Bioavailability of diltiazem as a function of the administered dose

Comparison of various calcium antagonist on vasospastic angina: a systematic review

BACKGROUND

Coronary artery vasospasm is an abnormal spasm of coronary arteries that cause transient or complete occlusion without exertion. It causes stable angina to ACS. However, this can be prevented by calcium channel blockers (CCBs) which suppress Ca²⁺ influx into the vascular muscle cells. Nevertheless, several CCBs adverse effects are harmful for these patients. Selecting the right CCBs would give the best clinical practice.

METHOD

The studies were obtained from four major medical databases by various keywords. Inclusion and exclusion criteria were implemented as adult >18 years, observational study, English language and drug of interest. Duplicates were eliminated, and the remaining studies were reviewed. Final full-texts assessment was conducted independently by Newcastle-Ottawa Scale and Revised Cochrane.

RESULTS

The search found 1378 articles. However, six studies were selected after implementing the study criteria. Diltiazem was found to decrease angina and increase quality of life until 12th week of treatment; however, some adverse effects include atrioventricular block and recurrent angina up till 4th week were found. Meanwhile, nifedipine was found to decrease vasospastic angina (VSA) by the fourth and eighth weeks of treatment. Nevertheless, it caused excessive drop in BP and increase heart rate by eighth week. In addition, slow-release preparation of both CCBs were found to increase efficacy and compliance. Lastly amlodipine was also found to decrease VSA by 17%±140% and 33% after 6 weeks, but further studies needed.

CONCLUSION

Diltiazem, nifedipine and amlodipine are potent in decreasing VSA, however, tailoring specific CCBs adverse reactions to patient condition and the drug preparation would be substantially beneficial for the outcome.

Fabrication of a sensitive sensor for electrochemical detection of diltiazem in presence of methyldopa

Diltiazem (DTZ) is one of the most important drugs in blood pressure that is used to treat cardiovascular diseases. With this overuse of this drug and its use for suicide, swelling and neck cramps and fever has made it important to measure it. So, this paper will give an account of modification of carbon paste electrode with the ternary-nanocomposite including reduced-graphene oxide (rGO), cadmium oxide and 1-ethyl 3- methyl imidazole chloride as ionic liquid for using the determination of DTZ in blood serum samples. Characterization of the synthesized rGO, cadmium oxide, and modified electrodes and their electrochemical performance were studied by, scanning electron microscopy, and X-ray diffraction, electrochemical impedance spectroscopy, and voltammetry technique. The improvement of the DTZ oxidation current by modified electrode originated from the increased electrode surface area. The optimized method was validated and the results showed that LOD = 3 nM and good linearity. Also, a linear concentration range of 0.01-150 μM with a LOD of 0.03 μM in presence methyldopa were achieved based on the electrochemical investigations. The prepared sensor showed good repeatability (RSD = 2.26%) and selectivity for DTZ determination in the real samples (relative recovery of 93-102%).

Comparing Various In Vitro Prediction Methods to Assess the Potential of a Drug to Inhibit P-glycoprotein (P-gp) Transporter In Vivo

The evaluation of potential of a new molecular entity (NME) to inhibit P-glycoprotein (P-gp) in vivo is an integral part of drug development and is recommended by regulatory agencies. In this study, we compared the performance of 5 prediction methods and their associated criteria (including those from the European Medicines Agency, the US Food and Drug Administration, and the Pharmaceuticals and Medical Devices Agency of Japan) for assessing the potential of an NME to inhibit P-gp in vivo based on in vitro assessment. We collected in vitro (eg, half-maximal inhibitory concentration [IC₅₀ ], fraction unbound to plasma protein) and in vivo (eg, dose, maximum concentration, change in maximum concentration or area under the plasma concentration-time curve of the substrate digoxin) data for 50 Food and Drug Administration-approved, orally administered drug products containing 53 NMEs, from the University of Washington Metabolism and Transport Drug Interaction Database, Drugs@FDA, and PubMed. All methods yielded similar accuracy with small differences in false-negative (FN) and false-positive (FP) predictions. In addition, use of ratio of the theoretical maximum gastrointestinal concentration to IC₅₀ is sufficient for a reasonable prediction for these orally administered drugs as potential P-gp inhibitors based on our dataset. The FN and FP rates varied depending on the cut-off value for the ratio of the theoretical maximum gastrointestinal concentration/IC₅₀ . Possible reasons underlying FP and FN results from different methods should be taken into consideration to predict in vivo P-gp inhibition.

Semiphysiologically based pharmacokinetic models for the inhibition of midazolam clearance by diltiazem and its major metabolite

Prediction of the extent and time course of drug-drug interactions (DDIs) between the mechanism-based inhibitor diltiazem (DTZ) and the CYP3A4 substrate midazolam (MDZ) is confounded by time- and concentration-dependent clearance of the inhibitor. Semiphysiologically based pharmacokinetic (PBPK) models were developed for DTZ and MDZ with the major metabolite of DTZ, N-desmethyldiltiazem (nd-DTZ), incorporated in the DTZ model. Enzyme kinetic parameters (k(inact) and K(I)) for DTZ and nd-DTZ were estimated in vitro and used to model the time course of changes in the amount of CYP3A4 in the liver and gut wall, which in turn, determined the nonlinear elimination of MDZ and DTZ, and the corresponding DDI. The robustness of the model prediction was assessed by comparing the results of the prediction to published DTZ pharmacokinetic and DTZ/MDZ interaction data. A clinical study was conducted to further validate the predicted increase of MDZ exposure after DTZ treatment. The model predicted the nonlinear disposition of DTZ after single and multiple oral doses. The clinical study showed that DTZ treatment resulted in 4.1- and 1.6-fold increases in MDZ exposure after oral and intravenous MDZ administration, respectively, suggesting that the DDI in the gut wall plays an important role in the DTZ/MDZ interaction. The semi-PBPK model incorporating the DDI at the gut wall, and the effect of nd-DTZ successfully predicted the nonlinear disposition of DTZ and its interaction with MDZ. Moreover, model simulation suggested that both DTZ and nd-DTZ contributed to the overall inhibitory effect after DTZ administration, and the values of the in vitro estimated inhibition parameters and CYP3A4 turnover rate are critical for the prediction.

The influence of cimetidine on the pharmacokinetics of diltiazem and its main metabolite in rabbits

The purpose of this study was to investigate the pharmacokinetic alteration of diltiazem and its main metabolite, deacetyldiltiazem, after oral administration of diltiazem in rabbits with or without cimetidine co-administration. The area under the plasma concentration-time curve (AUC) of diltiazem was significantly elevated in rabbits pretreated with cimetidine, suggesting that the oral clearance, an index of intrinsic clearance, may be decreased by the cimetidine treatment. Consistent with the increased AUC by the treatment, peak plasma concentration (Cmax) for diltiazem was also elevated. Apparent volume of distribution normalized by the bioavailability (Vd/F) of diltiazem increased significantly in rabbits pretreated with cimetidine increased. Taken together with the fact that the first pass metabolism for diltiazem is the primary determinant for the oral bioavailability, these observations indicate that increases in the oral clearance and Vd/F may be a manifestation of the decreased first pass metabolism. Consistent with the hypothesis, the AUC of deacetyldiltiazem was significantly decreased in rabbits with cimetidine treatment. Ratio of deacetyldiltiazem to total diltiazem in the plasma was significantly decreased in rabbits with cimetidine treatment. These observations suggested that the metabolism of diltiazem to deacetyldiltiazem was reduced by cimetidine treatment and that the dosage of diltiazem should be adjusted when the drug is co-administered chronically with cimetidine in a clinical setting.

Absorption and Metabolic Extraction of Diltiazem from the Perfused Rat Small Intestine

The metabolic extraction of diltiazem was examined in conjunction with its absorption, using rat small intestine perfused in situ by the single-pass method, to clarify its intestinal metabolism. This is a topic of increasing interest which has not been fully clarified, particularly as far as the extent of metabolic extraction and the enzymes involved (cytochrome P450 (CYP) 3A and/or others) are concerned. The intestinal availability (Fi) of diltiazem was evaluated at steady-state by dividing the fraction absorbed into the mesenteric venous blood (Fa,b) by the fraction that disappeared from the intestinal lumen (Fa). The Fi of diltiazem (0.05 mM) was 0.126 and, hence, the extraction ratio (Ei=1-Fi) was 0.874, indicating that diltiazem undergoes extensive first-pass metabolism during its passage through the intestinal mucosa. The Ei was unchanged when the concentration was increased to 0.5 mM, suggesting that metabolism is linear over this concentration range. Thereafter, Ei decreased with concentration, demonstrating saturable metabolism, and reached an insignificant level at the highest concentrations of 30 and 50 mM. The decrease in Ei, or increase in Fi, was brought about by an increase in Fa,b (from about 0.02 to about 0.05) in the concentration range up to 10 mM and by a decrease in Fa (from about 0.15 to about 0.05) at concentrations higher than that. These results suggest that the extraction observed at the lower concentrations is almost solely attributable to metabolic extraction of a saturable nature. However, ketoconazole and cyclosporin A, which are specific CYP3A inhibitors, inhibited the metabolic extraction of diltiazem (0.05 mM) by only about 20% at the concentration (40 microM) at which they inhibited CYP3A almost completely, suggesting that the contribution of CYP3A to intestinal diltiazem metabolism is not marked. Thus, the present study demonstrates that diltiazem undergoes extensive first-pass metabolism in the rat small intestine, although the contribution of CYP3A seems to be relatively minor.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Comparative bioavailability of diltiazem in prolonged-release oral preparations

This study was conducted to compare the bioavailability of two prolonged-release pharmaceutical forms containing 300 mg of diltiazem. The test formulation is a new design of tablets with a hydrophilic matrix, and the reference formulation is capsules containing prolonged liberation microgranules, in the same dose, that are commercially available in the pharmaceutical market. Diltiazem plasma concentrations were analyzed by high-performance liquid chromatography (HPLC), which involves solid-phase extraction for plasma sample preparation. Twelve healthy volunteers participated in the study, which had a single-dose, two-treatment, two-sequence-crossover, randomized design. The preparations were compared using pharmacokinetic parameters such as the area under the plasma concentration-time curve AUC(0-36), peak plasma concentration Cmax, and Cmax/AUC(0-36) ratio as a measure for the absorption rate. No statistically significant difference was observed for any of the parameters, and the 90% confidence intervals calculated for the ratio of the logarithmically transformed AUC(0-36) and Cmax/AUC(0-36) values of both formulations were within the bioequivalence limit of 0.80-1.25. Moreover, an in vitro study of dissolution according to USP 23 was conducted, and the in vitro parameters were calculated.

Pharmacokinetics of diltiazem and its major metabolite, deacetyidiltiazem after oral administration of diltiazem in mild and medium folate-induced renal failure rabbits

The pharmacokinetic changes of diltiazem (DTZ) and its main metabolite, deacetyldiltiazem (DAD) were studied after oral administration of DTZ to normal rabbits and mild and medium folate-induced renal failure rabbits. DTZ 10 mg/kg was given to the rabbits either orally (n=6). Plasma concentrations of DTZ and DAD were determined by a high performance liquid chromatography assay. The area under the plasma concentration-time curves (AUC) and maximum plasma concentration (Cmax) of DTZ were significantly increased in mild and medium folate-induced renal failure rabbits. The metabolite ratio of the DTZ to DAD were significantly decreased in mild and medium folate-induced renal failure rabbits. The volume of distribution (Vd) and total body clearance (CLt) of DTZ were significantly decreased in mild and medium folate-induced renal failure rabbits. The elimination rate constant (beta) of DTZ was significantly decreased in folate-induced renal failure rabbits, but that of DAD was significantly increased. These findings suggest that the hepatic metabolism of DTZ was inhibited and the Vd, CLt and beta of DTZ were significantly decreased in mild and medium folate-induced renal failure rabbits.

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.

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.

Pharmacokinetics of alfuzosin after single oral administration to healthy volunteers, of three different doses

The aim of this study was to assess the linearity of pharmacokinetic of alfuzosin, administered by oral route, at the doses of 1, 2.5, and 5 mg to 12 young healthy volunteers. The pharmacokinetic parameters (tmax, Cmax, AUC, t1/2 beta) obtained from plasma alfuzosin concentrations after administration of the three doses show that pharmacokinetics of alfuzosin is linear in the range of doses 1-5 mg. Mean pharmacokinetic parameters of alfuzosin observed after 1, 2.5, and 5 mg were, respectively: tmax (h) 1.5 +/- 0.3, 1.1 +/- 0.2, 1.3 +/- 0.1; Cmax (ng ml-1) 2.6 +/- 0.3, 9.4 +/- 1.2, 13.5 +/- 1.0; AUC (ng ml-1 h) 17.7 +/- 2.9, 51.7 +/- 7.1, 99.0 +/- 14.1; t1/2 (h) 3.7 +/- 0.4, 3.9 +/- 0.2, 3.8 +/- 0.3. Cmax (corrected by the dose) obtained after 2.5 mg was significantly higher than those obtained after 1 and 5 mg. This difference seems to be due principally to the intraindividual variability. The absence of statistically significant difference on individual values of AUC corrected by the administered dose, supports the linearity of the pharmacokinetics of alfuzosin in the range of doses between 1 and 5 mg. Some postural hypotension, clinical criterion, was observed with a frequency increasing with the dose in these healthy subjects: 0 volunteers of 12 after 1 mg, 3 volunteers of 12 after 2.5 mg and 4 volunteers of 12 after 5 mg.