Toxicokinetics of 2',3'-didehydro-3'-deoxythymidine, stavudine (D4T).

The toxicokinetic profile of D4T was assessed by conducting in vivo and in vitro studies. In the various studies, the i.v. and oral doses ranged from 12.5 to 600 and 5 to 2000 mg/kg, respectively. D4T was rapidly absorbed with an absolute oral bioavailability ranging from 77 to 100% in various species. The steady-state volume of distribution of D4T ranged from 0.50 to 1.12 liters/kg; radioactivity was distributed in all tissues, with the highest concentrations in the organs of excretion, liver and kidneys. D4T was eliminated from the body with a half-life of 0.30 to 1.23 h. Urinary recovery of unchanged drug was species-dependent and ranged from approximately 37 to 86%. In the mass balance studies, the recovery of total radioactivity at 96 h in rats and monkeys was approximately 85% and 50%, respectively; fecal recovery was <1.5% and approximately 14% was recovered as 14CO2 in expired air in rats. The in vitro protein binding of D4T was negligible (<10%) and D4T did not induce cytochrome P-450 in rats or monkeys. D4T was metabolized to thymine and polar metabolites by the S9 and liver slices in vitro. Significant interspecies correlations were found for total body clearance, steady state of volume of distribution, and T1/2 and species body weight. The multiples of exposure observed at the various no-effect doses in the drug safety evaluation studies (10x - 1102x) affirm that adequate doses of D4T were administered to laboratory animals to discern potential human risk.

Pharmacokinetics of sematilide in renal failure.

A randomized, two-period, two-treatment study was conducted to investigate the effect of renal impairment on the pharmacokinetics of the Class III antiarrhythmic sematilide HCl. The pharmacokinetic-pharmacologic effect relationship and tolerability of sematilide HCl were also studied. The study included 22 subjects: 6 healthy volunteers and 16 patients with various degrees of renal impairment, including functionally anephric patients on intermittent hemodialysis. Separated by a 14-day washout period, the subjects received a constant rate intravenous infusion of 40 mg sematilide HCl over 30 minutes and a tablet containing 100 mg of the drug. The functionally anephric patients were studied during and off dialysis after intravenous and oral administration of the drug, respectively. Blood and urine samples were collected at defined times up to 48 hours and 72 hours, respectively, after administration. Sematilide concentrations in plasma, urine, and dialysate were measured by a validated high-performance liquid chromatography (HPLC) method with ultraviolet detection. The pharmacokinetic data analysis used a compartment model independent approach. The heart rate-corrected Lead II QT interval was recorded as a pharmacologic endpoint. Subjective symptoms, cardiovascular parameters, routine serum chemistry, and hematology and urinalysis parameters were measured to assess tolerability. Mean renal clearance after intravenous and oral administration was reduced in patients with severe renal impairment. Statistically significant linear correlations existed between total clearance of sematilide and creatinine clearance for all subjects who could be evaluated after both intravenous and oral administration. Steady-state volume of distribution, absolute bioavailability, and nonrenal clearance of sematilide were independent of renal function. The mean dialysis clearance was 98 mL/min, indicating effective removal of the drug by hemodialysis. In accord with the drug's Class III pharmacologic activity, the heart rate corrected Lead II QT intervals were prolonged in all subjects after intravenous and oral administration of the drug. The pharmacologic effect to plasma concentration relationship in renal patients and in healthy subjects was comparable. Based on the experimentally determined linear relationship between total clearance of sematilide and creatinine clearance, modified dose regimens for sematilide HCl in patients with renal impairment and functionally anephric patients off hemodialysis were developed.

Pharmacokinetics, absolute bioavailability, and disposition of [14C]nefazodone in humans.

The pharmacokinetics and disposition of nefazodone (NEF) were investigated after administration of intravenous (iv) and oral (po) doses to nine healthy men. All volunteers were administered a 5-mg dose of [14C]NEF by iv infusion on study day 1, and groups of three volunteers each were administered oral solution doses of 50, 100, and 200 mg of [14C]NEF, respectively, on study day 8. Total radioactivity in plasma, urine, and feces collected for 7 days after iv and po dosing was determined. Serial blood samples for pharmacokinetic analysis were also collected over a 48-hr period after iv and po administrations, and plasma samples were assayed for NEF, and the NEF metabolites hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP) by a specific, validated HPLC method. Over the po dose range of 50-200 mg, NEF was rapidly absorbed (tmax values for NEF, HO-NEF and total radioactivity were approximately 0.5 hr). Recovery of total radioactivity in the urine (approximately 50% of dose) was similar after iv and po administrations. Fecal excretion of radioactivity after iv administration of [14C]NEF suggested that biliary excretion also plays a role in drug elimination. The mean (SD) apparent absolute oral bioavailability of NEF was 15(7)%, 18(7)%, and 23(7)% at doses of 50, 100, and 200 mg, respectively. The apparent extent of presystemic metabolism over this dosage range was estimated to be 74-87%. In summary, after po administration, NEF was rapidly and completely absorbed, and extensively metabolized before elimination via urinary and fecal routes.

Pharmacokinetics of the anti-human immunodeficiency virus nucleoside analog stavudine in cynomolgus monkeys.

Stavudine was administered (15 mg/kg of body weight) intravenously and orally to two monkeys in a randomized crossover study. Plasma and urine samples were analyzed for stavudine by high-performance liquid chromatography, and pharmacokinetic parameters were derived by a noncompartmental method. Total body clearance of stavudine was 0.64 liters/h/kg, with a steady-state volume of distribution of 0.68 liters/kg, a terminal half-life of 0.83 h, a urinary recovery of 44%, and an oral bioavailability of 80%. These values were reasonably similar to those reported for patients with AIDS or AIDS-related complex.

Absorption, disposition, and metabolism of [14C]didanosine in the beagle dog.

The absorption, disposition, and metabolism of didanosine were investigated in three adult male beagle dogs that received a single iv and po solution dose of 200 mg (ca. 20 mg/kg) of [14C]didanosine. The dog model was "humanized" by predosing with pentagastrin (6 micrograms/kg). The po dose was in buffer, as administered in man. The iv and po sessions were separated by 1 week. Plasma, urine, and feces were collected and assayed for total radioactivity; plasma and urine samples were also analyzed for intact didanosine using validated HPLC/UV assays. Metabolic profiles of [14C]didanosine were obtained in plasma and urine. After iv dose, 87% and 0.5% of the administered radioactivity were recovered in urine and feces within 6 days, respectively; the corresponding recoveries were 84% and 2.1% after po dose. Oral absorption of didanosine was rapid and complete; but due to first pass metabolism, the absolute bioavailability of didanosine was 44%. Mean renal clearance of didanosine (110 ml/min) accounted for about 43% of the total body clearance. The mean steady state volume of distribution of didanosine was 9.6 liters. The mean terminal half-life of didanosine was 0.8 hr after iv or po administration. Five putative metabolites, M1 (allantoin), M2, M3 (uric acid), M4 (hypoxanthine), and M5 (xanthine) of didanosine were observed in plasma and/or urine. The sum of the five metabolites plus unchanged drug accounted for virtually all of the radioactivity in plasma and urine. Allantoin represented the major metabolite in both plasma and urine. The extent of metabolism and the proportion of dose excreted as unchanged didanosine were markedly route dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

The disposition and protein binding of batanopride and its metabolites in subjects with renal impairment.

We have studied the disposition of batanopride and its three major metabolites (the erythro-alcohol, threo-alcohol, and N-desethyl metabolites) in 27 subjects with various degrees of renal function after intravenous infusion of a single dose of 3.6.mg.kg-1 of batanopride over 15 min. The subjects were assigned to one of three treatment groups: group 1, normal renal function (creatinine clearance > or = 75 ml.min-1 x 1.73 m-2; n = 13); group 2, moderate renal impairment (creatine clearance 30-60 ml.min-1 x 1.73 m-2; n = 8); group 3, severe renal impairment (creatinine clearance < or = 30 ml.min-1 x 1.73 m-2; n = 6). The terminal half-life of batanopride was significantly prolonged from 2.7 h in group 1 to 9.9 h in group 3. The renal clearance of batanopride was significantly lower in group 3 (25 ml.min-1) compared with group 1 (132 ml.min-1). There were no differences in plasma protein binding or steady-state volume of distribution of batanopride among the groups. There were significantly lower renal clearances for all three metabolites in groups 2 and 3 compared with group 1. The half-lives of all three metabolites were significantly prolonged in group 3 compared with group 1. The dose of batanopride may need to be reduced in patients with creatinine clearances less than 30 ml.min-1 x 1.73 m-2 to prevent drug accumulation and avoid possible dose-related adverse effects.

High-performance liquid chromatographic determination of 2',3'-didehydro-3'-deoxythymidine, a new anti-human immunodeficiency virus agent, in human plasma and urine.

Sensitive and selective high-performance liquid chromatographic techniques have been developed for the determination of 2'-3'-didehydro-3'-deoxythymidine, d4T (BMY-27857), in human plasma and urine. The methods had linear standard curves over the concentration ranges 0.025-25.0 and 0.5-100 micrograms/ml for the plasma and urine matrices, respectively. Both methods used solid-phase extraction for isolating d4T and the internal standard, thymidine oxetane, from the biological matrix. In addition, the analytical column, mobile phase, instrumentation and chromatographic conditions used for both methods were identical. The ultraviolet absorbance of the column effluent was monitored at 266 nm. Results of analysis of quality control samples indicated that the intra-assay precision values, as measured by percent relative standard deviation, were within 12 and 3%, and accuracy samples deviated less than 10 and 5% from nominal values for the plasma and urine assays, respectively.

High-performance liquid chromatographic assay of alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMY 14802), a potential antipsychotic drug, in monkey and rat plasma.

A high-performance liquid chromatographic-fluorescence method was developed for the quantitative analysis of BMY-14802 (I) in monkey and rat plasma. After the addition of the internal standard (BMY-14853 I.S.), 250 microliters of plasma were made basic by the addition of 2 ml of saturated sodium carbonate buffer. Compound I and the I.S. were then extracted into 5 ml of methyl tert.-butyl ether. The organic phase was evaporated and the resulting residue was reconstituted in mobile phase. Final separation and quantitation of I was achieved on an octadecyl column with a 0.05 M potassium phosphate-acetonitrile-triethylamine-85% phosphoric acid (650:350:0.1:0.05, v/v) mobile phase. Fluorescence detection was used to monitor the eluent at an excitation wavelength of 240 nm and an emission wavelength of 400 nm. The limit of detection was 0.5 ng/ml. The standard curve was linear over the range 5.0-1000 ng/ml. Intra-assay and inter-assay precision values were less than 4.0% relative standard deviation and accuracy was within 12% of nominal values. Compound I was shown to be stable in monkey and rat plasma for at least six months when stored at -20 degrees C.

Pharmacokinetics of 2',3'-dideoxyinosine (BMY-40900), a new anti-human immunodeficiency virus agent, after administration of single intravenous doses to beagle dogs.

The pharmacokinetics of 2',3'-dideoxyinosine (ddI) were investigated in four adult male beagle dogs that received 15-min infusions of 20-, 50-, and 100-mg/kg doses in a randomized crossover study design. Plasma and urine samples were collected for 10 and 24 h, respectively, and assayed for ddI by high-performance liquid chromatographic methods. The mean maximum concentrations of drug in plasma at the end of 15-min infusions for the 20-, 50-, and 100-mg/kg doses were 33.3, 90.0, and 202 micrograms/ml, respectively. Area under the concentration-time curve data deviated significantly from linearity. The mean total clearance for the low dose (250 ml/min) was significantly greater than that for the high dose (190 ml/min). Renal clearance, which averaged between 98 and 116 ml/min, was dose independent. Renal clearance implied that nonrenal clearance decreased at the high dose (92 ml/min) when compared with that of the low dose (134 ml/min). The average urinary recovery of ddI for the high dose (51.2% of dose) was significantly greater than that for the low dose (45.8%). The volume of distribution at steady state averaged between 7.6 and 10.5 liters and decreased with increasing dose; however, it was not statistically significant. The mean half-life and mean residence time were invariant with respect to dose and averaged between 0.94 and 1.07 h and 0.61 and 0.71 h, respectively. In this dose range, ddI pharmacokinetics are dose dependent.

Determination of belfosdil, a new calcium channel blocker, in human plasma by capillary gas chromatography with nitrogen-phosphorus detection.

Belfosdil and the internal standard were extracted from human plasma by a double liquid-liquid extraction. After a concentration step, gas chromatographic analysis of the sample was performed using a capillary fused-silica column and a nitrogen-phosphorus detector. The limit of detection of belfosdil was 0.025 ng/ml and the standard curve was linear over the range 0.05-100 ng/ml. The intra-assay and inter-assay precisions were within 7% (relative standard deviation) and the intra-assay and inter-assay accuracy values deviated by less than 5%. The extractability of belfosdil was 79%. The assay method was successfully used for the analysis of plasma samples from clinical studies with dose ranges of 5-100 mg of belfosdil.

Liquid chromatographic determination of 9-methyl-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one in human plasma with fluorescence detection.

A simple and sensitive assay for quantitating 9-methyl-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one (1; BMY 26517) in human plasma was developed using high-performance liquid chromatography with fluorescence detection. The method involves precipitation of protein and reversed-phase chromatography. The method is linear in the range of 4.3-429 ng/mL of 1, and the limit of detection is 0.4 ng/mL. The day-to-day precision values of this method at 25.7 and 386 ng/mL are 2.1 and 2.6%, respectively. The day-to-day accuracy values at these concentrations are 99.7 and 99.8%, respectively. The recovery of 1 is 98.3%.

Clinical pharmacology of etintidine in patients with duodenal ulcer.

The gastric antisecretory activity of etintidine, a new histamine H2-receptor antagonist, was evaluated in 5 patients with quiescent duodenal ulcer disease. Meal-stimulated acid secretion was measured after 100 and 300 mg oral doses of etintidine, 100 and 300 mg oral doses of cimetidine, and placebo. Reductions from placebo in four-hour gastric acid secretion were 49, 65, 80, and 94%, with 100 mg cimetidine, 100 mg etintidine, 300 mg cimetidine, and 300 mg etintidine, respectively. Drug concentrations in plasma were determined by HPLC. The pharmacokinetics of the 2 drugs were similar. We analyzed sigmoid-shaped concentration-response curves to both agents; the concentrations causing 50% inhibition of meal-stimulated gastric acid secretion were 0.44 +/- 0.04 and 0.15 +/- 0.04 micrograms/ml for cimetidine and etintidine, respectively. However, characteristics of these curves were such that the potency difference diminished at higher concentrations.

Effect of sodium salicylate on renal elimination of a quaternary ammonium compound.

Administration of sodium salicylate inhibited elimination of the tetraethylammonium ion in rats. A two-compartment open model was used to describe plasma decline of tetraethylammonium bromide administered intravenously. The rate constant describing elimination from the central compartment was decreased by 25 and 40% in rats predosed with sodium salicylate at 30 and 50 mg/kg, respectively. Salicylate also enhanced the distribution of the tetraethylammonium ion to the peripheral compartment. Urinary excretion is the principal route of elimination for the tetraethylammonium ion, and studies of the effect of sodium salicylate on the uptake of the tetraethylammonium ion by rat renal cortical tissue indicated noncompetitive inhibition by salicylate.