Pharmacokinetics of diltiazem in patients with unstable angina pectoris

Effect of concomitant colestipol hydrochloride administration on the bioavailability of diltiazem from immediate- and sustained-release formulations

Effects of concomitant colestipol administration on plasma concentrations of diltiazem and desacetyldiltiazem from immediate-release (IR) and sustained-release (SR) formulations were assessed in two studies. In the first study, 12 subjects received 120-mg diltiazem hydrochloride (diltiazem) SR capsules or 120-mg diltiazem IR tablets administered alone and in combination with colestipol hydrochloride (colestipol). Following concomitant administration of SR diltiazem with colestipol, AUC(0-infinity ) and C(max), respectively, were 22 and 36% less, and were 27 and 33% lower for IR diltiazem. In the second study, subjects received 120-mg diltiazem SR capsules at staggered times, without colestipol, 1 h prior to or 4 h following multiple doses of colestipol. A 17% decrease in AUC(0-infinity ) was observed when diltiazem was taken 1 h before colestipol was given, and a 22% decrease when diltiazem was taken 4 h after colestipol, relative to diltiazem SR alone. C(max) values were similarly decreased. Results from these two studies show that colestipol can cause a significant decrease in diltiazem absorption from both IR and SR dosage forms. Staggering the administration of colestipol and diltiazem SR did not blunt this effect, indicating that concomitant administration of diltiazem and colestipol should be used with caution, and that the efficacy of diltiazem should be monitored to assure adequate dosing.

Diltiazem disposition and metabolism in recipients of renal transplants

Diltiazem is widely prescribed in Australasia as a cyclosporine-sparing agent. On seven separate occasions at 2-week intervals, the authors studied eight patients who had undergone renal transplantation, were treated with cyclosporin A, and were in stable condition. The patients were administered escalating doses of conventional-release diltiazem, and (in an extension study) controlled-diffusion diltiazem, to consider the disposition and metabolism of diltiazem. Blood samples were drawn during a 24-hour period, and the AUC(0)(24) of diltiazem and three major metabolites was determined. Results demonstrated that seven patients had comparable diltiazem metabolite AUC(0)(24) profiles, despite considerable variability in parent diltiazem areas under the curve (AUCs), with DM-DTZ > DA-DTZ > DMDA-DTZ. The eighth patient displayed a different metabolite profile. The controlled-diffusion formulation reduced the interpatient variability in diltiazem AUC(0)(24) from 46-fold to <3-fold, but it did not appear to have release characteristics consistent with the manufacturer's specifications. The apparent bioavailability of the conventional-release diltiazem formulation appeared to be highly variable, and this has implications for its use in recipients of organ transplants. The dosage escalation demonstrated a linear relationship between dose and AUC for diltiazem and for each of the metabolites. There may be a subset of patients who display a different diltiazem metabolite profile.

Effects of cardiovascular drugs on ATPase activity of P-glycoprotein in plasma membranes and in purified reconstituted form

Drug interactions with P-glycoprotein (Pgp) were quantitatively assessed using ATPase assay. Two experimental systems were used, (i) plasma membranes isolated from a multidrug-resistant cell line, which contained 30% Pgp as fraction of total membrane protein, and (ii) purified reconstituted Pgp. The cardioactive drugs verapamil, quinidine, diltiazem, nifedipine, and a series of digitalis analogs, interacted directly with Pgp as shown on ATPase in both systems. Apparent affinities of drug binding were calculated. Direct competition was shown between digitoxin and verapamil. Drug-drug interaction in vivo at the level of Pgp is expected from the results. This approach seems well-suited for empirical determination of drug interactions with Pgp, and prediction of drug-drug interactions.

Pharmacokinetic interactions of moricizine and diltiazem in healthy volunteers

Sixteen healthy male volunteers completed a nonrandomized, sequential, three-phase study. The three phases were 1) moricizine at 250 mg every 8 hours for 7 days with 12 days washout; 2) diltiazem at 60 mg every 8 hours for 7 days; and 3) concomitant administration of moricizine at 250 mg and diltiazem at 60 mg every 8 hours for 7 days. The plasma concentration-time profiles were obtained at the end of each phase for moricizine, diltiazem (with its metabolites desacetyl-diltiazem and N-desmethyl-diltiazem), and both when administered together. Under steady-state conditions, there was a two-way (opposing) pharmacokinetic drug interaction when moricizine and diltiazem were coadministered in healthy volunteers. Both maximum plasma concentration (Cmax) and the area under the plasma concentration-time curve from time 0 to the end of administration (AUC tau) of moricizine increased significantly by 88.9% and 121.1%, respectively. Oral clearance (Clo) decreased by 54%. The terminal half-life (t1/2) of moricizine was not affected, however (2.1 +/- 0.5 hours versus 2.4 +/- 0.7 hours). It is believed that these changes were due to the inhibition of hepatic metabolism by diltiazem, which resulted in an increased systemic availability of moricizine. Moricizine had opposite effects on the pharmacokinetics of diltiazem. Moricizine decreased the Cmax of diltiazem significantly (by 36%) and increased Clo by 52%. A small but statistically significant decrease in the t1/2 from 4.6 +/- 1.3 hours to 3.6 +/- 0.7 hours was observed. Despite this result, no remarkable changes (e.g., in Cmax, AUC, or t1/2) were found for the two major diltiazem metabolites desacetyl-diltiazem and N-desmethyl-diltiazem. It appears that the pharmacokinetic interaction of moricizine and diltiazem was metabolic. With the increase in moricizine concentrations and the decrease in diltiazem concentrations, adjustments in dose may be required to achieve optimal therapeutic response when coadministering both agents.

Safety, tolerability, and pharmacokinetic actions of diltiazem in pediatric liver transplant recipients on cyclosporine

Thirty-two children who had undergone liver transplantation were paired according to their posttransplantation duration, renal function, and diagnoses when possible and randomized either to continue nifedipine (NIF group) or switch to diltiazem (DIL group), in addition to continuing their usual immunosuppressive medications. The cases were followed prospectively regarding diltiazem tolerance, cyclosporine dose requirements, effect on cyclosporine kinetics, diltiazem kinetics, as well as effect on renal function. Diltiazem was well tolerated at a dose of 3 mg to 6.4 mg/kg/day (max 180 mg/day) with infrequent self-limited mild side effects. Cyclosporine daily dose was reduced by a mean of 36.7% and 38.3% at 3 and 6 months, respectively, in the DIL group to achieve target trough cyclosporine levels without modifying liver function. No significant difference in renal function was observed after 3 to 6 months in either group based on blood urea nitrogen and creatinine levels and glomerular filtration rate by the DTPA method. Diltiazem appears to be well tolerated in children and allows for substantial dose reductions of CSA without apparent effects on liver graft function.

Determination of diltiazem and its main metabolites in human plasma by automated solid-phase extraction and high-performance liquid chromatography: a new method overcoming instability of the compounds and interference problems

An automated sample preparation method, based on solid-phase extraction (SPE) was developed on an ASPEC-Gilson device and combined with HPLC for the determination of diltiazem and three of its metabolites in human plasma (N-desacetylmonodesmethyldiltiazem, N-monodesmethyldiltiazem, O-desacetyldiltiazem). A 1-ml volume of plasma is diluted with 0.5 ml of 0.1 M ammonium dihydrogen phosphate and the sample is automatically loaded onto a SPE silica (C18) column (100 mg); the column is flushed with two different solvents, then eluted with 0.5 ml of a 0.1 M ammonium dihydrogen phosphate-acetonitrile mixture (20:80, v/v) containing 0.06% of triethylamine. The eluate is evaporated to dryness and the residue reconstituted with a suitable solvent and injected onto a C8 silica column connected to a UV detector (lambda = 238 nm). This method overcomes problems caused by the partial instability of diltiazem and metabolites in human plasma during analysis. There is no chromatographic interference from endogenous compounds. The limits of quantitation (LOQ) are 2.5 and 2 ng ml-1 for diltiazem and the metabolites in human plasma, respectively. Linearity between concentrations and detector response for diltiazem and metabolites ranged from 10-200 and 5-100 ng ml-1 in human plasma, respectively. The method has been validated.

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.

The effects of chronic oral diltiazem and cimetidine dosing on the pharmacokinetics and negative dromotropic action of intravenous and oral diltiazem in the dog

The kinetics and negative dromotropic action of intravenous (1 mg kg-1) and oral (5 mg kg-1) diltiazem were studied in dogs after acute doses, after treatment for 3 days with oral diltiazem (5 mg kg-1, t.i.d.), and after 3 days' treatment with oral diltiazem (5 mg kg-1 t.i.d.) and cimetidine (200 mg t.i.d.). Plasma concentrations of diltiazem and two of its metabolites, desacetyldiltiazem and desmethyldiltiazem were measured by HPLC. Chronic oral dosing significantly lowered both the systemic and oral clearance of diltiazem, with no changes in either the volume of distribution or blood binding of diltiazem. Cimetidine treatment resulted in a significant reduction in diltiazem oral clearance from chronic control with no effect on its systemic clearance. The AUCs of both metabolites increased by greater than threefold from acute to chronic oral dosing; however, the ratio of each metabolite's AUC to that of diltiazem AUC was not significantly altered. Cimetidine treatment significantly lowered these ratios. The negative dromotropic potency of diltiazem after the acute oral dose was three times greater than that after intravenous or chronic control dosing. Cimetidine treatment resulted in further lowering chronic oral diltiazem potency. These data indicate that the disposition and negative dromotropic action of diltiazem is dependent both on the route of administration and the duration of treatment, and can be altered by co-administration with cimetidine.

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.

Bioavailability of diltiazem as a function of the administered dose

Diltiazem undergoes extensive first-pass metabolism; extrapolation from single to repeated administration thus underestimates plasma concentration values. In order to validate the hypothesis of a partially saturable first-pass effect, four single doses of diltiazem (10, 20, 40, and 120 mg) were administered at weekly intervals to eight healthy volunteers. Results showed that: (a) the inter-subject variability was highest at the lowest dose at the highest dose; (b) bioavailability was almost nil in 3 of 8 of the subjects after the administration of the 10 mg dose; (c) the mean bioavailability increased with the dose from 11.8 +/- 2.5 per cent after 10 mg to 28.2 per cent after 120 mg; (d) the elimination half-life was dose-related; (e) the renal excretion of diltiazem increased with the administered dose from 1.0 +/- 0.3 per cent after 10 mg to 3.0 +/- 0.5 per cent after 120 mg; (f) the greatest amounts of circulating metabolites were present after the lowest doses. These results are consistent with a partially saturable first-pass effect for diltiazem.

Diltiazem pharmacokinetics in elderly volunteers after single and multiple doses

In young healthy volunteers diltiazem does not have linear kinetics between single and multiple doses. Elimination half-life increases and gives AUC's and Cmax higher than those predicted from single dose data. Kinetics of diltiazem were assessed in 16 healthy elderly after a single 60 mg dose and in 24 healthy elderly after 60 mg every 8 h for 7 days. Thirteen participants completed both studies. Elimination half-life, AUC0-24, AUC0-infinity, and Cmax were (mean +/- SE) 7.4 (1.2) h, 349 (34) ng/ml.h, 392 (44) ng/ml.h, and 43 (5) ng/ml respectively after a single dose. After multiple doses elimination half-life, AUC0-48, AUC0-infinity, Cmax and Cmin were respectively 5.7 (0.3) h, 974 (107) ng/ml.h, 1022 (108) ng/ml.h, 102 (7) ng/ml and 43 (5) ng/ml. Exploratory statistics on the 13 volunteers common to both studies showed that the ratio of AUC desacetyl-diltiazem (DAD)/AUC diltiazem rose between single and multiple doses while elimination half-life of both diltiazem and N-desmethyl-diltiazem (MA), tmax, and AUC MA/AUC diltiazem were not affected. The conclusion of this study is that elimination half-life of diltiazem does not increase in elderly between single and multiple doses, possibly due to an increased biotransformation into DAD.

Effects of calcium channel blockers on the development of early rat postimplantation embryos in culture

Rat embryos (9.5-day-old) were cultured for 48 h in the presence of nifedipine (NIF), nimodipine (NIM), nitrendipine (NIT), gallopamil HCl (GAL), verapamil HCl (VER) and diltiazem HCl (DIL). The effects on growth and morphogenetic differentiation in vitro were monitored. Dose-response relationships were evaluated, including an assessment of the "no-observed-effect-level" (NOEL) or the "lowest-observed-effect-level" (LOEL), and the lowest concentration tested inducing abnormalities in 100% of the embryos ("100% EL"). The morphological alterations observed at the highest concentrations were very similar for all six drugs. The abnormalities concerned yolk sac circulation and morphology, as well as heartbeat, the morphology of the heart, head, neural tube, or forelimbs, and the shape of the embryo. The abnormal embryos were also growth retarded (decrease in protein content and crown-rump length). Interference with calcium channel functions seems to represent an interesting model for studying a special kind of abnormal prenatal development, especially the differentiation of certain mesenchymal structures. The concentration ranges between NOELs and 100% ELs were found to be: NIM = 0.1-1 microgram/ml; NIT and VER = 1-10 micrograms/ml; DIL = 1-30 micrograms/ml, and LOELs-100% ELs were: GAL = 1-10 micrograms/ml; NIF = 10-30 micrograms/ml.

Inhibition of apolipoprotein B net synthesis and secretion from cultured rat hepatocytes by the calcium-channel blocker diltiazem

1. The effect of the Ca2+-channel blocker diltiazem on hepatic apolipoprotein B (apo B) synthesis and secretion was studied in 12-18 h cultures of collagenase-dispersed rat hepatocytes. 2. The presence of diltiazem in the medium decreased apo B secretion by hepatocytes in a concentration-dependent manner. At 25 microM, diltiazem inhibited apo B secretion by approx. 36%, but there was no evidence of intracellular accumulation of apo B. 3. The inhibition of apo B secretion by hepatocytes was significantly correlated with cell-associated diltiazem (r = 0.72, P less than 0.01). 4. The rate of apo B secretion remained linear over 16 h even in the presence of 50 microM-diltiazem. 5. At diltiazem concentrations in the medium which were inhibitory for apo B secretion, [14C]acetate incorporation into cellular lipids and [35S]methionine incorporation into protein were enhanced. 6. Diltiazem inhibited the secretion of the apo B variants with a preferential inhibition of the higher-molecular-mass form of apo B (apo BH) over the lower-molecular-mass form (apo BL) at diltiazem concentrations in the medium greater than 25 microM. 7. Together, these results suggest that Ca2+ may play an important role in the synthesis and secretion of apo B-containing lipoproteins.

Effects of cardiovascular disease on pharmacokinetics

The pathophysiologic changes occurring in cardiovascular disease can affect the kinetics of drugs in several different ways. The present review examines these modifications and the underlying mechanisms. The kinetics of specific agents, such as antiarrhythmic, antihypertensive, cardiotonic, and other drugs are considered, and the clinical implications are outlined. The clinician should be aware of these modifications, because they require an adjustment of the dosage regimen. A rational basis for a correct therapeutic choice can be provided by adequate knowledge of these modifications.

The effects of encainide versus diltiazem on the oxidative metabolic pathways of antipyrine

The effects of diltiazem and encainide on the pharmacokinetics and metabolism of antipyrine were compared in nine healthy male volunteers. Diltiazem 90 mg every 8 hours for 5 days decreased the oral clearance of antipyrine from 2.34 to 1.86 L/hour (p less than 0.05) and increased half-life from 12.7 to 15.9 hours (p less than 0.05). Diltiazem reduced the formation rate constants for 3-hydroxymethylantipyrine by 27% (p less than 0.05) and 4-hydroxyantipyrine by 37% (p less than 0.05). There was also a 21% reduction in the formation rate constant for norantipyrine (0.05 less than p less than 0.10). Encainide 25 mg every 8 hours for 5 days had no apparent effect on the oral clearance or half-life of antipyrine, or on the formation rate constants for metabolites of antipyrine. In contrast to a previously published report in rats, encainide, unlike diltiazem, does not inhibit the oxidative metabolism of antipyrine in humans.