Species differences in the pharmacokinetics and metabolism of reparixin in rat and dog.

The pharmacokinetics and metabolism of reparixin (formerly repertaxin), a potent and specific inhibitor of the chemokine CXCL8, were investigated in rats and dogs after intravenous administration of [14C]-reparixin L-lysine salt. Protein binding of reparixin was investigated in vitro in rat, dog, rabbit, cynomolgus monkey and human plasma. Plasma protein binding of reparixin was >99% in the laboratory animals and humans up to 50 microg ml-1, but lower at higher concentrations. Although radioactivity was rapidly distributed into rat tissues, Vss was low (about 0.15 l kg-1) in both rat and dog. Nevertheless, reparixin was more rapidly eliminated in rats (t1/2 approximately 0.5 h) than in dogs (t1/2 approximately 10 h). Systemic exposure in dog was due primarily to parent drug, but metabolites played a more prominent role in rat. Oxidation of the isobutyl side-chain was the major metabolic pathway in rat, whereas hydrolysis of the amide bond predominated in dog. Urinary excretion, which accounted for 80-82% of the radioactive dose, was the major route of elimination in both species, and biotransformation of reparixin was complete before excretion.

Metabolic fate of 14C-camostat mesylate in man, rat and dog after intravenous administration.

1. The metabolic fate of N,N-dimethylcarbamoylmethyl 4-(4-guanidino[14C]benzoyloxy)phenylacetate methanesulphonate (14C-camostat mesylate) was investigated after i.v. administration to man (12-h infusion), and to rat and dog (bolus injection). 2. Renal excretion (mainly in 24 h) accounted for at least 80% dose in all three species, and the only two important metabolites were identified as 4-(4-guanidinobenzoyloxy)phenylacetic acid (GBPA) and 4-guanidinobenzoic acid (GBA). 3. Parent drug was not detected in human plasma either during or after infusion of 14C-camostat mesylate owing to rapid hydrolysis of the side-chain ester group (t1/2 < 1 min). Steady-state levels of both GBPA and GBA in plasma were apparently attained by the end of the infusion period. Mean terminal half-life, systemic clearance and apparent volume of distribution at steady-state of GBPA in man were 1.0 h, 6.4 ml/min per kg and 0.38 l/kg, respectively, and the corresponding values for GBA were 2.4 h, 4.7 ml/min per kg and 1.01/kg respectively. 4. Radioactivity was rapidly distributed to most tissues after bolus i.v. doses of 14C-camostat mesylate to rats and dogs, with highest levels being associated with the liver and kidney, the two main organs of drug elimination. Concentrations in the pancreas, a possible site for drug action, were generally lower than those in plasma.

Percutaneous absorption of co-administered N-methyl-2-[14C]pyrrolidinone and 2-[14C]pyrrolidinone in the rat.

The percutaneous absorption has been investigated in rats of a mixture (3:2, w/w) of N-methyl-2-pyrrolidinone (NMP) and 2-pyrrolidinone (2-P), a combination intended for use as a vehicle in the formulation of an antimycotic drug to enhance skin penetration on dermal application, following co-administration of the two 14C-radiolabelled compounds by the dermal and oral routes. Radioactivity was excreted predominantly in the urine after either route of administration, and comparison of the respective excretion profiles indicated that about three-quarters of the applied dose was absorbed through the skin. Plasma concentrations of each parent compound, as determined by radio-HPLC, reached peak values at 2 hr after oral dosing, and remained relatively uniform during 1-6 hr after application to the skin, suggesting constant percutaneous absorption during this period. NMP appeared to be absorbed through the skin more extensively and at a slightly faster rate than 2-P; total percutaneous absorption tended to be more extensive in female than in male rats. Together, these two 14C-compounds accounted for most of the plasma radioactivity up to 6-8 hr post-administration. However, by 12 hr (when plasma levels were relatively low), most of the radioactivity was associated with unknown polar metabolites. In view of the extensive percutaneous absorption and little first-pass metabolism of the two pyrrolidinones, the oral route was considered to represent a valid alternative to the dermal route for the assessment of the systemic toxicity of the two compounds.

Metabolism and pharmacokinetics of the dihydropyridine calcium antagonist, ryosidine, in man.

The metabolic fate of [14C]ryosidine (ryodipine) has been investigated after oral administration to human subjects (by capsule), and to rats and dogs (in solution). The excretion patterns of 14C were similar for all three species: about 50% dose was excreted in urine, mainly in 24 h, but a proportion was excreted slowly, particularly by humans. Absorption in man appeared to be less than in the animal species, probably as a result of the capsule dosage form used. Mean concentrations of total 14C in human plasma reached a peak value of 0.41 microgram equiv./ml at four hours and declined biphasically thereafter (mean terminal t1/2 = 28 h). Unchanged ryosidine was only detected in plasma from two to six hours (mean t1/2 = 80 min), and never accounted for more than 5% of the plasma 14C. The extent of binding of ryosidine to the plasma proteins (in vitro) was similar (greater than 90%) to that of total 14C (in vivo; mainly metabolites). Less than 0.5% of the dose to human subjects was excreted via the kidneys as unchanged ryosidine, whereas the bulk of the extractable faecal 14C was in the form of unchanged drug and presumably represented unabsorbed material. The principal routes of biotransformation of ryosidine in all three species involved oxidative aromatization of the 1,4-dihydropyridine ring, followed by ester hydrolysis, O-dealkylation, hydroxylation of an alpha-methyl group (and lactonization) and some glucuronidation, although quantitative interspecies differences were apparent.

The metabolic fate of the anti-androgenic agent, oxendolone, in man.

After intramuscular administration of 16 beta-ethyl-17 beta-hydroxy-4-4-[4-14C]estren-3-one (14C-oxendolone; 300 mg) to 3 human subjects, excretion of 14C was very slow and incomplete despite a 20-day sample collection period. During this time, means of 37% and 21% of the administered 14C were recovered in urine and faeces, respectively, and if excretion continued at the same rate, approximately 90% of the administered 14C would have been excreted during 5-12 weeks. Peak plasma 14C concentrations were reached at 3-6 days after dosing, when they represented 0.2-1.1 micrograms equiv./ml, and declined very slowly thereafter with a half-life of 5.0-6.6 days. Concentrations of unconjugated drug-related steroids circulating in plasma never exceeded about 0.1 microgram/ml. Mass spectroscopic analysis of isolated urinary and faecal metabolites indicated that the principal routes of biotransformation of oxendolone in man are similar to those of the endogenous androgens-namely, reduction of the 4,5-double bond, further reduction of the saturated 3-ketone to the 3 alpha-hydroxysteroid, and oxidation of the 17 beta-alcohol to the corresponding ketone, followed by conjugation, mainly with glucuronic acid, and excretion in the urine and bile.

Biotransformation of lofexidine in humans.

1. Concentrations of unchanged drug and patterns of radioactive components in urine have been determined by h.p.l.c. following single oral doses of [14C]lofexidine hydrochloride (0.32 mg) to six human subjects. 2. A mean of 12% of the administered dose was excreted in urine as unchanged lofexidine, but the wide range (5-20% dose) indicated significant intersubject variation in the extent of biotransformation. This drug would appear to be metabolized more extensively than the related anti-hypertensive agent, clonidine. 3. The principal metabolite of lofexidine was 2,6-dichlorophenol, which was apparently excreted in urine as two O-glucuronic acid conjugates. The same two metabolites were also the main 14C components circulating in plasma at peak 14C concn. Formation of the phenol from lofexidine probably involved direct O-dealkylation rather than stepwise degradation of the side-chain. 4. Patterns of 3H components in the urine of rats and dogs after oral administration of [3H]lofexidine hydrochloride (0.1 mg/kg) were generally similar to those in human urine.

A novel conjugate as a major metabolite of bromperidol in man.

The major urine metabolites of the neuroleptic drug, bromperidol, after oral doses to rats and dogs are p-fluorophenylacetic acid and its glycine conjugate resulting from oxidative N-dealkylation. While the same metabolites were also detected in human urine, also present was a major unknown component representing 50% of the total urine metabolites, which apparently was not formed by rats and dogs to any extent. Mass spectroscopic investigations a substituent attached to the tertiary hydroxyl group. The mass spectrum of the metabolite after trifluoroacetylation was consistent with an O-glucofuranosiduronolactone conjugate of bromperidol.

The metabolic fate of 3[H]econazole in man.

1. Following single oral doses of 3[H]econazole base (500 mg) to two human subjects, excretion of radioactivity was prolonged, and incomplete after five days (means of 40% and 27% dose in urine and faeces respectively). 2. Plasma concn. of unchanged econazole and total radioactivity attained peak values at approx. the same for each subject (1.5 - 3h), but the former declined much faster than the latter. Most of the 3H in early plasma samples was present as unchanged drug and extractable metabolites, but after 24h concn. of econazole were close to the limit of detection (0.04 ug/ml) and very little plasma 3H was extractable, whereas total 3H concn. were still measurable after five days (mean 1.54 ug/ml). Thus, plasma contained metabolites with much longer half-lives than econazole. 3. The main route of biotransformation of econazole in man involved multiple oxidation of the imidazole ring carbons followed by O-dealkylation and conjugation of the resulting alcohols, probably with glucuronic acid.

Determination of amitriptyline and its major basic metabolites in human urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the routine, simultaneous determination of amitriptyline and its basic metabolites in human urine has been developed. 10-Hydroxylated metabolites are analyzed as their 10,11-dehydro analogs, and primary and secondary amines as their N-trifluoroacetyl derivatives. The use of gradient elution enables amitryptyline, nortriptyline trifluoroacetate, desmethylnortriptyline trifluoroacetate, and the corresponding 10, 11-dehydro analogs to be separated from both each other and from the internal standard used. In this way all six compounds may be conveniently measured in a single chromatogram, with good sensitivity and accuracy. Following administration of a single oral dose (25 mg) of amitriptyline hydrochloride to two human subjects, no unchanged drug was found in any of the urine samples analyzed up to 72 hr after dosing, and only small amounts of nortriptyline and desmethylnortriptyline were observed. 10-hydroxynortriptyline was the major biotransformation product (about 40% of the dose) in urine, with 10-hydroxyamitriptyline and 10-hydroxydesmethylnortriptyline present as minor metabolites. During 72 hr after administration, approximately 60% of the dose was recovered as these five metabolites.

The use of 13C-nmr spectroscopy for the detection and identification of metabolites of carbon-13 labelled amitriptyline.

The antidepressant drug amitriptyline and two of its metabolites, nortriptyline and desmethylnortriptyline, each containing two 13C atoms, have been used to determine the sensitivity and selectivity of 13C-nmr spectroscopy for the detection of unchanged amitriptyline and N-desmethyl metabolites in the urine of animals dosed orally with the labelled drug. The resonance signals from the 13C atoms detected in the 13C-nmr spectrum of entire extract from a control 12 h rat urine sample to which 1 mg of each labelled compound had been added were easily detected, using an instrument accumulation time of 1 h. The 13C-nmr spectrum of an extract of hydrolysed urine from a dog that had received an oral dose of [13C2]amitriptyline (30mg) exhibited signals that could be assigned to metabolites resulting from N-dealkylation and N-oxidation, as well as those bearing the intact amitriptyline side-chain. These assignments were confirmed by analysis of the same extract by g.c.--ms and h.p.l.c.