vs. 70.3 +/- 5.8 ml/min/kg (P < .05). In vitro, diltiazem Kmet was reduced in liver homogenates from rabbits that had received the infusion of diltiazem, but not in the intestine or lungs. Moreover, the production of MA was reduced in liver homogenates and that of M1 in intestinal and lung homogenates. The Kmet of MA was not affected by the infusion of diltiazem in any tissue studied; however, the Kmet of M1 was reduced by the infusion in the three tissues tested. It is concluded that, in rabbits, long-term administration of diltiazem leads to an accumulation of diltiazem primarily because its N-demethylation is decreased in the liver, in addition, the demethylation of M1 is reduced in the small intestine, liver and lungs.

First-pass metabolism of diltiazem in anesthetized rabbits: role of extrahepatic organs

PURPOSE

The aim of this study was to assess in vivo which organs contribute to the first-pass metabolism of diltiazem.

METHODS

Anaesthetized rabbits received diltiazem into the thoracic aorta (TA) ( 1mg/kg), jugular vein (JV) (2 mg/kg), portal vein (PV) (4 mg/kg) or small intestine (SI) (5 mg/kg). Serial blood samples were withdrawn from the abnormal aorta to assay diltiazem, N-demethyl-diltiazem (MA) and deacetyldiltiazem (M1).

RESULTS

The area under diltiazem plasma concentration curve/time (AUC0-infinity) normalized by the dose was AUCTA approximately equal to AUCJV > AUCPV > AUCSI: Intestinal and hepatic diltiazem availability was 43 and 33%, respectively. The systemic availability of oral diltiazem was 12%. Diltiazem given into the SI and PV generated primarily MA, and injected into the JV and TA produced mainly M1.

CONCLUSIONS

In rabbits, the intestine and the liver contribute to the first-pass metabolism of diltiazem, and the amount and species of metabolites generated depend upon the route of administration of diltiazem.

Lack of presystemic metabolism of nifedipine in the rabbit

In humans, oral bioavailability of nifedipine has been reported to be around 60%, although the organ(s) contributing to its first-pass metabolism have not been determined. The aim of this study was to determine in vivo, in anesthetized and conscious rabbits the role of the intestine, liver, and lungs in the first-pass metabolism of nifedipine. To assess the extraction of nifedipine by the intestine, liver, and lungs, nifedipine was administered before and after each organ, and serial blood samples were withdrawn from an artery. In conscious rabbits, the systemic clearance of nifedipine injected into a lateral vein of an ear was 14.6 +/- 1.6 ml/min per kg, a value that was slightly decreased by anesthesia. In anesthetized rabbits, compared to the clearance estimated when nifedipine was administered into the thoracic aorta, the administration of nifedipine into a jugular vein, into the portal vein, or into the portal vein, or into the duodenum did not increase the value of the systemic clearance. In conscious rabbits, the clearance of nifedipine estimated when the drug was administered into the duodenum, the peritoneum, the portal vein, or into the jugular vein was identical to the clearance calculated when the drug was injected into the thoracic aorta. In vitro, nifedipine was metabolized in liver and intestinal epithelial cells homogenates but not in lungs or kidneys. We concluded that in the rabbit, oral nifedipine is not subjected to a first-pass metabolism, even though the intestine and the liver may contribute to nifedipine systemic clearance.

The site of absorption in the small intestine determines diltiazem bioavailability in the rabbit

PURPOSE

Since the ability of the small intestine to biotransform a drug may decrease in distal segments of the intestine, this study aimed to assess whether the site of administration in the small intestine could affect the systemic bioavailability of diltiazem and its two active metabolites, N-desmethyldiltiazem (MA) and desacetyl-diltiazem (M1).

METHODS

Five mg/kg of diltiazem were administered into the lumen of the proximal (0-30 cm, n = 9) or the distal (150-180 cm) small intestine (n = 7) of anesthetized New Zealand rabbits. Blood samples were drawn from the femoral artery for 6 hours, and diltiazem, MA and M1 were assayed by HPLC.

RESULTS

The area under the curve (AUC0-->infinity) of diltiazem administered into the distal small intestine was larger than that estimated when diltiazem was given in the proximal segment (14.20 +/- 2.82 vs 8.14 +/- 0.88 micrograms.min/ml, p < 0.05), due to a lower diltiazem oral clearance (440 +/- 78 vs 660 +/- 55 ml/min/kg, p < 0.05). The AUC0-->360 of MA was not affected by the site of diltiazem administration, but the AUC0-->360 of M1 was increased when diltiazem was administered in the distal segment of the small intestine. When administered into the distal segment of the intestine, the molar sum of diltiazem and its active metabolites was 48% greater than when delivered into the 0-30 cm segment of the small intestine; as a consequence, absorption of diltiazem in distal segments of the small intestine may enhance its pharmacological response.

CONCLUSIONS

The site of absorption into the intestine modulates the bioavailability of diltiazem and its two active metabolites.

Safety, tolerability, and pharmacokinetic actions of diltiazem in pediatric liver transplant recipients on cyclosporine

Thirty-two children who had undergone liver transplantation were paired according to their posttransplantation duration, renal function, and diagnoses when possible and randomized either to continue nifedipine (NIF group) or switch to diltiazem (DIL group), in addition to continuing their usual immunosuppressive medications. The cases were followed prospectively regarding diltiazem tolerance, cyclosporine dose requirements, effect on cyclosporine kinetics, diltiazem kinetics, as well as effect on renal function. Diltiazem was well tolerated at a dose of 3 mg to 6.4 mg/kg/day (max 180 mg/day) with infrequent self-limited mild side effects. Cyclosporine daily dose was reduced by a mean of 36.7% and 38.3% at 3 and 6 months, respectively, in the DIL group to achieve target trough cyclosporine levels without modifying liver function. No significant difference in renal function was observed after 3 to 6 months in either group based on blood urea nitrogen and creatinine levels and glomerular filtration rate by the DTPA method. Diltiazem appears to be well tolerated in children and allows for substantial dose reductions of CSA without apparent effects on liver graft function.

Stereospecific high-performance liquid chromatographic assay of ketoprofen in human plasma and urine

A high-performance liquid chromatographic (HPLC) assay suitable for the analysis of the enantiomers of ketoprofen (KT), a 2-arylpropionic acid (2-APA) non-steroidal antiinflammatory drug (NSAID), in plasma and urine was developed. Following the addition of racemic fenoprofen as internal standard (I.S.), plasma containing the KT enantiomers and I.S. was extracted by liquid-liquid extraction at an acidic pH. After evaporation of the organic layer, the drug and I.S. were reconstituted in mobile phase and injected into the HPLC system. The enantiomers were separated at ambient temperature on a commercially available 250 x 4.6 mm amylose carbamate-packed chiral column (Chiralpak AD) column with hexane-isopropyl alcohol-trifluoroacetic acid (80:19.9:0.1, v/v/v) as the mobile phase pumped at 1.0 ml/min. The enantiomers of KT were quantified by ultraviolet detection with the wavelength set at 254 nm. The assay described allows for the direct quantitation of KT enantiomers without pre-column derivatization, and is suitable for clinical studies of KT enantiomers in human plasma and urine after administration of therapeutic doses.

Metabolism of diltiazem in hepatic and extrahepatic tissues of rabbits: in vitro studies

Diltiazem (DTZ) is a calcium channel blocker widely used in the treatment of angina and hypertension. DTZ undergoes extensive metabolism yielding several metabolites, some of which are active like N-desmethyldiltiazem (MA), desacetyldiltiazem (M1) and N-desmethyl,desacetyldiltiazem (M2). Due to the nature of its biotransformation, several organs should have the ability to metabolize DTZ, however it is still assumed that the liver is the only organ implicated in its elimination. In this study, the fate of DTZ, MA and M1 was assessed in several organs that could contribute to their biotransformation. To this purpose, DTZ (48.2 microM) was incubated in the 10,000 x g supernatant of homogenates of rabbit tissues for 60 min at 37 degrees C. Multiple samples were withdrawn, and DTZ and its metabolites were assayed by HPLC. The elimination rate constant of DTZ in 10,000 x g supernatants varied between the organs: liver 334 +/- 45, proximal small intestine 69 +/- 11, distal small intestine 25 +/- 3, lungs 15 +/- 6 and kidneys 8 +/- 6 (10(-4) min-1). The metabolism of DTZ in the liver generated large amounts of MA but no M1, and in the small intestine, modest amounts of both metabolites. When MA (50.0 microM) or M1 (53.7 microM) were incubated in liver homogenates, the estimated elimination rate constant were 166 +/- 23 and 468 +/- 53 (10(-4) min-1), respectively. The rate of degradation of the metabolites in the small intestine was much slower.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereospecific high-performance liquid chromatographic assay of zopiclone in human plasma

A high-performance liquid chromatographic (HPLC) assay for the analysis of the enantiomers of zopiclone (ZPC), a cyclopyrrolone hypnotic, in plasma was developed. Following the addition of chlordiazepoxide as internal standard (I.S.), plasma containing the ZPC enantiomers and I.S. was extracted by liquid-liquid extraction at an alkaline pH. After evaporation of the organic layer, the drug and I.S. were reconstituted in ethanol-hexane (80:20, v/v) and injected onto the HPLC column. The enantiomers were separated at ambient temperature on a 25-cm Chiralcel OD-H column with ethanol-hexane (60:40, v/v) as the mobile phase pumped at a flow-rate of 0.6 ml/min. The enantiomers of ZPC were quantified by fluorescence detection with excitation and emission wavelengths of 300 and 470 nm, respectively. The assay described allows for the direct quantitation of ZPC without pre-column derivatization, and is suitable for clinical studies of ZPC in humans after administration of therapeutic doses.

Pharmacokinetics and pharmacodynamics of a slow-release formulation of diltiazem after the administration of a single and repeated doses to healthy volunteers

Diltiazem is a calcium antagonist used in angina pectoris and hypertension. There is little information concerning the slow-release (SR) formulation in the literature. The pharmacokinetics of diltiazem SR (120 mg) have been assessed over a 36h period in healthy volunteers after single- (SD) and multiple-dose (MD) administrations. Cmax, AUC0-36, and AUC0-infinity were significantly increased at steady state compared to the extrapolated SD values, suggesting accumulation of the drug. Renal and cardiovascular parameters have also been assessed at intervals of 3-6h during baseline (B) and following single and multiple doses of diltiazem SR. Diuresis over a 24 h period was increased, but not significantly, by the administration of diltiazem SR i.e. 1782 ml (MD) and 1915 ml (SD), versus 1626 ml (B). Natriuresis and creatinine clearance were slightly decreased by diltiazem SR, compared to B values; this might be due to the relatively short period over which steady state was maintained (five days) and the effects of norepinephrine and angiotensine II on renal vasculature and the pharmacokinetics of diltiazem SR. No increase in the systolic blood pressure occurred after the administration of diltiazem SR; diastolic blood pressure and PR interval were decreased and increased respectively by diltiazem SR. These results do not appear to be clinically significant. Finally, no relation was found between the pharmacokinetics and pharmacodynamics of diltiazem. This may be attributed to the absence of clinically significant effects in healthy volunteers, the presence of active metabolites, the pharmacokinetics of the SR formulation and/or the accumulation of the drug at steady state.

Clentiazem given at reperfusion improves subendocardial reflow and reduces myocardial infarct size in the dog

The postischemic cardioprotection by calcium antagonists and the interplay between neutrophils and regional myocardial blood flow were investigated further, using clentiazem, a new potent calcium channel blocker derived from diltiazem. A 90-min occlusion of the interventricular coronary artery was followed by 6 hr of reperfusion in anesthetized dogs. One group was given clentiazem: 100 micrograms/kg at 5 min before reperfusion followed by a perfusion of 1 microgram/kg/min until sacrifice; controls received saline. Infarct size (% of area at risk) estimated with triphenyltetrazolium staining and by histology was reduced by nearly 50% (P < .05) in treated (16.6 +/- 3.0%), as compared to control (31.6 +/- 6.3%) dogs. Regional and collateral myocardial flows estimated with radioactive microspheres were similar between groups before and during occlusion. However, after an initial recovery to preocclusion values at 30-min reperfusion in both groups, flow declined to 50% normal (P < .05) in control animals after 3 and 6 hr in midwall and subendocardium, but the change was remarkably attenuated (P < .05) in subendocardium of clentiazem-treated dogs. Also, neutrophil accumulation at the epicardial side of the infarct, at the edge of salvaged myocardium, and estimated by tissue myeloperoxidase measurement, was reduced by 50% in treated dogs (clentiazem: 17.2 +/- 2.8; controls: 32.3 +/- 2.7 x 10(6) neutrophils/g). We conclude that administration of clentiazem at reperfusion reduces infarct size by interfering with both neutrophil accumulation and development of subendocardial no reflow in reperfused myocardium.

Influence of drug formulation on drug concentration-effect relationships

Slow release formulations (SRFs) are developed on the basis that the response elicited by a drug is closely related to changes in its plasma concentrations. As a consequence, the drug in the SRF is considered bioequivalent to the same drug administered in a conventional or immediate release formulation (IRF). The available literature suggest that for drugs eliciting a simple response, i.e. theophylline, the response is not affected by the rate of input of drug into the systemic circulation. Therefore, the pharmacodynamics are closely related to the pharmacokinetics of the drug, which are independent of formulation. In this case, SRFs and IRFs are truly bioequivalent. The pharmacological effect of some drugs, e.g. nifedipine, prazosin, furosemide (frusemide), etc., triggers compensatory homeostatic mechanisms. Therefore, the measured effect may not directly relate to the plasma drug concentration. Furthermore, the characteristics of the response will be modulated by the rate of input of the drug, i.e. drugs in SRF will elicit a greater response because a slow input triggers fewer homeostatic reactions. As a consequence, for drugs that trigger homeostatic reactions, a drug released from an SRF may not be bioequivalent to the same drug released from an IRF. Finally, when tolerance to an effect develops, a drug administered as an SRF will elicit a smaller effect than when administered as an IRF. Therefore, even if the different formulations of a drug were bioequivalent on the basis of pharmacokinetic parameters, they would not be equivalent on the basis of pharmacodynamic factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative pharmacokinetics and pharmacodynamics of two marketed bid formulations of diltiazem in healthy volunteers

Cardizem SR and Bi-Tildiem were both approved in their respective countries on the basis of clinical trials demonstrating efficacy and safety in the treatment of angina pectoris. In this cross-over randomized study, we assessed whether these two sustained-release formulations of diltiazem have equivalent pharmacokinetic and pharmacodynamic profiles. Twenty-four young healthy male volunteers were hooked to Holters and ambulatory blood pressure monitors for 24 h to establish baseline systolic blood pressure (SBP), diastolic blood pressure (DBP), sinus rate and PR intervals. They then received a single dose of 120 mg of diltiazem from one formulation. The pharmacodynamic measurements were recorded for a further 24 h and blood samples were collected over 36 h for evaluation of diltiazem in plasma by a high-performance liquid chromatogrpahic (HPLC) method. The procedures were repeated with the alternate formulation after a 7 d wash-out. Pharmacokinetics showed statistically significant (p < 0.01) differences in AUC0-12 with means (+/- SD) of 519.2(+/- 172.8) and 429.6(+/- 147.2) ng h ml-1, AUC0-36 of 835.6(+/- 281.6) and 730.9 (+/- 271.5) ng h ml-1 and Cmax of 89.1(+/- 30.3) and 61.1(+/- 21.2) ng ml-1 for Cardizem SR and Bi-Tildiem, respectively. The only pharmacodynamic parameter showing a statistically significant difference in change from baseline between the two formulations was DBP with mean (+/- SD) change in AUC0-12 of -13.6(+/- 20.8) and +8.4(+/- 31.7) mm Hg h (p = 0.0135) and in AUC0-24 of -33.0(+/- 43.7) and -0.3(+/- 59.2) mm Hg h (p = 0.0463) for Cardizem SR and Bi-Tildiem, respectively. These findings suggest that assessment of efficacy of sustained-release formulations of diltiazem by bioequivalence could be misleading. They also confirm that a single dose of diltiazem does not elicit a significant pharmacodynamic response in healthy volunteers. Equivalence for such formulations should therefore be demonstrated by pharmacodynamic evaluation or clinical studies in a patient population.

Stereospecific high-performance liquid chromatographic assay of ibuprofen: improved sensitivity and sample processing efficiency

A high-performance liquid chromatographic (HPLC) assay suitable for the analysis of the enantiomers of the non-steroidal anti-inflammatory drug ibuprofen (IB) in plasma was developed. Following the addition of racemic fenoprofen as internal standard (I.S.), samples are acidified and extracted with a mixture of isooctane-isopropanol (95:5, v/v). After evaporation of the organic layer, the drug and I.S. are derivatized with S-(-)-1(1-naphthyl)ethylamine (S-NEA) after addition of ethyl chloroformate as the coupling reagent. Ethanolamine is added 3 min after the addition of S-NEA to react with the excessive ethyl chloroformate. The resultant diastereomers corresponding to IB and I.S. were chromatographed at ambient temperature on a 100 mm x 4.6 mm I.D. C18 reversed-phase column using acetonitrile-water-acetic acid-triethylamine (60:40:0.1:0.02) as the mobile phase pumped at a flow-rate of 1.2 ml/min. Detection of the fluorescent chromophore was at 280 and 320 nm for excitation and emission, respectively. The suitability of the assay for clinical pharmacokinetic studies of IB was determined by the analysis of plasma samples obtained from a healthy volunteer, following administration of a single 400-mg oral dose of racemic IB.

Bioavailability of metformin in tablet form using a new high pressure liquid chromatography assay method

Twenty-four young healthy volunteers received a single dose of metformin 500 mg (Glucophage, Nordic Laboratories, Canada) in tablet form. Plasma concentrations were determined by HPLC in samples collected prior to and 0.33, 0.66, 1, 1.33, 1.66, 2, 2.5, 3, 4, 5, 6, 7, 8, 10, 12, 15, 18, 24, and 30 h after dosing. Mean (+/- SD) Cmax was 682.1 (160.6) ng ml-1 at a mean (+/- SD) tmax of 2.4 (0.93) h. Overall elimination was monoexponential with a mean (+/- SD) half-life of 3.16 (0.47) h. We conclude that metformin is rapidly absorbed from this formulation and is also rapidly eliminated. Extrapolation to steady state predicts that equilibrium will be reached within 24 h.

Effect of congestive heart failure on clentiazem pharmacokinetics in a dog model

Clentiazem, 8-chloro diltiazem, is a calcium channel blocker currently undergoing evaluation for the treatment of stable angina and hypertension. As patients with ischaemic disorders often present some degree of heart failure, the aim of this study was to investigate the effect of congestive heart failure on clentiazem (200 micrograms kg-1, i.v. bolus) pharmacokinetics in a canine model. Congestive heart failure was induced in six dogs by rapid ventricular pacing (240 beats min-1) for 3-5 weeks. Clentiazem pharmacokinetics was studied in each dog under the control condition and after the development of clinical signs of heart failure (ascites, dyspnea, fatigue). Blood samples were collected up to 480 min post-dose. Clentiazem plasma concentrations were determined by high performance liquid chromatography. The area under the plasma concentration versus time curves (AUC0-infinity) was significantly increased in congestive heart failure dogs (8.8 +/- 1.6 vs 21.8 +/- 1.4 micrograms min ml-1) (mean +/- SEM). These changes were related to a reduction of the volume of distribution of the central compartment (0.9 +/- 0.1 vs 0.2 +/- 0.11 kg-1) and total body clearance (1.9 +/- 0.4 vs 0.7 +/- 0.21 h-1 kg-1). It is concluded that, in our model, congestive heart failure significantly modifies clentiazem disposition. These results suggest that caution should be exercised when clentiazem is given to patients with a low ejection fraction and a compromised cardiac function. Reduced loading and maintenance doses might be recommended in patients with severe congestive heart failure.

Pharmacokinetics of ibuprofen enantiomers after single and repeated doses in man

The pharmacokinetic parameters of ibuprofen enantiomers after a single 600 mg dose and repeated 3 x 400 mg doses of Nurofen were determined in 12 healthy volunteers. Terminal half-lives were similar for both enantiomers, but plasma levels of S-ibuprofen were higher than those of R-ibuprofen, due to the chiral inversion and differences in distribution and metabolism. Comparison of maximal concentrations and areas under the concentration vs time curves between the first and last doses for each enantiomer indicated linear pharmacokinetics with no time-dependency. A large inter-individual variability in the ratio of S- to R-ibuprofen average concentrations at steady-state was observed (mean +/- SD 1.89 +/- 0.89) and probably accounts for the known lack of correlation between racemic ibuprofen concentrations and therapeutic efficacy.

Effect of an acute dose of alcohol on the pharmacokinetics of oral nifedipine in humans

Pharmacokinetic and pharmacodynamic interactions of alcohol and nifedipine were assessed in 10 healthy human volunteers. Doses of 20 mg (2 x 10-mg capsules) of nifedipine were administered with either 150 ml of orange juice or 75 ml of alcohol (94%) in 75 ml of orange juice according to a crossover randomized design. Plasma nifedipine levels were monitored for 16 hr after each dosing, along with pulse rate and blood pressure. The relative bioavailability of nifedipine, measured as AUC, was increased by 54% (533 vs 346 ng.hr/ml) after the dose of alcohol (P less than 0.0002). However, there were no significant differences between treatments in Cmax, tmax, or t1/2. Although there was no difference in the systolic and diastolic blood pressure and pulse rate between the two treatment groups, the time to reach peak heart rate was significantly faster in the group treated with alcohol (1.4 vs 2.2 hr). This study shows that ethanol increases the bioavailability of nifedipine and decreases the time for onset of increased heart rate.

Pharmacodynamics as a tool to assess the bioequivalence of non-systemically available drugs: size of the sample required

Bioequivalence studies of drugs which are not systematically available must rely on the measure of the pharmacological response. Detection of a difference between two such preparations is often hampered by the need to include an elevated number of subjects. The number of subjects can be reduced whenever: (a) the characteristics of the subjects are well defined, (b) the selection of the baseline target effect is done rigorously, (c) the target effect can be quantified reliably, (d) the effect is measured when less variability is expected, e.g. at steady state, (e) the effect is measured repeatedly, and (f) when possible, the predicted maximal effect (Emax) and the concentration to elicit 50% of Emax are estimated. A simple equation has been derived to estimate the number of subjects needed in these bioequivalence studies.

Peripheral vasodilator and cardiac properties of the 1,5-benzothiazepine calcium antagonist analog, TA-3090, in dogs

Diltiazem, a 1,5-benzothiazepine, has demonstrated efficacy in the treatment of numerous cardiovascular diseases. TA-3090, a newly synthetized 1,5-benzothiazepine compound was studied in open-chest anesthetized dogs to characterize its hemodynamic properties, to compare it with diltiazem, and finally to correlate hemodynamic properties and plasma level concentrations. Anesthetized open-chest dogs were instrumented with electronic devices and fluid-filled catheters to monitor cardiac, coronary, and peripheral hemodynamic changes. A cumulative intravenous bolus administration of TA-3090 (n = 16) or diltiazem (n = 15) (15, 50, 200, and 400 micrograms/kg) was carried out, and blood samples were taken before and 5 min following each dose administration. Hemodynamic changes were followed for 30 min after each administration, at which time most hemodynamic parameters were back to baseline levels. The results indicate that both TA-3090 and diltiazem elicit slight peripheral and coronary vasodilator properties at low doses (15 and 50 micrograms/kg). With higher dosage, hemodynamic effects were maximal: coronary blood flow increased by 75%, arterial pressure decreased by 25%, and reflex positive inotropic effects were also observed. Heart rate was significantly reduced (10%). Comparison between TA-3090 and diltiazem indicates that both drugs elicit coronary vasodilator selectivity and TA-3090 has a prolonged duration of action compared with that of diltiazem. A straightforward relationship is demonstrated between vasodilator properties and plasma levels of either TA-3090 or diltiazem. Our data suggest that with plasma levels between 40 and 80 ng/mL, significant hemodynamic changes were observed with TA-3090. Changes of heart rate were not correlated with plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Diltiazem pharmacokinetics in elderly volunteers after single and multiple doses

In young healthy volunteers diltiazem does not have linear kinetics between single and multiple doses. Elimination half-life increases and gives AUC's and Cmax higher than those predicted from single dose data. Kinetics of diltiazem were assessed in 16 healthy elderly after a single 60 mg dose and in 24 healthy elderly after 60 mg every 8 h for 7 days. Thirteen participants completed both studies. Elimination half-life, AUC0-24, AUC0-infinity, and Cmax were (mean +/- SE) 7.4 (1.2) h, 349 (34) ng/ml.h, 392 (44) ng/ml.h, and 43 (5) ng/ml respectively after a single dose. After multiple doses elimination half-life, AUC0-48, AUC0-infinity, Cmax and Cmin were respectively 5.7 (0.3) h, 974 (107) ng/ml.h, 1022 (108) ng/ml.h, 102 (7) ng/ml and 43 (5) ng/ml. Exploratory statistics on the 13 volunteers common to both studies showed that the ratio of AUC desacetyl-diltiazem (DAD)/AUC diltiazem rose between single and multiple doses while elimination half-life of both diltiazem and N-desmethyl-diltiazem (MA), tmax, and AUC MA/AUC diltiazem were not affected. The conclusion of this study is that elimination half-life of diltiazem does not increase in elderly between single and multiple doses, possibly due to an increased biotransformation into DAD.

Pharmacokinetics of oral diltiazem and five of its metabolites in patients with chronic renal failure

The pharmacokinetics of oral diltiazem were studied in 10 patients with chronic renal failure not requiring dialysis and in five healthy volunteers after a single dose of 120 mg. We found that patients with chronic renal failure had lower amounts of unchanged diltiazem and of its main metabolite (MA) in urine and a trend to have slightly higher values of plasma concentration. Since the terminal elimination phase is not affected by chronic renal failure we conclude that this trend is probably the result of alterations in the volume of distribution of diltiazem in these patients.

Pharmacokinetics of intravenous diltiazem and five of its metabolites in patients with chronic renal failure and in healthy volunteers

The pharmacokinetics of diltiazem were studied in seven patients with chronic renal failure (CRF) not requiring dialysis and in three healthy volunteers after a rapid i.v. infusion of 20 mg. Mean plasma concentrations at the end of infusion were 3.15 times higher in patients with CRF than in healthy volunteers. From 0.5 to 12 h post-infusion, the difference remained between 25 per cent and 73 per cent. Mean AUC0-infinity was statistically greater in patients than in volunteers while mean V area, CLtot, and CLren were statistically lower. The t1/2 alpha and t1/2 beta values were not significantly (p greater than 0.05) different between patients and volunteers. Renal excretion was statistically more important in volunteers (6.6 per cent of the dose) than in patients (1.2 per cent of the dose). We therefore conclude that CRF does not influence t1/2 beta of diltiazem but it interferes with the extent and possibly the rate of its extravascular distribution. That could result in transient high plasma concentrations after rapid i.v. infusion.

Multiple-dose propranolol administration does not influence the single dose pharmacokinetics of quinapril and its active metabolite (quinaprilat)

To evaluate the influence of multiple dose propranolol administration on the single dose pharmacokinetics of quinapril and its active metabolite, quinaprilat, a drug-drug interaction study was performed in ten healthy volunteers. Each subject received a single 20 mg quinapril oral dose on Days 1 and 16 of the study. Oral propranolol doses of 40 mg BID were initiated on Day 3, titrated gradually to 80 mg TID by Day 10, and continued at 80 mg TID through Day 17. Comparable mean quinapril pharmacokinetic parameter values as well as comparable mean quinaprilat pharmacokinetic parameter values determined following quinapril administered alone and following quinapril administered with propranolol, indicate that propranolol does not alter the single dose pharmacokinetics of quinapril or quinaprilat.

Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules

The influence of food on the bioavailability of a conventional tablet and of a slow-release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 x 30 mg, first group) or as a slow-release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazem, and deacetyldiltiazem were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC infinity) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC infinity of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow-release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.

Pharmacokinetic interaction between flurbiprofen and antacids in healthy volunteers

Gastrointestinal distress resulting from drug intake is often remedied by administering the drug with antacids. However, antacids have been shown to modify the absorption and excretion of many drugs. This study was designed to delineate the effects of aluminium and magnesium hydroxide antacid suspension (Maalox) on the pharmacokinetics of flurbiprofen. Since this drug is often used in the elderly, not only young healthy but also geriatric healthy male volunteers participated in the study. A group of twelve young and a group of seven geriatric volunteers received, in a crossover design, a single oral dose of 100 mg of flurbiprofen with and without Maalox. A non-stereospecific assay was used to determine the total (R + S enantiomers) of flurbiprofen in plasma. The relative pharmacokinetic parameters of total flurbiprofen determined from plasma samples were Cmax, tmax, Kel, t1/2, and AUC infinity. The results indicate that the co-administration of Maalox with flurbiprofen had no effect on the rate and extent of total flurbiprofen absorption in young volunteers. In geriatric volunteers, the results indicate no effect of the antacid on the extent of drug absorption. There was a trend for lower plasma concentrations of total flurbiprofen with antacid in the geriatric group and hence a reduction in rate of flurbiprofen absorption although differences were not significant. The study also included a steady state determination of the influence of antacid administration on flurbiprofen pharmacokinetics. The group of young volunteers received, from Day 3 to Day 8, 100 mg of flurbiprofen every 12 h with and without Maalox.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of food and sucralfate on the pharmacokinetics of naproxen and ketoprofen in humans

Compliance to nonsteroidal anti-inflammatory drug therapy can be compromised by gastrointestinal side effects. To overcome this problem, food, antacid, or sucralfate are often co-administered with nonsteroidal anti-inflammatory drugs. Three studies were conducted on three groups of 12 volunteers in order to determine the influence of food or sucralfate on the pharmacokinetics of naproxen and ketoprofen. In a crossover experimental design, the first group received a single dose (50 mg) of ketoprofen with and without sucralfate (2 g). The second group received single (100 mg) and multiple (100 mg twice daily for 5 days) doses of enteric-coated ketoprofen with and without food. The third group received single (500 mg) and multiple (500 mg twice daily) doses of naproxen with and without sucralfate. Multiple blood samples were drawn and analyzed by high-pressure liquid chromatography. Short- and long-term pharmacokinetic parameters were determined. Results in group 1 showed that neither ketoprofen bioavailability nor maximal plasma concentration and time to reach maximal concentration were affected by the administration of sucralfate. However, in group 2 absorption of ketoprofen was markedly affected by food. In the presence of food, maximal plasma concentration decreased from 10.7 to 6.3 micrograms/ml after single-dose administration and 12.1 to 8.0 micrograms/ml after multiple-dose administration. The time to reach maximal plasma concentration was also modified by food, increasing from 2.8 to 7.1 hours after single-dose and 2.8 to 7.6 hours after multiple-dose administration. Food caused a significant decrease in the bioavailability of ketoprofen (over 40 percent) following both single-dose (23.8 versus 13.1 micrograms.hour/ml) and multiple-dose (29.3 versus 16.8 micrograms.hour/ml) administration. Results obtained in group 3 showed that sucralfate reduced the absorption rate constant of naproxen, from 1.7 to 1.2 hours-1 and from 1.5 to 0.7 hour-1 following single- and multiple-dose administration, respectively. However, bioavailability of naproxen was not affected by sucralfate administration. Overall, these studies have shown that sucralfate does not alter the pharmacokinetics of naproxen and ketoprofen; the amount of drug absorbed remains constant. However, plasma concentrations of ketoprofen after single- and multiple-dose administration were greatly affected by food, with a decrease of greater than 40 percent in bioavailability.

Determination of opiates and other basic drugs by high-performance liquid chromatography with electrochemical detection

A procedure is described for the extraction and determination of morphine (M), hydromorphone (HM), codeine (C) and metoclopramide (MCP) present in human plasma. The drugs are separated by reversed-phase liquid chromatography and detected amperometrically at a glassy carbon electrode. The method provides high sensitivity and selectivity and has been used successfully in bioavailability studies.

Placebo-controlled comparative study of the anxiolytic activity and of the pharmacokinetics of oral and sublingual lorazepam in generalized anxiety

In a randomized crossover study, twelve patients presenting a generalized anxiety disorder received either a 1 mg oral tablet or a 1 mg sublingual tablet of lorazepam three times daily for 7 days. After a 7-day washout period, each patient received a 7-day treatment with the other tablet form. Treatments were administered in a double-blind manner using placebos of both the oral and sublingual tablets. Psychiatric evaluations were carried out before and following each of the three periods. Blood samples were drawn at intervals for 48 h following the last dose of each treatment. The plasma concentrations of lorazepam were measured by gas chromatography using an electron-capture detector. Both the oral and sublingual lorazepam produced a significant anxiolytic effect; there was no statistically significant difference between the therapeutic effectiveness of the two forms of lorazepam. The main pharmacokinetic parameters for the oral and sublingual tablets were, respectively: elimination half-life 15.6h and 11.7h; maximal concentration 40.8 ng ml-1 and 42.2 ng ml-1; time to reach maximal concentration 1.2h and 1.4h; corrected area under the curve 310.6 ng hml-1 and 313.6 ng hml-1. There was no statistically significant difference between the oral and sublingual tablets for any of the pharmacokinetic parameters measured.

HPLC determination of indalpine and its major metabolite in human plasma and a pharmacokinetic application

A high-performance liquid chromatographic method using a fluorometric detector was developed for the determination of plasma concentrations of the antidepressant indalpine (I) and its major metabolite 4-[2-(3-indolyl)ethyl]-2-piperidinone (PK). the same procedure was used to measure, in urine, levels of I and of the metabolite, either conjugated or unconjugated. The sensitivity of the assay is 5 ng ml-1 of plasma or urine for both I and PK. Mean recoveries from plasma for PK, I, and the internal standard (quinine sulfate) were 86.4, 86.8, and 88.5 per cent, respectively. Mean recovery from urine for I was 82.5%. This method was used to establish the pharmacokinetic profiles of I and PK following a single oral administration of I (100 mg) in 8 healthy volunteers. Peak plasma concentrations for I and PK were obtained in an average time of 2.1 and 2.6 h (tmax), respectively. The mean absorption t1/2 of I was 0.8 h, the mean Vda 878 l and the mean clearance 58 l h-1. The mean t1/2 for I and PK was 10.4 and 11.9 h, respectively. In a 12 h urine collection 3 per cent of I was excreted unchanged. No conjugated or unconjugated metabolite was found in urine samples. This method was also used to determine plasma levels 10 h post-dose (50 mg t.i.d.) during chronic oral administration in 20 hospitalized patients. Mean plasma concentrations of I and PK post-dose were 116 ng ml-1 and 43 ng ml-1, respectively.

Chloroform interaction with chlordecone and mirex: correlation between biochemical and histological indices of toxicity and quantitative tissue levels

The purpose of this study was to investigate whether the tissue distribution of chlordecone (CD) and mirex (M) might explain the difference in the potentiation of CHCl3 liver injury. Male Sprague-Dawley rats received either a single oral dose of CD or M (1, 2.5, 5, 10, 25, or 50 mg/kg) or three single daily doses of CD or M (0.5, 2, or 10 mg/kg). Eighteen hours following the last treatment, the animals were divided into two groups. The first group was killed and residues of CD or M in plasma, kidney, liver, and adipose tissue were measured by gas-liquid chromatography. The other group received CHCl3 (0.5 ml/kg, po) and was killed 24 hr later. Biochemical and histological indices of liver injury were evaluated. CD administered either singly or repetitively is more effective than M in potentiating the CHCl3-induced liver injury. This was exhibited by a higher increase in the plasma activities of the enzymes alanine aminotransferase and ornithine carbamoyl transferase and a greater alteration of the morphological pattern. There was a very good correlation between biochemical and histological indices. However, the severity of the liver injury did not parallel tissue concentrations. With M, a relatively poor potentiation of the liver damage was observed although adequate hepatic concentrations were present.

Single dose pharmacokinetics of ketoprofen, indomethacin, and naproxen taken alone or with sucralfate

The effects of sucralfate on the rate and extent of absorption of ketoprofen, indomethacin, and naproxen were investigated in healthy volunteers. Six volunteers each received sucralfate (2 g) half an hour before a ketoprofen (50 mg) capsule, and, on another occasion, a ketoprofen (50 mg) capsule alone according to a 2 X 2 Latin square pattern of administration. The same design was used for studies with indomethacin (50 mg) capsules and naproxen (500 mg) tablets. Sucralfate decreased significantly (p less than 0.05) the maximum plasma concentrations (Cmax) of ketoprofen, indomethacin, and naproxen. Although the time necessary to attain Cmax (tmax) for the three drugs tended to increase, only for indomethacin was this increase significant. Sucralfate decreased significantly the rate of absorption (ka) of naproxen and indomethacin, but not that of ketoprofen; it had no significant effect on the elimination half-life and area under the plasma concentration as a function of time curves (AUC0----infinity) of the three drugs. Sucralfate thus decreases the Cmax and increases the tmax of ketoprofen, indomethacin, and naproxen without affecting their bioavailabilities.

The effect of administration of phenytoin on the pharmacokinetics of isoxicam

This study was designed to determine whether the disposition of isoxicam is influenced by the coadministration of another acidic drug, highly bound to plasma proteins and extensively metabolized, i.e., phenytoin. Ten healthy volunteers received an oral dose of 200 mg of isoxicam prior to and following the oral administration of phenytoin (100 mg) twice a day for 10 days. Eleven blood samples were drawn during the period following each dose of isoxicam. The area under the isoxicam plasma concentration-time curve (AUC infinity) increased from 389 +/- 66 to 464 +/- 62 micrograms h ml-1 (+/- SEM) (p less than 0.05) after treatment with phenytoin. This increase was due to an increase in isoxicam bioavailability; the absorption rate constant for isoxicam increased correspondingly from 0.34 +/- 0.06 to 1.16 +/- 0.38 h-1 (p less than 0.05). Distribution and clearance of isoxicam were probably not affected as its half-life was not changed, its plasma peak concentration increased, and the time to reach this peak decreased. It is concluded that phenytoin increases the rate and extent of absorption of isoxicam.

Temporal relationships between biotransformation, detoxication, and chlordecone potentiation of chloroform-induced hepatotoxicity

Exposure to chlordecone (CD, Kepone) is known to increase the hepatotoxicity of chloroform (CHCl3) in rats. A time-course analysis was conducted relating several indices of biotransformation capacity with the ability of CD to potentiate CHCl3-induced hepatotoxicity. Male Sprague-Dawley rats were given a single administration of corn oil alone or CD (50 mg/kg, po) dissolved in corn oil. At 2, 4, 8, 16, 20, 24, or 32 days posttreatment, groups of rats were killed and their livers were analyzed for (i) cytochrome P-450, NADPH-dependent cytochrome c reductase, cytochrome b5 and glutathione content or (ii) in vitro irreversible binding of 14CHCl3-derived radiolabel to microsomal protein. Similarly treated rats were challenged (2-32 days posttreatment) with CHCl3 (0.5 mL/kg po); 24 h later, liver damage was assessed by plasma alanine aminotransferase (ALT), plasma ornithine carbamyl transferase (OCT), plasma bilirubin, and hepatic glucose-6-phosphatase. CD potentiation was maximal 2 days posttreatment; and enhanced susceptibility to CHCl3 persisted up to 20-24 days post-CD treatment. In a parallel study animals treated with chlordecone were killed 8, 16, 20, 24, or 32 days later. Blood, kidney, liver, and adipose tissue samples were taken and analyzed for chlordecone content. The results suggest that a general temporal correlation exists between biotransformation rate (microsomal 14C binding), chlordecone content, and the severity of liver injury; the other parameters monitored do not appear to relate directly to the potentiation.

The effect of administration of propranolol on the pharmacokinetics of isoxicam

In order to examine a potential interaction between isoxicam and propranolol, single 200 mg doses of isoxicam were administered to ten healthy male volunteers before and during treatment with propranolol, gradually attaining a dose of 80 mg t.i.d. for 11 days. The pharmacokinetic profiles of the isoxicam plasma concentration/time data obtained over 96 h following the doses of isoxicam before and during propranolol administration were compared. No significant change was found in any of the pharmacokinetic parameters determined. These results suggest that propranolol has no effect on the metabolic disposition of isoxicam.

Novel assay and pharmacokinetics of levamisole and p-hydroxylevamisole in human plasma and urine

A new gas chromatographic method was developed for the quantification of levamisole in human plasma and urine, using a nitrogen-phosphorus flame ionization detector. The adsorption of the drug onto glass was prevented by treating the glassware with a siliconizing agent. The sensitivity of the assay was 10 ng ml-1 and as low as 2 ng ml-1 can be detected in plasma. The urinary metabolite p-hydroxylevamisole was analysed by high performance liquid chromatography with ultraviolet detection. The sensitivity of this assay was 0.50 micrograms ml-1. Plasma and urinary concentrations of levamisole were determined in 10 healthy volunteers including seven men and three women following the administration of a single 150 mg dose of levamisole. Levamisole was rapidly absorbed (tmax 1.5 h), giving a peak plasma concentration of 716.7 +/- 217.5 ng ml-1. The plasma elimination half-life of levamisole was 5.6 +/- 2.5 h. Only 3.2 +/- 2.9 per cent of the oral dose was recovered as unchanged drug in the urine, suggesting the importance of clearance of levamisole by routes other than the kidney, and most probably by hepatic metabolism. The urinary concentrations of p-hydroxylevamisole were determined before and after hydrolysis of the urine samples with beta-glucuronidase, and the level of conjugation of the metabolite with glucuronic acid was then estimated. Cumulative recovery of the metabolite accounted for 1.6 +/- 1.1 per cent and 12.4 +/- 5.5 per cent of the oral dose of levamisole before and after hydrolysis, respectively, indicating that p-hydroxylation is a relatively important route of metabolism of levamisole, and that the p-hydroxylated metabolite is excreted mainly in conjugation with glucuronic acid. Except for the absorption rate of levamisole which is approximately twice as rapid in women as in men, there is no marked difference in the pharmacokinetics of levamisole between healthy men and women.