Pharmacokinetics of slow-release diltiazem and its effect on atrioventricular conduction in healthy volunteers

Convolution- and Deconvolution-Based Approaches for Prediction of Pharmacokinetic Parameters of Diltiazem Extended-Release Products in Flow-Through Cell Dissolution Tester

The present study evaluated the effect of different configuration setups of the Flow-Through Cell (USP IV) dissolution tester in developing in vitro-in vivo correlation (IVIVC). A Biopharmaceutics Classification System (BCS) Class I Diltiazem (DTZ), formulated in extended-release (ER) gel-matrix system, was employed for this purpose. The study also assessed the validity and predictability of IVIVC employing both deconvolution- and convolution-based approaches. In vitro release was conducted in USP IV as open- or closed-loop setups, while the pharmacokinetic (PK) data were obtained from a previous fasted-state cross-over study conducted on 8 healthy male volunteers, after oral administration of ER matrix tablets against market product (Tildiem Retard® 90 mg). PK parameters (C_max, AUC_0-t and AUC_0-∞) were predicted, and compared with actual data to establish the strength of correlation models. Results showed that DTZ release from ER products was influenced by operating the FTC in different configuration-setups, where ≥ 75% of labeled DTZ was released after 6 h and 12 h using the open- and closed-loop settings, respectively. Correlation between fraction-dissolved versus fraction-absorbed for both ER products displayed linear relation upon employing FTC open-loop setup. Convolution-based approach was more discriminative in predicting DTZ in vivo PK parameters with a minimal prediction error, compared to deconvolution-based approach. A successful trial to predict DTZ PKs from individual in vitro data performed in USP IV dissolution model was established, employing convolution technique. Basic principle of the convolution approach provides a simple and practical method for developing IVIVC, hence could be utilized for other BCS Class I extended-release drug products.

A pharmacological characterization of electrocardiogram PR and QRS intervals in conscious telemetered rats

INTRODUCTION

The conscious telemetered rat is widely used as an early in vivo screening model for assessing the cardiovascular safety of novel pharmacological agents. The current study aimed to identify its utility in assessing electrocardiogram (ECG) PR and QRS interval changes.

METHOD

Male Han-Wistar rats (~250 g) were implanted with radio-telemetry devices for the recording of ECG and haemodynamic parameters. Animals (n = 4-8) were treated with single doses of calcium (nifedipine, diltiazem or verapamil; CCBs) or sodium channel blockers (quinidine or flecainide; SCBs) or their corresponding vehicles in an ascending dose design. Data was recorded continuously up to 24 h post-dose. Pharmacokinetic analysis of blood samples was performed to allow comparison of effects to published data in other species.

RESULTS

Of the CCBs, only diltiazem (300 mg/kg) prolonged the PR interval (49 ± 2 versus vehicle: 43 ± 1 ms), although this was not statistically significant (p = .11). QA interval decreased with nifedipine (30 ± 1 versus 24 ± 0 ms) and diltiazem (34 ± 1 versus 27 ± 1 ms) but increased with verapamil (30 ± 0 versus 37 ± 1 ms) demonstrating pharmacological activity of each agent. Both SCBs, caused statistically significant (p < .05) increases in both intervals - quinidine (100 mg/kg; PR: 50 ± 2 versus 43 ± 1 ms; QRS: 22 ± 2 versus 18 ± 1 ms) and flecainide (9 mg/kg; PR: 56 ± 1 versus 46 ± 1 ms; QRS: 27 ± 1 versus 21 ± 1 ms). Drug plasma exposure was confirmed in all animals.

DISCUSSION

At similar plasma concentrations to other species, the conscious telemetered rat demonstrates limited utility in assessing PR interval prolongation by CCBs, despite significant contractility effects being observed. However, results with SCBs demonstrate a potential application for evaluating drug-induced QRS prolongation.

Stability and bioavailability of diltiazem/polyethylene oxide matrix tablets

The aim of this study was to prepare and evaluate in vitro and in vivo; Diltiazem-Hydrochloride (DTZ) in sustained-release matrix tablets. Stability of DTZ tablets prepared with polyethylene oxide (MWs 900 000, 4 000 000, and 8 000 000) with or without addition of electrolytes was carried-out for 1-month, under short-term storage at 40 °C/75% RH. Stability was evaluated by DTZ content, DSC and drug release using the Flow-Through Cell (USP # IV). The majority of stored tablets were stable for 1-month under short-term storage with respect to DTZ content and drug release. DSC curves of stored samples showed appearance of new exothermic peak after 1-month storage at 40 °C/75% RH, which was not observed after 5 years storage at room temperature. A selected formula was tested in vivo against reference product on eight healthy human volunteers. DTZ-plasma profiles were different between the two formulae. However, no statistically significant differences were detected between C_max, AUC_0-48 and AUC_0-∞. The two products were therapeutically in-equivalent, as 90% confidence intervals "T/R" were 88.82-205.76, 91.40-139.94, and 93.73-134.97 for C_max, AUC_0-48 and AUC_0-∞, respectively. This study highlighted possible differences observed between the two regimes frequently applied for stability testing.

Sustained-release diltiazem reduces myocardial ischemic episodes in end-stage renal disease: a double-blind, randomized, crossover, placebo-controlled trial

End-stage renal disease (ESRD) patients receiving maintenance hemodialysis and suffering from coronary artery disease (CAD) often receive doses of calcium channel antagonists that are too low. This may be the result of physician's desire to avoid adverse side effects during hemodialysis. The aim of this study was the assessment of the safety and efficacy of incremental doses of diltiazem for the treatment of myocardial ischemia in ERSD patients with CAD to identify the optimal dose of the drug. A total of 196 chronic hemodialysis patients were enrolled with CAD showing more than 5 min of transient myocardial ischemia during a 48-h Holter ECG monitoring. A double-blind, randomized, crossover, placebo-controlled trial design was used. Incremental doses of diltiazem (120 to 240 mg/d) were administered in 4 mo. With a dose of 120 and 180 mg/d, a significant reduction in the number and duration of total and symptomatic ischemic episodes was observed (P < 0.001), but the number and the duration of silent ischemic episodes were not reduced. Conversely, the efficacy on silent myocardial ischemia was obtained with a dosage of diltiazem of 240 mg/d (P < 0.001). In addition, with a sustained-release formulation (120 mg twice daily), the efficacy was similar to that obtained with four 60-mg tablets, but the safety was improved, especially during hemodialytic session. The circadian variations analysis of transient ischemic episodes showed a significant reduction in both ischemic peaks observed at baseline only with 240 mg/d of diltiazem. The findings emphasize that sustained-release diltiazem (120 mg twice daily) can be largely useful in uremic patients with CAD on maintenance dialysis. Diltiazem reduces the number and the duration of silent ischemic episodes, has a good tolerability, and positively modifies the circadian pattern of ischemic episodes.

Preparation of casein-chitosan microspheres containing diltiazem hydrochloride by an aqueous coacervation technique

Sustained release casein-chitosan microspheres containing diltiazem hydrochloride (DTZ) were prepared with colloidal coacervation technique in a completely aqueous environment. The interaction between chitosan solution in dilute acetic acid (5% v/v) and casein solution in 0.5 M sodium hydroxide was the basis for the microspheres formation. Formaldehyde was used for the surface hardening of the droplets by cross-linking and thus fixing the shape and surface morphology of the formed microspheres. The entrapment efficiencies of the microspheres were variables (14.5-53.7%) depending on the preparation conditions. The prepared microspheres exhibited an angle of repose values between 31.9-42.0 degrees indicating good free flowing nature, whereas DTZ powder as such was non-flowable. The dissolution profiles of DTZ from casein-chitosan microspheres showed retarded release pattern of the drug into distilled water. Casein and chitosan concentrations, initial drug concentration and stirring time were found to be the main parameters that affect the properties and the performance of the prepared microspheres. The retarded release of DTZ was increased by increasing casein concentration, and stirring time. On the other hand, increasing chitosan concentration and using high initial drug loading showed a fast drug release.

Preparation and in vitro dissolution profile of dual polymer (Eudragit RS100 and RL100) microparticles of diltiazem hydrochloride

A microparticulate dosage form for a highly soluble drug, diltiazem hydrochloride, was formulated with Eudragit RS100 and RL100 using a novel dual polymer technique. A mixture of diltiazem with Eudragit RS100 (low water permeability) in acetone was coacervated into soft polymer microdrops, following which a mixture of diltiazem and RL100 (high water permeability) was added to produce microparticles consisting of both polymers with diltiazem dispersed in the matrix. A second formulation was developed using the same method except using Eudragit RS100 for both steps. For a comparative study, diltiazem, Eudragit RS100 and RL100 were combined together in a single matrix and formulated into microparticles. In vitro drug release profiles using USP paddle dissolution apparatus 2 revealed that dual polymer matrix microparticles containing Eudragit RS100 in the inner and Eudragit RL100 in the outer core exhibit a suitable release profile with an initial release of the drug followed by a plateau level for the test period of 5 h. Differential scanning calorimetric analysis showed no interaction of the drug with the polymers.

Endothelin and calcium antagonists in the skin microcirculation of patients with coronary artery disease

BACKGROUND

Endothelin, a potent endothelium-derived vasoconstrictor peptide, is elevated in coronary artery disease (CAD); however, its pathophysiological role is uncertain. Calcium antagonists are widely used in patients with CAD. Using laser Doppler flowmetry, we investigated the influence of two endothelin antagonists and the calcium antagonist diltiazem on endogenous and exogenous endothelin in the skin microcirculation of CAD patients and healthy control subjects.

METHODS AND RESULTS

Both endothelin antagonists and diltiazem applied intradermally induced vasodilation in CAD patients, which was more pronounced with the ETA/ETB antagonist than with the ETA antagonist or diltiazem. Exogenous endothelin led to profound vasoconstriction in CAD patients and healthy volunteers. Both endothelin antagonists and diltiazem blunted the vasoconstriction to exogenous endothelin in CAD patients and young healthy volunteers and less so in old healthy volunteers. However, compared with both endothelin antagonists, a 10-times-higher dose of diltiazem was required. Systemic diltiazem (240 mg, slow release) attenuated endothelin-induced vasoconstriction in CAD patients. Neurogenic vasodilation to exogenous endothelin was inhibited by both endothelin antagonists.

CONCLUSIONS

This study demonstrates that endogenous endothelin of CAD patients contributes to the regulation of vascular tone in the skin microcirculation not only through ETA receptors but also possibly through ETB receptors. Diltiazem inhibited endothelin-induced vasoconstriction, but endothelin antagonists were slightly more effective. Thus, endothelin antagonists represent potent new tools to interfere with the vascular effects of endothelin in CAD patients. Future studies must confirm these findings in other areas of the circulation.

Pharmacokinetics and pharmacodynamics of a slow-release formulation of diltiazem after the administration of a single and repeated doses to healthy volunteers

Diltiazem is a calcium antagonist used in angina pectoris and hypertension. There is little information concerning the slow-release (SR) formulation in the literature. The pharmacokinetics of diltiazem SR (120 mg) have been assessed over a 36h period in healthy volunteers after single- (SD) and multiple-dose (MD) administrations. Cmax, AUC0-36, and AUC0-infinity were significantly increased at steady state compared to the extrapolated SD values, suggesting accumulation of the drug. Renal and cardiovascular parameters have also been assessed at intervals of 3-6h during baseline (B) and following single and multiple doses of diltiazem SR. Diuresis over a 24 h period was increased, but not significantly, by the administration of diltiazem SR i.e. 1782 ml (MD) and 1915 ml (SD), versus 1626 ml (B). Natriuresis and creatinine clearance were slightly decreased by diltiazem SR, compared to B values; this might be due to the relatively short period over which steady state was maintained (five days) and the effects of norepinephrine and angiotensine II on renal vasculature and the pharmacokinetics of diltiazem SR. No increase in the systolic blood pressure occurred after the administration of diltiazem SR; diastolic blood pressure and PR interval were decreased and increased respectively by diltiazem SR. These results do not appear to be clinically significant. Finally, no relation was found between the pharmacokinetics and pharmacodynamics of diltiazem. This may be attributed to the absence of clinically significant effects in healthy volunteers, the presence of active metabolites, the pharmacokinetics of the SR formulation and/or the accumulation of the drug at steady state.

Comparative pharmacokinetics and pharmacodynamics of two marketed bid formulations of diltiazem in healthy volunteers

Cardizem SR and Bi-Tildiem were both approved in their respective countries on the basis of clinical trials demonstrating efficacy and safety in the treatment of angina pectoris. In this cross-over randomized study, we assessed whether these two sustained-release formulations of diltiazem have equivalent pharmacokinetic and pharmacodynamic profiles. Twenty-four young healthy male volunteers were hooked to Holters and ambulatory blood pressure monitors for 24 h to establish baseline systolic blood pressure (SBP), diastolic blood pressure (DBP), sinus rate and PR intervals. They then received a single dose of 120 mg of diltiazem from one formulation. The pharmacodynamic measurements were recorded for a further 24 h and blood samples were collected over 36 h for evaluation of diltiazem in plasma by a high-performance liquid chromatogrpahic (HPLC) method. The procedures were repeated with the alternate formulation after a 7 d wash-out. Pharmacokinetics showed statistically significant (p < 0.01) differences in AUC0-12 with means (+/- SD) of 519.2(+/- 172.8) and 429.6(+/- 147.2) ng h ml-1, AUC0-36 of 835.6(+/- 281.6) and 730.9 (+/- 271.5) ng h ml-1 and Cmax of 89.1(+/- 30.3) and 61.1(+/- 21.2) ng ml-1 for Cardizem SR and Bi-Tildiem, respectively. The only pharmacodynamic parameter showing a statistically significant difference in change from baseline between the two formulations was DBP with mean (+/- SD) change in AUC0-12 of -13.6(+/- 20.8) and +8.4(+/- 31.7) mm Hg h (p = 0.0135) and in AUC0-24 of -33.0(+/- 43.7) and -0.3(+/- 59.2) mm Hg h (p = 0.0463) for Cardizem SR and Bi-Tildiem, respectively. These findings suggest that assessment of efficacy of sustained-release formulations of diltiazem by bioequivalence could be misleading. They also confirm that a single dose of diltiazem does not elicit a significant pharmacodynamic response in healthy volunteers. Equivalence for such formulations should therefore be demonstrated by pharmacodynamic evaluation or clinical studies in a patient population.

In vitro/in vivo correlation of prolonged release dosage forms containing diltiazem HCI

Six preparations were considered: three multiple unit dosage forms (micropellets in capsules) (D, E and G) and one matrix tablet (B) were experimental prolonged release formulations, two non-disintegrating tablets (A and C) were commercial products. The in vitro dissolution behaviour of the differing formulations was investigated using the USP XXII paddle apparatus. The in vivo study was effected on a panel of 12 healthy volunteers. The two commercial tablets (A and C) showed mean dissolution time (MDT) of 1.34 and 1.44 h and td of 91 and 92 min, respectively; for prolonged release formulations (B, E, D, and G) MDT ranged between 2.28 and 4.23 h and td between 149 and 291 min. The mean residence time (MRT) was 8.68 and 6.47 h for tablets A and C, respectively; it ranged between 9.62 and 10.24 h for the multiple unit formulations E, D, and G and was 11.27 h for matrix B. Formulation B also showed the higher apparent elimination half-life t1/2 (7.12 h), while apparent t1/2 for all the other formulations were very similar, ranging between 5.04 and 5.28 h. High variability between the various formulations was found for Cmax and AUC values, and no relationships could be established with the type of formulation. An in vitro/in vivo correlation was found for all the formulations examined on the basis of analogous parameters (MDT and MRT); (r = 0.83, p < 0.05). In a few cases the Wagner-Nelson deconvolution method was applied to individual plasma level versus time curves and the corresponding absorption curves were obtained. In these cases the in vitro/in vivo correlation was tested on the basis of the comparison of the in vivo absorption curves with the in vitro dissolution profiles. This was accomplished using the 'Levy's plot' (per cent released versus per cent absorbed) approach and provided further support for the correlation found.

Lack of effect of isradipine on cyclosporin pharmacokinetics

The influence of isradipine as a long acting form (IcazR LP 5 mg) on cyclosporin pharmacokinetics was studied in six hypertensive renal transplant patients (mean age 37 yrs; mean body weight 62 kg). These patients received a mean daily cyclosporin dose of 307 mg in two equal intakes. Isradipine was orally administered once a day at a dose of 5 mg before the morning cyclosporin intake. Cyclosporin kinetics was assessed over a 0-12-h period, the day before (D-1) and 13 days (D+13) after isradipine treatment. Whole blood concentrations of cyclosporin were determined by radioimmunoassay (RIA) using the SandimmuneR-RIA kit (specific and non-specific monoclonal antibodies). Area under the blood concentration-time curve (AUC), the maximum blood concentration (Cmax) and the time to reach Cmax (Tmax) on D-1 and D+13 were not significantly different whatever the specificity of the RIA method. For example, the mean AUC +/- sd values were 5,247 +/- 2,255 (D-1) vs 5,317 +/- 1,675 (D+13) microgram.1(-1).h for the specific and 20,905 +/- 8,317 vs 19,327 +/- 5,758 microgram.1(-1).h for the non-specific determinations. Therefore, the pharmacokinetics of cyclosporin is not influenced by co-administration of isradipine at a therapeutic dosage. Moreover, the clinical results show that isradipine treatment was effective after 13 days administration (mean systolic blood pressure 132 vs 158 mm Hg, P < 0.05 and mean diastolic blood pressure 77 vs 93 mm Hg, P < 0.05 in supine position), and well tolerated throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules

The influence of food on the bioavailability of a conventional tablet and of a slow-release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 x 30 mg, first group) or as a slow-release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazem, and deacetyldiltiazem were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC infinity) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC infinity of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow-release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.