Pharmacokinetics and hypotensive effect of deacetyl N-monodesmethyl diltiazem (M2) in rabbits after a single intravenous administration

Deacetyl N-monodesmethyl diltiazem (M2) is a major metabolite of the widely used calcium antagonist diltiazem (DTZ). In order to study the pharmacokinetic and haemodynamic effects of this metabolite, M2 was administered as a single 5 mg/kg dose intravenously (i.v.) to New Zealand white rabbits (n = 5) via a marginal ear vein. Blood samples, blood pressure (SBP and DBP), and heart rate (HR) recordings were obtained from each rabbit up to 8 h, and urine samples for 48 h post-dose. Plasma concentrations of M2 were determined by HPLC. The results showed that there were no identifiable basic metabolites which could be quantified and characterized in the plasma. The apparent terminal t1/2 and AUC were 2.8 +/- 0.7 h and 2000 +/- 290 ng x h/ml, respectively. The Cl and Clr of M2 were 38 +/- 4.8 ml/min/kg and 0.57 +/- 0.23 ml/min/kg, respectively. M2 significantly decreased blood pressure (SBP and DBP) for up to 2 h post-dose (P < 0.05), but had no significant effect on the heart rate (P > 0.05). The Emax and EC50 as estimated by the inhibitory sigmoidal Emax model were 15 +/- 7% and 450 +/- 46 ng/ml, respectively, for SBP; 15 +/- 20% and 430 +/- 120 ng/ml for DBP.

Effect of diltiazem on plasma concentrations of oxypurines and uric acid

To determine the clinical effect of diltiazem on the metabolism of adenosine, and its importance in ischemic heart disease, arterial plasma concentrations of the purine metabolites were determined in 21 healthy volunteers (10 female and 11 male) and 19 patients with effort angina (8 female and 11 male) before, during, and immediately after standard treadmill exercise tests conducted before and after they had taken 60 mg diltiazem (Cardizem; Hoechst Marion Roussel, Laval, QC, Canada) four times a day for 1 week. The results showed that the cardiac patients had significantly lower mean plasma concentrations of uric acid (46.82 +/- 25.51 versus 95.47 +/- 35.41 micrograms/ml, p 0.05), inosine (0.25 +/- 0.19 versus 0.84 +/- 0.17 microgram/ml, p < 0.05), and hypoxanthine (0.28 +/- 0.35 versus 0.50 +/- 0.27 microgram/ml, p < 0.05). Diltiazem decreased the mean resting plasma concentrations of uric acid in patients (uric acid 43.47 +/- 22.26 versus 46.82 +/- 25.51 micrograms/ml, p < 0.05) and healthy volunteers (uric acid 85.68 +/- 26.71 versus 95.47 +/- 35.41 micrograms/ml, p < 0.05). There was no statistically significant change in the plasma concentrations of the purine metabolites during exercise (p < 0.05). Female subjects had significantly lower plasma concentrations of uric acid than males (patients, 34.87 +/- 26.93 versus 55.78 +/- 21.25 micrograms/ml; healthy volunteers, 84.79 +/- 32.07 versus 104.22 +/- 37.05 micrograms/ml; p < 0.05 for both). Results of the study suggest that normal therapeutic doses of diltiazem may modulate the metabolism of adenosine and that some of the purine metabolites may be useful markers for specific types of ischemic heart disease.

Effect of diltiazem on intraarterial blood pressure and heart rate during stress testing in patients with angina: a gender comparison study

The purpose of this study was to measure the blood pressure and electrocardiographic responses of a small, matched group of women (n = 8) and men (n = 9) who experienced typical, effort angina during an exercise on the treadmill (up to the second stage of a Bruce protocol). These responses were measured before and after therapy with diltiazem (60 mg four times daily for 1 week). Reports of previous studies have described significant gender differences in blood pressure responses to diltiazem in healthy volunteers tested with the same protocol. In contrast to the data in healthy individuals, gender differences in blood pressure responses to exercise before and after diltiazem administration were not observed. Results of analysis of pulse pressure responses to exercise were also similar in male and female patients with angina. A significant postexercise drop in blood pressure was observed, which was augmented by diltiazem. These data suggest that gender differences in drug action may be difficult to demonstrate in patients with vascular disease.

Sequence data for two large-subunit rRNA genes from an Asian strain of Alexandrium catenella

PCR generated two distinct products from a toxic isolate of Alexandrium catenella, which had been taken from Dai Ya Bay (southern China), by using primers for large-subunit rRNA. This pattern is distinct from published data for North American Alexandrium species. Sequences of the two products suggest that the smaller was generated by a deletion event. Single-cell PCR generated the same pattern, confirming that the two products were not the results from different individuals.

Effect of omeprazole on movement of intravenously administered metronidazole into gastric juice and its significance in treatment of Helicobacter pylori

Four healthy, Helicobacter-negative volunteers were studied to determine the effect of omeprazole on the movement of metronidazole across the gastric mucosa into the gastric lumen. Each received a 500-mg intravenous infusion of metronidazole and repeated serum, and gastric juice samples were obtained concomitantly over an 8-hr study via indwelling intravenous catheter and nasogastric tube. The same protocol was repeated following one week of oral omeprazole 20 mg twice daily. Metronidazole concentrations were measured by high-performance liquid chromatography. The results demonstrated that: metronidazole moves rapidly from serum into gastric juice; omeprazole causes a marked reduction in total metronidazole concentrations in gastric juice, completely accounted for by pH-related shifts in the proportion of ionized metronidazole, but does not alter concentrations of nonionized metronidazole, which remain above the MIC level against H. pylori; and even under conditions where no pH-related drug trapping occurs (pH > 4), concentrations of metronidazole were higher in gastric juice than in serum during most of the study, indicating that a special transport mechanism may be operational. The practical implication of this effect of omeprazole in combination therapy with metronidazole remains to be established.

Determination of 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid in human plasma by a simple and rapid high-performance liquid chromatography assay

In order to study the pharmacodynamic effects of drugs on dopamine and serotonin metabolism, a reversed-phase HPLC assay coupled with electrochemical detection (ECD) for measuring plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) was developed. The system was operated isocratically using a mobile phase of aqueous 0.03 M KH2PO4 buffer containing 0.15 mM EDTA in methanol (8.75:1.25), with a final pH of 4.0. The flow rate was set at 1.5 mL/min, and potentials at +450 mV. Using a signal to noise ratio of > 3, the minimum detection limit assessed by direct on-column injection of a standard solution for DOPAC and 5-HIAA was < 1 pg. The assays were linear from basal concentrations (1-10 ng/mL) to 100 ng/mL. The intra- and interassay variations were < 10% and < 20%, respectively.

Steady-state plasma concentrations of diltiazem and its metabolites in patients and healthy volunteers

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and hypertension. It is extensively metabolized in humans via N-demethylation, O-demethylation, deacetylation, and oxidative deamination, yielding a host of metabolites, some of which have potent pharmacological properties. After our initial identification of O-desmethyl DTZ (Mx) and N,O-didesmethyl DTZ (MB) as major metabolites of DTZ and our subsequent of identification of their chemical synthesis, an improved high-performance liquid chromatography assay was developed to determine the plasma concentrations of DTZ and seven of its major basic metabolites, including the previously unquantitated Mx and MB. The system consisted of a C18 analytical column protected by a C18 cartridge guard column and a variable wavelength ultraviolet detector set at 237 nm. The mobile phase was a mixture of methanol, 0.04 M ammonium acetate, and acetonitrile (38:36:26) containing 0.08% triethylamine, with final pH of the mobile phase adjusted to 7.5. The system was operated at room temperature isocratically at a flow rate of 1.2 ml/min. Using verapamil as an internal standard, DTZ and the basic metabolites in plasma were determined in young healthy volunteers (n = 21) and in patients with ischemic heart disease (n = 19) at steady state after repeated oral doses of 60 mg DTZ four times daily. Preliminary results show that steady-state plasma concentrations of DTZ and its metabolites were higher in the older patients than in young healthy subjects (p < 0.05).

Effect of phenobarbital pretreatment on the pharmacokinetics and metabolism of diltiazem in rats

In order to study the effect of cytochrome P-450 isozyme induction on the pharmacokinetics and metabolism of diltiazem (DTZ), male Sprague-Dawley rats weighing 300-600 g were randomly assigned to two groups. The enzyme induction group (n = 4) received phenobarbital 60 mg/kg i.p. once daily for 4 days, whereas the control group (n = 6) received normal saline for the same duration. Each rat then received a single oral dose of DTZ in solution (20 mg/kg). Blood samples (0.5 ml) were collected from each rat via an implanted polyethylene catheter (0.040" i.d.) in the right carotid artery at 0 (just before dosing), 0.25, 0.5, 1,2,3,4,6,8 and 10 h post-dose. Arterial plasma concentrations of DTZ and its metabolites M(A), M1, M2, M4 and M6 were determined by HPLC. Pharmacokinetics parameters were calculated using non-linear regression. The results showed that both mean Cmax and AUC of DTZ were lower (871.6 vs 79.8 ng/ml; 1171 vs 101.9 ng-h/ml), but the mean Cmax of the primary metabolites M1 and M(A) was higher after phenobarbital (M1 413.0 vs 648.9 ng/ml; M(A) 683.0 vs 814.8 ng/ml). The highest increase was seen in the mean Cmax and AUC of the secondary metabolite M2 (837.5 vs 2585.7 ng/ml; 3312.1 vs 13156.5 ng-h/ml). In contrast, plasma concentrations of the O-desmethylated metabolites M4 and M6 did not increase after phenobarbital. These results suggest that both deacetylation and N-demethylation of DTZ in rats are catalyzed by drug metabolizing enzymes inducible by phenobarbital.

Pharmacokinetics and metabolism of diltiazem in rats following a single intra-arterial or single oral dose

Diltiazem (DTZ) 20 mg/kg was given to male Sprague-Dawley rats either orally (p.o.) or intra-arterially (i.a.) over a 5 min period (n = 6 for each group). Plasma concentrations of DTZ and its major basic metabolites were determined by high performance liquid chromatography assay (HPLC) as previously described over a 10 h period. The major metabolites found in the rat plasma were M2, followed by M6, MA, M1, and then M4. The metabolite Mx was measurable only in some of the plasma samples, and MB was not detected in this species. The mean apparent half-life (t1/2) of the measurable metabolites were longer than the parent DTZ. The metabolism profiles were qualitatively similar between the two routes of administration. Quantitatively, however, the plasma concentrations of the metabolites were higher after the i.a. route. These results are in agreement with a previous study reported in rabbits, and suggest that deacetylation of DTZ and MA in the blood is extremely important in this species.

The effect of multiple doses of ranitidine on the pharmacokinetics and metabolism of diltiazem in dogs

In order to determine the potential pharmacokinetic drug interaction between ranitidine and diltiazem (DTZ), each of ten male beagle dogs, age 2.7-4.0 years, weight 13-16 kg, received a single oral dose of sustained release DTZ with and without previous multiple oral doses of ranitidine (150 mg bid for five doses). The dog was selected as the animal model because the pharmacokinetics and metabolism profiles of DTZ are similar to those in humans and because sustained release DTZ capsules can be administered with ease to this species. Following the oral dose of DTZ, blood samples (5 ml each) were obtained via a cephalic vein at 0 (just before dosing), 1, 2, 3, 4, 5, 6, 8, 12, 18, 24, 30, 36, and 48 h after the dose. Urine samples were collected for 48 h post dose. Plasma and urine concentrations of DTZ and its major metabolites N-monodesmethyl DTZ (MA), deacetyl DTZ (M1), and deacetyl N-monodesmethyl DTZ (M2) were determined by HPLC. Pharmacokinetic parameters were calculated by non-linear curve fitting, and the effect of ranitidine was evaluated by two-factor analysis of variance (ANOVA). Pre-treatment of the animals did not significantly alter the disposition of DTZ (p > 0.05). Similar to the results reported in clinical studies, there were large variations in the plasma and urine concentrations of DTZ and its major metabolites among the beagle dogs. The effect of ranitidine on the disposition of DTZ was highly variable.

Pharmacokinetics of chlorpromazine and key metabolites

A study was carried out in 11 healthy young men to investigate the pharmacokinetics of chlorpromazine (CPZ) after a bolus intravenous (i.v.) dose (10 mg) and three single oral doses (25, 50 and 100 mg), with a washout period of two weeks between doses. Plasma levels of CPZ, CPZ N-oxide (CPZNO), CPZ sulfoxide (CPZSO) and both free and conjugated 7-hydroxy-CPZ (7-HOCPZ) were measured by extraction radioimmunoassays. CPZ exhibited multicompartmental pharmacokinetics in most subjects. There was wide between-subject variability in half life (11.05 h), volume of distribution (1215 l), volume of distribution at steady state (642 l) and mean residence time (8.88 h), whereas systemic clearance was somewhat less variable (76.6 l.h-1). All metabolites were present in measurable concentrations in the plasma of 9 of 11 subjects after i.v. CPZ, whereas free 7-HOCPZ was not detected in the other 2 individuals. With the exception of CPZNO, the biological half lives of the primary metabolites were longer than the half life of CPZ. After oral administration, the percentage of CPZ reaching the systemic circulation intact (F%) was very low (4-38%) and dose dependent. Moreover, both within-subject and between-subject variances were very high. The maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve extrapolated to infinite time (AUC) showed evidence of nonlinearity, whereas half life did not appear to be dose dependent. These data suggest that the high degree of variability in the pharmacokinetics of CPZ is a result of extensive first pass metabolism rather than variation in half life.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte adenosine transport. A rapid screening test for cardiovascular drugs

An erythrocyte (RBC) model based on whole blood was used to investigate the effect of cardiovascular drugs on the uptake of adenosine in vitro. Fresh whole blood obtained from healthy volunteers was allowed to equilibrate with various concentrations (5-1000 microM) of a tested agent. (2-3H)-Adenosine was used as a substrate, and the reaction was terminated after 2 sec of incubation at room temperature by rapid addition of a "Stopping Solution" which was a mixture of erythro-9-(2-hydroxy-3-nonyl)adenine, dipyridamole, and EDTA. The mixture was centrifuged (1760 g, 4 degrees C, 10 min), and the radioactivity of an aliquot of the supernatant was determined by a scintillation counter. The results showed that dipyridamole was the most potent agent tested (IC50 = 0.2 microM). Amongst the calcium antagonists studied, isradipine was most potent, followed by verapamil, clentiazem, diltiazem, and then nifedipine. The racemates of two metabolites of diltiazem, MX and MB, were more potent than the parent drug. The antiarrhythmic agents, amiodarone and sotalol, the two new lipid peroxidation inhibitors, U-74389F and U-78517F, and the anxiolytic agent, alprazolam, were as active as verapamil. The beta-receptor antagonist propranolol and the angiotensin converting enzyme (ACE) inhibitor, enalapril, were practically inactive. In addition, the model was stereoselective such that the S(-)-enantiomer of verapamil was considerably more potent than the R(+)-antipote, whereas d(+)-sotalol was practically inactive compared to racemic sotalol.

Pharmacokinetics and metabolism of diltiazem in healthy males and females following a single oral dose

Plasma concentrations and urinary excretion of DTZ and its metabolites were determined in 20 healthy volunteers (10 males and 10 females) after they had each been given a single oral 90 mg dose of DTZ. DTZ and six of its metabolites which included N-monodesmethyl DTZ (MA), deacetyl DTZ (M1), deacetyl N-monodesmethyl DTZ (M2), deacetyl O-desmethyl DTZ (M4) and deacetyl DTZ N-oxide (M1NO) and deacetyl N,O-didesmethyl DTZ (M6), were determined by a sensitive and specific HPLC assay. The major metabolites measurable in the plasma of all the volunteers were MA, M1, and M2. The terminal half-lives (t1/2) of M1 and M2 were considerably longer than those of DTZ and MA. Less than 5% of the dose was excreted as unchanged DTZ in the urine over the 24 h period. The major urinary metabolite was MA, followed by M6, M2, and then M1. Except for the urinary excretion of M4 there were no statistically significant differences in any of the pharmacokinetic parameters between the males and the females. The mean 24 h urinary recovery of M4 was higher in the males than in the females (P < 0.05). However there were large inter-individual variations in the plasma concentrations and urinary excretion of DTZ and its metabolites with some parameters differing by more than 20-fold. In addition, O-desmethyl DTZ (Mx) and N,O-didesmethyl DTZ (MB) were identified as two other major urinary metabolites.

Synthesis, characterization, and Ca2+ antagonistic activity of diltiazem metabolites

Diltiazem is a calcium antagonist widely used in the treatment of angina and hypertension. The contributions of metabolites of diltiazem to the vasorelaxant effects of diltiazem were investigated. The synthesis and spectroscopic characterization of eight major cis-diltiazem metabolites are described. Three of the compounds--N, O-didemethylated metabolite (21), O-demethylated metabolite (22), and diltiazem N-oxide (27)--have been recently reported and have not previously been synthesized. The identities of all eight synthetic metabolites have been verified with samples obtained from human urine using combined LC-MS/MS. The Ca2+ antagonistic activities of diltiazem and its metabolites (except 27) were studied on hamster aorta preparations depolarized with KCl. The order of potencies (IC50 +/- SE, microM) is as follows: diltiazem (0.98 +/- 0.47) greater than 17 (2.46 +/- 0.38) greater than or equal to 23 (3.27 +/- 1.02) greater than 26 (20.2 +/- 10.5) greater than 22 (40.4 +/- 15.4) greater than or equal to 25 (45.5 +/- 18.1) greater than 21 (112.2 +/- 33.2) greater than or equal to 24 (126.7 +/- 24.2). Structure-activity relationships are also discussed.

Effect of diltiazem and its metabolites on the uptake of adenosine in blood: an in-vitro investigation

Using whole blood from man and rabbits, the effect of diltiazem, its metabolites, and other calcium antagonists on the uptake of adenosine has been described. The uptake and metabolism of adenosine was extremely rapid with a half-life in plasma of less than 30 s. Adenosine is rapidly and extensively metabolized to hypoxanthine. Metabolites of diltiazem, deacetyl diltiazem and deacetyl O-desmethyl diltiazem were considerably more potent than the parent drug. Diltiazem was one-tenth as active as verapamil, but more active than nifedipine or amlodipine. Dipyridamole was the most potent uptake-inhibitor tested (IC50 less than 1 microM), whereas the angiotensin converting enzyme inhibitor enalapril was virtually devoid of any inhibitory activities (IC50 greater than 1000 microM). The results obtained from both man and rabbit were similar.

A reliable technique for chronic carotid arterial catheterization in the rat

A reliable and simple method for cannulating the carotid artery of rats is described. The rat was anesthetized with halothane. The right carotid artery located between the omohyoideus and sternohyoideus muscles was exposed through a 2-cm ventral neck incision. The catheter was made of Silastic tubing and a monofilament line, which served as an obturator and internal support. The line was then filled with a viscous mixture of heparin, polyvinylpyrrolidinone and normal saline to prevent the formation of blood clots. The catheter was advanced through the carotid artery towards the heart by a predetermined distance (15-20 mm) depending on the size of the rat. The catheter was well tolerated by the rats and the success rate was 95%. Its patency lasted for at least 7 days postsurgery without any special maintenance care. With the described method one would be able to perform repetitive blood sampling and arterial blood pressure measurements in unanesthetized and unrestrained rats for prolonged period after catheterization.

Stability of diltiazem and its metabolites in plasma during storage

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and related heart diseases. It is extensively metabolized into a host of metabolites, some of which have potent pharmacological activities. Previous work has shown that DTZ and its major metabolite N-desmethyl-DTZ (MA) were unstable and readily decomposed to deacetyl-DTZ (M1) and deacetyl N-desmethyl-DTZ (M2), respectively. This report describes the stability of DTZ and its metabolites in plasma samples stored at -20 and -70 degrees C for different periods up to 12 weeks. The results indicate that in those samples obtained from volunteers who received DTZ, no deterioration of DTZ or MA occurred up to 8 weeks, but considerable deterioration of DTZ to M1 and MA to M2 (p less than 0.01) occurred after 12 weeks. However, in samples prepared by adding DTZ and its metabolites to outdated plasma (spiked plasma), deterioration of DTZ occurred after 4-6 weeks of storage, but there were no concomitant increases in concentrations of M1 or M2. Thus, it appears that decomposition of DTZ and MA was affected by the nature of the plasma materials, but the reason for the differences in analyte stability observed between volunteers' and spiked plasma is not known. Also, it appeared that DTZ and its metabolites in plasma samples stored at -70 degrees C may be more stable than those at -20 degrees C, although further studies are required to substantiate this observation. On the basis of these results, plasma samples obtained from patients or volunteers receiving DTZ should be analyzed within 8 weeks when the samples are stored frozen at -20 degrees C.

Pharmacokinetics and metabolism of diltiazem in rabbits after a single intravenous or single oral administration

Diltiazem (DTZ) 5 mg/kg was given to rabbits either orally (n = 5) or intravenously (n = 6). Plasma concentrations and urinary excretion of DTZ and its metabolites were determined by a high performance liquid chromatography assay (HPLC) for 12 and 48 h post dose, respectively. The results showed that the metabolism and disposition of DTZ in rabbits was similar to that of humans, mean absolute bioavailability (F) of DTZ was approximately 30% and the systemic clearance was 64.0 ml/min/kg. The metabolism of DTZ between the two routes of administration was quantitatively different in that higher plasma concentrations of the metabolites were observed after the intravenous dose. This could be a result of incomplete oral absorption, higher clearance of DTZ and the metabolites during the first pass through the liver (i.e. higher sequential first pass effect), and/or extrahepatic metabolism. On the basis of the plasma concentration-time profiles and urinary excretion of DTZ and its metabolites, it is concluded that the rabbit is a suitable animal model to investigate the kinetics and metabolism of DTZ.

Liquid chromatography assay for amlodipine: chemical stability and pharmacokinetics in rabbits

Amlodipine is a long acting dihydropyridine calcium antagonist recently introduced for the treatment of angina and hypertension. In order to document its stability in vitro and to develop a pharmacokinetic model in rabbits, a new reversed-phase liquid chromatography (LC) assay with UV detection was developed. The method utilized a C18 column (250 x 4.6 mm i.d.) with a mobile phase composed of a mixture of methanol 0.04 M ammonium acetate-acetonitrile (38:38:24, v/v/v) containing 0.02% triethylamine (final pH 7.1). Under these conditions, the retention times of amlodipine and the internal standard desipramine were 10.6 and 12.9 min, respectively. Using 1 ml of plasma, sensitivity of the assay was 2.5 ng ml-1 at which the RSD was 11%. The standard curve was linear from 2.5 to 100 ng ml-1 (r2 = 0.990), and the mean RSD at this concentration range was 6.8%. The pharmacokinetic model was developed in rabbits which provides results similar to those in dogs, but at less expense. The assay was also applied to a stability study comparing amlodipine and nifedipine in pH 3 and pH 7 ammonium acetate buffers and in methanol. Amlodipine was considerably more stable than nifedipine under all conditions. Finally the assay was applied to a pharmacokinetic study in rabbits (n = 6) after a single 1 mg kg-1 intravenous dose. The mean half-life (t1/2) of amlodipine was 6.5 h, the systemic clearance (CL) was 4.8 l h-1 kg-1 and the apparent volume of distribution at steady state (Vdss) was 30.2 l kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Species comparison of pharmacokinetics and metabolism of diltiazem in humans, dogs, rabbits, and rats

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and related heart diseases. It is extensively metabolized into a host of metabolites, some of which have potent pharmacological activities. In this study, the pharmacokinetics and metabolism of DTZ was investigated in humans, dogs, rabbits, and rats after each species (n = 4 or 5) was given a single oral dose of DTZ. After the drug administration, blood and urine samples were collected for 12 and 48 hrs, respectively. DTZ and six of its metabolites were quantitated in our laboratory by HPLC. The results indicated that, in humans, the major metabolites in plasma were N-monodesmethyl diltiazem (MA), deacetyl diltiazem (M1), and deacetyl N-monodesmethyl diltiazem (M2). These metabolites were also detected in the plasma of dogs, rabbits, and rats. However, there were quantitative differences. For example, in the humans and dogs, MA was the most abundant metabolite in plasma, while M1 and M2 were most prominent in the rabbits and rats, respectively, and M2 was a relatively minor metabolite in dog plasma. Less than 5% of the dose was recovered as unchanged DTZ in the urine of all the tested species. The most abundant metabolites in urine appeared to be MA and deacetyl N,O-didesmethyl diltiazem, although there were considerable inter- and intra-species variations. Two additional metabolites were detected in the urine of the humans, dogs, and rabbits, but not in the rats. They were tentatively identified as O-desmethyl diltiazem and N-O-didesmethyl diltiazem, using electron impact and ammonia chemical ionization mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic assay of diltiazem and six of its metabolites in plasma: application to a pharmacokinetic study in healthy volunteers

A sensitive and specific reversed-phase high-performance liquid chromatographic assay for simultaneous determination of plasma concentrations of diltiazem and six of its metabolites known to occur in humans is reported. Using 2 mL of plasma, the lower limit of quantitation of the assay was less than 10 ng/mL of diltiazem and each of the metabolites, with coefficients of variation of less than 10%. The assay was successfully applied to determine the kinetics of diltiazem and its major metabolites in four healthy volunteers after each received a single 90-mg oral dose of diltiazem. In addition to the previously reported two major metabolites in humans, deacetyl diltiazem (M1) and N-monodemethyl diltiazem (MA), another previously unreported major metabolite, deacetyl N-monodemethyl diltiazem (M2), was present at comparable concentrations to M1 and MA in all four volunteers. In addition, another metabolite, deacetyl diltiazem N-oxide (M1-NO), which was previously found most abundant in urine, was also estimated in the plasma of two volunteers. Two other known human metabolites, deacetyl O-demethyl diltiazem (M4) and deacetyl N,O-didimethyl diltiazem (M6), were not detected in any of the four study subjects. The average maximum plasma concentrations of M1, M2, MA, and M1-NO were 10, 15, 26, and 13%, respectively, of the mean maximum diltiazem concentrations.