Metabolism of the platelet-activating factor antagonist (+/-)-trans-2-(3'-methoxy-5'-methylsulphonyl-4'-propoxyphenyl)-5-(3",4" ,5"- trimethoxyphenyl)tetrahydrofuran (L-659,989) in rhesus monkeys.

1. The plasma concentration, main route of metabolism and excretion of 3H-L-659,989 were studied in male and female rhesus monkeys by dosing either i.v. or orally at 10 mg/kg. 2. The percentage of the AUC for the plasma radioactivity concentration-time curve of oral vs i.v. dosed monkeys was 78% for males and 90% for females, indicating that the dose was well absorbed. 3. The bioavailability of the drug was low (less than or equal to 10%) for all monkeys, probably due to rapid first pass metabolism. The drug was metabolized-predominantly at the C-4'-propoxy side-chain. The two major plasma metabolites were identified as the 4'-2-(hydroxy)propoxy metabolite (3H-trans-4'-HP) and the 4'-hydroxy metabolite (3H-4'-hydroxy) which was isolated as a 2:1 mixture of (+/-)trans: (+/-)cis. 4. Approx. 80% of the radiolabelled dose was excreted equally in the urine and faeces in 96 h, with the largest percentage of the tritiated dose (31 +/- 4%) in the 0-24 h urine. 5. The major metabolites in the excreta were the (+/-)trans/(+/-)cis mixture of 3H-4'-hydroxy and the glucuronide conjugate of 3H-trans-4'-hydroxy. The glucuronide conjugate of 3H-trans-4'-hydroxy was excreted in the urine of i.v. and orally dosed monkeys and represented an average of 21% and 5.1% of the dose, respectively. 3H-4'-Hydroxy was excreted in both the urine and faeces, accounting for less than or equal to 0.1% and 7.4% of the dose in i.v. and orally dosed monkeys, respectively.

Metabolism of kadsurenone and 9,10-dihydrokadsurenone in rhesus monkeys and rat liver microsomes.

The metabolism of the PAF antagonists kadsurenone and tritium-labeled 9,10-dihydrokadsurenone was studied in rhesus monkeys and rat liver microsomes. The monkey metabolites of the two drugs were isolated as their glucuronide conjugates from the urine of iv dosed males. The metabolites from both monkey and microsomal metabolism were purified by reverse phase HPLC and identified by spectral (NMR, UV, and mass spectrometric) analysis. The principal pathway of biotransformation of the tritium-labeled 9,10-dihydrokadsurenone in monkeys was hydroxylation of the C-5 propyl side chain to give two metabolites, 10-hydroxy-9,10-dihydrokadsurenone and 9-hydroxy-9,10-dihydrokadsurenone. These compounds were excreted as glucuronides. Microsomal incubation of tritium-labeled 9,10-dihydrokadsurenone yielded the 10-, 9-, and 8-hydroxy-9,10-dihydrokadsurenone as major metabolites. Kadsurenone was also metabolized at the C-5 side chain, an allyl group. The monoglucuronide of 9,10-dihydroxykadsurenone was isolated from monkey urine. Spectral analysis was not definitive as to the site of conjugation, and the structure of the metabolite was assigned as the C-10 conjugate. A major metabolite of rat liver microsomal incubation of kadsurenone was 9,10-dihydroxykadsurenone.

A peripherally acting alpha-2 adrenoceptor antagonist: L-659,066.

L-659,066 has been characterized as a potent and selective alpha-2 adrenoceptor antagonist. Both in vitro and in vivo, L-659,066 exhibited specificity (comparable to rauwolscine) for alpha-2 over alpha-1 adrenoceptors. Studies comparing L-659,066 with a previously described antagonist, L-657,743, demonstrate that the new compound penetrates the blood-brain barrier only poorly after systemic administration. With a pA2 of 8.44 at alpha-2 adrenoceptors in the isolated rat vas deferens and an IC50 of 3.0 nM against the binding of [3H]rauwolscine to rat cerebrocortical membranes, L-659,066 possessed, respectively, about one-eighth and one-third of the potency of L-657,743. Similar relative potencies were obtained in vivo in pithed rats with regard to blocking peripherally located postjunctional and prejunctional alpha-2 adrenoceptors (L-659,066 = one-seventh and one-fourth of L-657,743, respectively). In tests carried out in vivo with rats for ascertaining alpha-2 adrenoceptor antagonism in the central nervous system--namely, accumulation of cortical dopa and antagonism of mydriasis induced by the alpha-2 agonist, clonidine--L-659,066 had, respectively, less than 1/345th and about 1/5000th of the potency of L-657,743. In mice, L-659,066 had, respectively, approximately 1/29th and 1/1400th of the potency of L-657,743 as an antagonist in vivo of the predominately peripherally mediated inhibition of colonic propulsion caused by clonidine as compared with the mainly centrally mediated antinocisponsive action elicited by the alpha-2 agonist UK 14,304. The foregoing findings are consistent with poor penetration of the blood-brain barrier by L-659,066.(ABSTRACT TRUNCATED AT 250 WORDS)

Single-dose pharmacokinetics and bioavailability of famotidine in man. Results of multicenter collaborative studies.

Pharmacokinetics and bioavailability of famotidine, a new H2-receptor antagonist, were investigated in healthy subjects in five clinical studies. Linear pharmacokinetics were observed following either intravenous or oral administration. Plasma clearance averaged 463 ml min-1. Renal clearance averaged 310 ml min-1, which exceeded the glomerular filtration rate. Renal excretion was the major route of elimination. Urinary recovery of unchanged drug following intravenous administration was about 67 per cent. Famotidine plasma half-life was approximately 2.6 h. Oral absorption was incomplete. The bioavailability averaged 43 per cent of the dose.

Determination of cyproheptadine in plasma and urine by GLC with a nitrogen-sensitive detector.

A method for the determination of cyproheptadine in plasma and urine was developed using the N -ethyl homologue as an internal standard. After extraction of the drug from an alkalinized sample into petroleum ether-isoamyl alcohol, back-extraction into 0.1 N HCl, washing the aqueous phase with fresh solvent, re-extraction into petroleum ether after alkalinization, the solvent was evaporated. The reconstituted residue was analyzed by GLC using a SP-2250 column and nitrogen-sensitive detector. Concentrations as low as 3 ng/ml could be determined. Plots of peak area of cyproheptadine-peak area of internal standard versus cyproheptadine concentration were linear over the range studied with correlation coefficients of 0.9945 and 0.9924 for plasma and urine, respectively. The method was used to determine the peak time (0.5 hr), peak concentration (33 ng/ml average), and apparent half-life (3 hr) in two dogs after oral administration of 1 mg of cyproheptadine/kg.

GLC determination of (-)-1-cyclopropylmethyl-4-(3-trifluoromethylthio-5H-dibenzo [a,d]cyclohepten-5-ylidene)piperidine in human plasma and urine.

(-)-1-Cyclopropylmethyl-4-(3-trifluoromethylthio-5H-dibenzo [a,d]cyclohepten-5-ylidene)piperidine (MK-160) was extracted from human plasma and urine with petroleum ether and quantitated by GLC using a nitrogen-sensitive detector. A homologue of the drug served as the internal standard. The method is specific for the drug in the presence of potential metabolites and is capable of measuring concentrations in plasma as low as 6 ng/ml.

Disposition and metabolism of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine in rats, dogs, and monkeys.

The disposition and metabolism of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), a new agent with potent anticonvulsant, central sympathomimetic, and apparent anxiolytic properties, was studied in rats, dogs, and rhesus monkeys. [3H]benzene-MK-801 was administered orally at a dose of 1 mg/kg. MK-801 was measured in plasma by GLC using a nitrogen detector; the overall sensitivity of the method was 3 ng/ml. Radioactivity was excreted mainly in urine of dogs and monkeys but fecal excretion in rats was also extensive. The apparent plasma t1/2 of MK-801 in the rat and dog was approximately 1 hr. Maximal plasma levels of MK-801 in the rat, dog, and monkey were 46 (0.5 hr), 16 (0.25 hr), and 10 (2 hr) ng/ml, respectively. Radioactivity was extensively excreted in rat bile and was widely distributed among various tissues. Major metabolites of the drug in rat and dog urine were the 2- and 8-hydroxy analogs (rat) and the N-hydroxy derivative (dog).

Physiologic disposition and metabolism of an anti-ulcer agent, N-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)-N',N'-dimethylurea, in rats, dogs, and monkeys.

14C-N-(2-Diisopropylaminoethyl)-N-(4,6-dimethyl-2-dimethyl- 2-pyridyl)-N',N'-dimethylurea (I) was administered orally to dogs and rats and to rhesus, African green, and squirrel monkeys. Radioactivity was excreted mainly in the urine (60-76%) of all species except the rat (25%). The plasma t1/2 of I in the dog was 0.8 hr. Five urinary metabolites were identified by TLC, GLC, GS/MS, and NMR spectrometry: N,N-dimethyl-N'-(2-diisopropylaminoethyl)-N'-(4-hydroxy-methyl-6-methyl-2-pyridyl)urea (II), N,N-dimethyl-N'-(2-diisopropylaminoethyl-N'-(4-methyl-6-hydroxymethyl-2-pyridyl )urea (III), N,N-dimethyl-N'-(2-isopropylaminoethyl)-N'-(4,6-dimethyl-2-pyridyl)urea (IV), N-methyl-N'-(2-diisopropylaminoethyl)-N'-(4,6-dimethyl-2-pyridyl)urea (V), and N-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)urea (VI). II was a major urinary metabolite in dog and II and IV were major metabolites in the squirrel monkey. II was present in relatively high concentrations in testes and stomach tissues of dogs, but not rats, treated with I, a finding that may be related to species differences in toxicity observed with I in these species.

Metabolism of protriptyline by rabbit liver in vitro.

A new metabolite of protriptyline formed by incubation of the drug in a rabbit liver microsomal system was identified as the hydroxylamine derivative by mass spectral and NMR analysis.

Physiological disposition and metabolism of cyclobenzaprine in the rat, dog, rhesus monkey, and man.

The absorption, distribution, excretion, and metabolism of 3-(5 H-dibenzo[a,d]cyclohepten-5-ylidene)-N,N-dimethyl-1-propanamine (cyclobenzaprine) were investigated in the rat, dog, rhesus monkey, and man. The drug was well absorbed in all species after oral administration. The rat eliminated the drug primarily in the feces, but urinary excretion was predominant in the dog, monkey, and man. The drug was rapidly and widely distributed into rat tissues, highest concentrations being found in the small intestine, lung, kidney, and liver. The drug was highly bound in human plasma. Extensive biliary excretion of the labeled compound was observed in the rat. Major metabolites in the rat were phenolic derivatives but in man the major metabolites were 10,11-dihydroxynortriptyline and cyclobenzaprine glucuronide. Only minor amounts of unchanged drug were present in the urine.

Metabolism of cyclobenzaprine in the dog.

Ten metabolites of cyclobenzaprine, accounting for approximately 50% of the urinary radioactivity, were identified in the urine of dogs to which the labeled drug had been given orally. These included the 1,2-dihydrodiol, three phenolic derivatives, the N-oxide, the 10,11-epoxide, the 10,11-glycol, desmethylcyclobenzaprine, and the glucuronide conjugates of desmethylcyclobenzaprine and cyclobenzaprine. The metabolites were excreted in both the free and conjugated states. Unchanged cyclobenzaprine was present in only minor amounts.

Plasma levels and bioavailability of cyclobenzaprine in human subjects.

Cyclobenzaprine was extensively metabolized in man, less than 1% of the dose being excreted unchanged in the urine. Comparison of areas under plasma level curves (AUC) after oral and intravenous doses suggests that the drug may be partly metabolized in the lumen or during its first passage through the gut wall and/or liver. Average plasma levels of the drug increased with increasing dosage, but the AUC increased less rapidly with increasing dose, possibly because of dose-dependent absorption.

Rapid, sensitive gas-liquid chromatographic method for determination of amitryptyline and nortriptyline in plasma using a nitrogen-sensitive detector.

A simple gas chromatographic method for determination of amitriptyline and nortriptyline in plasma using a nitrogen-sensitive detector is described. Concentrations of both drugs as low as 10 ng per ml plasma were measured. The precision and accuracy of the method are within acceptable limits.

Urinary metabolites of amitriptyline in the dog.

Dogs excreted approximately 45% of an oral dose of 14C-amitriptyline (30 mg/kg) in the urine in 24 hr. Two new urinary metabolites of the drug were identified as dihydrodiol derivatives of amitriptyline and nortriptyline, respectively. The major metabolite in dog urine was 10-hydroxyamitriptyline, excreted mainly in conjugated form. Other metabolites were characterized as 10-hydroxynortriptyline, amitriptyline N-oxide, and nortriptyline. Together, these metabolites accounted for approximately 47% of the urinary radioactivity.

Determination of various drugs in rodent diet mixtures.

Methods employing solvent extraction, thin-layer chromatography, gas-liquid chromatography, and UV spectrophotometry are described for the quantitative determination of halofenate, cyclobenzaprine and sulindac in rodent diet mixtures. Halofenate was hydrolyzed to its free acid derivative and converted to a methyl ester prior to assay. The drugs were shown to be stable when stored in food mixtures at room temperature for seven days. Diet mixtures containing the three drugs were demonstrated to be uniformly mixed by the procedure employed.

Bioavailability assessment under quasi- and nonsteady-state conditions III: Application.

The applicability of bioavailability assessment at quasi- and nonsteady state is illustrated with data from a study comparing two formulations of amitriptyline hydrochloride in humans. Relative bioavailability as a function of the observed mean plasma concentrations may be expressed in closed form, provided the affected intervals begin and end in the log-linear region. Alternatively, numerical, graphical and/or electronic computational techniques may be used to stimulate the appropriate [Cp(i)]sim, the proximity of which to [Cp(i)]obs is a function of relative bioavailability and omega. If a model can be found to fit the data adequately, it would be sufficient that only one sampled interval end in the log-linear phase.

GLC determination of cyclobenzaprine in plasma and urine.

A GLC determination of cyclobenzaprine in human plasma and urine is described. After extraction from alkalinized samples with heptane-isopentyl alcohol (97:3), the drug and internal standard were back-extracted into 0.1 N HCl and then reextracted into ether. Use of a lower homolog of the drug as an internal standard was effective in reducing variability. Drug concentrations as low as 25 ng/ml could be assayed with high precision. Plasma levels in humans given 40 mg po or iv ranged from 5 to 51 ng/ml; little unchanged cyclobenzaprine was present in the urine. The N-desmethyl analog of the drug was detected as a metabolite in urine.