Pharmacokinetics, metabolism and excretion of the glycine antagonist GV150526A in rat and dog.

1. The pharmacokinetics, metabolic fate and excretion of 3-[-2(phenylcarbamoyl) ethenyl-4,6-dichloroindole-2-carboxylic acid (GV150526), a novel glycine antagonist for stroke, in rat and dog following intravenous administration of [C14]-GV150526A were investigated. 2. Studies were also performed in bile duct-cannulated animals to confirm the route of elimination and to obtain more information on metabolite identity. 3. Metabolites in plasma, urine and bile were identified by HPLC-MS/MS and NMR spectroscopy. 4. GV150526A was predominantly excreted in the faeces via the bile, with only trace metabolites of radioactivity in urine (< 5%). Radioactivity in rat bile was predominantly due to metabolites, whereas approximately 50% of the radioactivity in dog bile was due to parent GV150526. 5. The principal metabolites in bile were identified as glucuronide conjugates of the carboxylic acid, whereas in rat urine the main metabolite was a sulphate conjugate of an aromatic oxidation metabolite. Multiple glucuronide peaks were observed and identified as isomeric glucuronides and their anomers arising from acyl migration and muta-rotation.

In vivo metabolism of a novel cholecystokinin B (CCK-B) antagonist in rat and dog plasma and rat faeces.

1. The in vivo metabolism of a novel CCK-B antagonist ((+)-N-[1-(adamantane-1-methyl)-2,4-dioxo-5-phenyl-2,3,4,5-tetrahydro-1H -1,5-benzodiazepin-3-yl]-N'-phenylurea, GV150013X) was investigated using rat and dog plasma (male and female) and rat faeces samples after administration of GV150013X. 2. Four monohydroxy and four dihydroxy metabolites of GV150013X were identified by comparison with authentic standards using hplc and results from previous in vitro studies. 3. In both rat and dog plasma, GV150013X was converted to one major and other minor metabolites. 4. Qualitatively there is no species or sex differences in the formation of metabolites except that minor metabolite M1 was not detected in dog plasma. 5. Traces of GV150013X and the major metabolite were seen in rat plasma sample 24 h after administration. 6. Hplc with UV and radiochemical detection was used to identify metabolites. Major, non-labelled GV150013X metabolites from rat faeces were collected for characterization by nmr.

Metabolism of a novel CCK-B antagonist in rat, dog and human liver microsomes.

1. The in vitro metabolism of a novel CCK-B antagonist ((+)-N-[1-adamantane-1-methyl)-2,4-dioxo-5-phenyl-2,3,4,5-tetrahydro-1H- 1, 5-benzodiazepin-3-yl]N'-phenyl-urea; GV150013X) was investigated using rat, dog and human liver microsomes. 2. Four monohydroxy and four dihydroxy metabolites of GV150013X in rat and man were identified by comparison with authentic standards using HPLC and mass spectrometry. 3. The dihydroxy metabolite M1 was not detected in dog liver microsomes mixtures. 4. The formation of dihydroxylated metabolites proceeds via monohydroxylated metabolites M5 and M8 and not directly from GV150013X. 5. A monohydroxy metabolite M5 was the major metabolite in rat and dog, with M5 and dihydroxy metabolites M2 and M3 major metabolites in man.

In vitro metabolism of GV150013X by using liver microsomes and liver tissue slices from different species.

The metabolism of GV150013X was studied in vitro using washed liver microsomes and liver tissue slices from different species. This work was carried out in order to compare the metabolite profiles resulting from incubation of GV150013X with human, rat, dog and rabbit liver microsomes and those from rat, rabbit and human liver tissue slices. This compound was found to be converted to at least 8 metabolites by rat and human liver microsomes. In rabbit liver microsomes, the three metabolites M4, M7 and M8, and in dog liver microsomes metabolite M1, were not detected. The main metabolites, M2, M5 and M6, were present in human, rat and rabbit liver tissue slices, while the three metabolites M3, M4 and M8 and metabolite M1 were not detected in rabbit and rat liver tissue slices, respectively. In rat liver tissue slices, the major metabolites plus five minor metabolites, one sulphate conjugate of a monohydroxylated, three trihydroxylated and one dihydroxylated were identified based on HPLC retention time and thermospray-mass spectrometry data. Quantitative species differences among rat, dog, rabbit and human were observed, while qualitative differences only between rabbit and other species were detected.

Automation and validation of the high-performance liquid chromatographic-radioimmunoassay method for the determination of lacidipine in plasma.

The automation and validation of the HPLC-radioimmunoassay (RIA) method for the determination of lacidipine are reported. The solid-phase extraction step was automated by the introduction of the ASPEC system. A two-column system was adopted for the HPLC purification. The RIA was converted from heterogeneous to homogeneous by the scintillation proximity assay system and automated using an automatic dilution system. All characteristics in terms of accuracy, precision, specificity, and linearity resulted similar to the manual version. The quantification limit was set to 40 pg/ml. The new version of the method increased the number of samples assayed per month two- to three-fold.

A study of plasma disposition kinetics of lacidipine after single oral ascending doses.

This study was designed to assess the plasma disposition kinetics of single oral 4-, 6-, and 8-mg doses of lacidipine, a new once-daily calcium-entry blocker. Seventeen healthy volunteers attended the study. In almost all cases, detectable levels were found up to 24 h after the drug administration, using a new HPLC-RIA assay. The usual pharmacokinetic parameters were calculated: Cmax, tmax, AUCinf, lambda z and t1/2. The half-life was similar after all doses, around 7 h, whereas Cmax and AUCinf did not show a linear correlation with the doses.

Lacidipine metabolism in rat and dog: identification and synthesis of main metabolites.

1. The main metabolites of lacidipine were isolated from bile and plasma of rats and dogs following an oral dose of the 14C-labelled drug (10 mg/kg for rats: 2 and 1 mg/kg for dogs). They were identified by comparison of chromatographic and spectral data with authentic reference compounds synthesized ad hoc. 2. Five metabolites (I-V) were isolated and identified in dog bile by gradient h.p.l.c. with u.v. detection and h.p.l.c.-thermospray mass spectrometry. In all metabolites the heterocyclic ring has been oxidized to pyridine. Further biotransformation reactions involved hydroxylation of the methyl substituents and hydrolysis of the ethyl and t-butyl ester groups to produce carboxylic acids and a lactone. Some of these metabolites also occurred as glucuronide conjugates. 3. A metabolite retaining the intact dihydropyridine ring, the des-ethyl analogue of lacidipine (VI), was isolated from rat plasma where it accounted for 60% of the total circulating radioactivity up to 24 h after administration. To characterize this metabolite, h.p.l.c. with photodiode array u.v. detection also was employed. This compound was detected in dog plasma, but there was no evidence of its presence in dog bile samples. 4. Profiles of circulating metabolites were qualitatively similar in rats and dogs. Identified metabolites accounted for the large majority of total radioactivity in all the analysed samples.

Validation of a high-performance liquid chromatographic-radioimmunoassay method for the determination of lacidipine in plasma.

A sensitive and reproducible method for the determination of lacidipine, a new potent antihypertensive dihydropyridine, is reported. The method involves solid-phase extraction, reversed-phase high-performance liquid chromatography and radioimmunoassay of the collected fraction. The assay provides a limit of detection of 20 pg/ml of plasma, allowing the determination of trough (24 h) plasma concentrations. The method is suitable for pharmacokinetic studies in man.

The pharmacokinetic and pharmacodynamic interaction between lacidipine and propranolol in healthy volunteers.

The pharmacokinetic and pharmacodynamic profiles of lacidipine, a 1,4-dihydropyridine calcium antagonist, and the beta-adrenoceptor blocker propranolol were determined alone and in combination in 24 healthy male volunteers. One group (I) of 12 subjects received a single oral dose of 4 mg lacidipine on two separate occasions, which was taken together with a single oral dose of either 160 mg propranolol or placebo; a second group (II) of 12 subjects received propranolol on two occasions, taken with either lacidipine or placebo. Propranolol significantly decreased the maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) of lacidipine (by 38% and 42%, respectively) whereas lacidipine significantly increased the Cmax and AUC of propranolol (by 35% and 26%, respectively); neither the time to maximum plasma concentration (tmax) nor the terminal half-life (t 1/2) were affected. With regard to the pharmacodynamics, in Group I, there was a greater reduction in supine systolic blood pressure (6 mm Hg) and diastolic blood pressure (4 mm Hg) compared to the reduction produced by lacidipine alone, and pulse rate was approximately 5 beats/min less. In Group II, a significantly greater reduction (6 mm Hg) in supine systolic blood pressure compared to the reduction produced by propranolol alone occurred, but there was no marked difference in supine diastolic blood pressure and pulse rate. In conclusion, a modest pharmacokinetic and pharmacodynamic interaction is evident and should be evaluated further in patients with hypertension.

Clinical pharmacology of lacidipine.

The safety and tolerability of lacidipine was assessed in a volunteer population, and its pharmacodynamic and pharmacokinetic profiles evaluated. In normotensive subjects, single oral doses of 3-5 mg of lacidipine produced a dose-related fall in peripheral vascular resistance. This was accompanied by reflex-mediated increases in heart rate and cardiac output to maintain blood pressure. Adverse events were those typically related to the vasodilatory action of lacidipine, such as flushing and headache. A 4-mg dose of lacidipine elicited a cardiovascular response equivalent to that with 10 mg of nifedipine, given as a single oral dose. Lacidipine did not affect sinoatrial or atrioventricular conduction in the healthy subjects studied. Two specialized electrophysiologic studies in patients confirmed that lacidipine does not affect pacemaker tissue and that it exhibits relative selectivity for the vascular smooth muscle. Lacidipine is eliminated primarily by hepatic metabolism, and extensive first-pass loss occurs after oral dosing. Absolute bioavailability is less than 10%. The systemic availability of lacidipine was increased in healthy elderly subjects and in patients with impaired hepatic function, but not in patients with impaired renal function.

Absorption, distribution and excretion of lacidipine, a dihydropyridine calcium antagonist, in rat and dog.

1. The absorption, distribution and excretion of lacidipine have been studied in rat and dog after i.v. (0.05 mg/kg for rat; 0.5 mg/kg for dog) and oral dosage (2.5 mg/kg for rat; 2.0 mg/kg for dog). 2. Lacidipine was rapidly and extensively absorbed after oral dosing, in both species. Oral bioavailability was up to 26% in rat and up to 32% in dog, due to extensive first-pass metabolism. 3. After oral administration, peak levels of radioactivity were reached at 4-8 h in rat and 1-2 h in dog. Unchanged lacidipine peaked at 1-2 h in both species. Plasma levels of radioactivity were higher in female rats than in males but there was no difference in levels of unchanged drug. 4. After i.v. dosing the terminal half-life of unchanged drug was 2.9 h in rat and 8.2 h in dog. The half-life of radioactivity in plasma was longer in both species. 5. After both routes of administration, radioactivity was rapidly distributed in rat tissues with the highest concentration in liver, fat and gastrointestinal tract. Only traces of radioactivity were detected in the CNS and in rat foetuses. 6. Extensive biliary elimination occurred, and most of the radioactivity (73-95%) was excreted in the faeces after i.v. or oral administration. 7. The compound was extensively metabolized, no significant amount of unchanged drug was excreted in bile or urine.

Effect of ranitidine on the absorption of aspirin.

Six healthy male volunteers received 1 week's pretreatment with ranitidine, 150 mg twice daily, and placebo in a double-blind cross-over trial. On the 8th day, each volunteer received 1 g of aspirin in order to study the pharmacokinetics of this nonsteroidal anti-inflammatory drug. The results of this study suggest that ranitidine does not induce clinically significant alterations to the kinetics of a single dose of aspirin in healthy males.

[14C]cadralazine: absorption, distribution and excretion in rat and dog.

Absorption, distribution and excretion of [14C]cadralazine in rat after oral and i.v. administration of 3 mg/kg were studied. Plasma levels after oral administration of 10 and 45 mg/kg were also evaluated. A direct relation between dose and plasma levels was demonstrated. The drug was well absorbed, disappeared very rapidly from plasma, and was distributed in all the organs examined, with the highest concentration in liver, kidney, and gastrointestinal tract. For more than 4 days excretion was essentially through the urine (75.6% after i.v. and 80% after oral administration), whereas faecal and biliary excretions were quite low. The total recovery was respectively 77.6% and 83.2% after i.v. and oral administration of 3 mg/kg, with the greatest amount (65-70% of the administered dose) appearing in the first 4 to 7 hours. Placental transfer and excretion of radioactivity with milk were demonstrated. Drug-protein binding was 25.9%. Elimination of 14CO2 was not observed. Plasma levels in dog, after oral and i.v. administration of 1 mg/kg of labelled compound, showed similar behaviour to that observed in the rat. Binding of the radioactivity to erythrocytes was found; the radioactivity values observed up to 24 hours were constant with time and not dependent on the decreasing plasma levels. The total recovery (urine and faeces) in the dog over 4 days was 71.1% and 82.1% after oral and i.v. dose, respectively. Preliminary metabolic approaches in rats showed that cadralazine was essentially excreted as unchanged drug in the presence of minor metabolites.