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 (Cmax, AUC0-t and AUC0-∞) 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.

Dose tailoring of tacrolimus based on a non-linear pharmacokinetic model in children with refractory nephrotic syndrome.

The population pharmacokinetics (PPK) of tacrolimus (TAC) in children with refractory nephrotic syndrome (RNS) have not been well-characterized. This study aimed to investigate the significant factors affecting the TAC PPK characteristics of children with RNS and to optimize the dosing regimen. A total of 494 concentrations from 108 children were obtained from routine therapeutic drug monitoring between 2016 and 2018. Information regarding the demographic features, laboratory test results, genetic polymorphisms of CYP3A5 (rs776746) and co-therapy medications were collected. PPK analysis was performed using the nonlinear mixed-effects modelling (NONMEM) software and two modelling strategies (the linear one-compartment model and nonlinear Michaelis-Menten model) were evaluated and compared. CYP3A5 genotype, weight, daily dose of TAC and daily dose of diltiazem were retained in the final linear model. The absorption rate constant (Ka) was set at 4.48 h-1 in the linear model, and the apparent clearance (CL/F) and volume of distribution (V/F) in the final linear model were 14.2 L/h and 172 L, respectively. CYP3A5 genotype, weight and daily dose of diltiazem were the significant factors retained in the final nonlinear model. The maximal dose rate (Vmax) and the average steady-state concentration at half-Vmax (Km) in the final nonlinear model were 2.15 mg/day and 0.845 ng/ml, respectively. The nonlinear model described the pharmacokinetic data of TAC better than the linear model in children with RNS. A dosing regimen was proposed based on weight, CYP3A5 genotype and daily dose of diltiazem according to the final nonlinear PK model, which may facilitate individualized drug therapy with TAC.

Modulation of Drug Release from Natural Polymer Matrices by Response Surface Methodology: in vitro and in vivo Evaluation.

PURPOSE: The present work aimed at challenging the efficacy of natural gums, karaya and locust bean gum, as matrix-forming polymers for the formulation of sustained-release tablets of diltiazem, a model drug. METHODS: Central design composite was adopted for the formulation and optimization of tablet formulations. The two gums have been selected as independent variables. The dependent factors chosen were the amount of drug released in 1st hour (Y1), amount of drug released after 12 h (Y2), diffusion exponent (Y3), and time for half of the total drug released (T50%) (Y4). Wet granulation approach was used for the formulation of tablets. FT-IR, DSC, in vitro dissolution, swelling-erosion investigations, SEM, and stability studies were carried out. RESULTS AND DISCUSSION: It was evident that the release pattern from the prepared formulations was significantly influenced by the quantity of gum(s) in the tablet. FT-IR and DSC results confirm drug-polymer compatibility. Polynomial equations were used for the prediction of quantitative impact of independent factors at different levels on response variables. After ANOVA analysis, the significant factors were considered for constrained optimization to get the optimized formula. The optimized formula generated by the response surface methodology was evaluated both for in vitro and in vivo properties. The optimized formula and a sustained-release marketed product were subjected to in vivo studies in rabbits and the results of the t-test demonstrated insignificant variation in pharmacokinetic parameters among the two formulations, confirming that the prepared tablet showed sustained-release profile. CONCLUSION: The results indicated that karaya and locust bean gum can be effectively used to formulate sustained-release tablets.

Engineering of Nanospheres Dispersed Microneedle System for Antihypertensive Action.

BACKGROUND: A combinational therapy is mostly preferred in hypertension treatment because of low-dose and less side effects like pretibial edema, and gastrointestinal bleeding. OBJECTIVE: So the objective of the present work was to formulate an advanced drug delivery system in the form of bio-responsive microneedles by incorporating nifedipine, a cardiodepressant and diltiazem, a vasodilator for effective synergism in the treatment of hypertension. METHODS: The pH-responsive PLGA nanospheres of diltiazem were formulated using Water-in-Oil-in- Water (W/O/W) double emulsion and solvent-diffusion-evaporation technique. These nanospheres were added to nifedipine-PVP mixture and then incorporated into mold to develop microneedles. RESULTS: The microneedles showed the release of nifedipine almost 96.93± 2.31% for 24 h due to high PVP solubilization. The nanospheres of diltiazem on contact with acidic pH of skin managed to form of CO2 bubbles and increase the internal pressure to burst PLGA shell due to pore formation. The mean blood pressure observed for the normal group was 89.58 ± 3.603 mmHg, whereas the treatment with the new formulation significantly reduced the mean blood pressure up to 84.11 ± 2.98 mmHg in comparison to the disease control group (109.9 ± 1.825 mm Hg). CONCLUSION: This system co-delivers the drugs nifedipine and diltiazem in hypertension and shows an advance alternative approach over conventional drug delivery system.

Predicting Clinical Effects of CYP3A4 Modulators on Abemaciclib and Active Metabolites Exposure Using Physiologically Based Pharmacokinetic Modeling.

Abemaciclib, a selective inhibitor of cyclin-dependent kinases 4 and 6, is metabolized mainly by cytochrome P450 (CYP)3A4. Clinical studies were performed to assess the impact of strong inhibitor (clarithromycin) and inducer (rifampin) on the exposure of abemaciclib and active metabolites. A physiologically based pharmacokinetic (PBPK) model incorporating the metabolites was developed to predict the effect of other strong and moderate CYP3A4 inhibitors and inducers. Clarithromycin increased the area under the plasma concentration-time curve (AUC) of abemaciclib and potency-adjusted unbound active species 3.4-fold and 2.5-fold, respectively. Rifampin decreased corresponding exposures 95% and 77%, respectively. These changes influenced the fraction metabolized via CYP3A4 in the model. An absolute bioavailability study informed the hepatic and gastric availability. In vitro data and a human radiolabel study determined the fraction and rate of formation of the active metabolites as well as absorption-related parameters. The predicted AUC ratios of potency-adjusted unbound active species with rifampin and clarithromycin were within 0.7- and 1.25-fold of those observed. The PBPK model predicted 3.78- and 7.15-fold increases in the AUC of the potency-adjusted unbound active species with strong CYP3A4 inhibitors itraconazole and ketoconazole, respectively; and 1.62- and 2.37-fold increases with the concomitant use of moderate CYP3A4 inhibitors verapamil and diltiazem, respectively. The model predicted modafinil, bosentan, and efavirenz would decrease the AUC of the potency-adjusted unbound active species by 29%, 42%, and 52%, respectively. The current PBPK model, which considers changes in unbound potency-adjusted active species, can be used to inform dosing recommendations when abemaciclib is coadministered with CYP3A4 perpetrators.

Food-Drug Interaction between the Adlay Bran Oil and Drugs in Rats.

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) contains various phytonutrients for treating many diseases in Asia. To investigate whether orally administered adlay bran oil (ABO) can cause drug interactions, the effects of ABO on the pharmacokinetics of five cytochrome P450 (CYP) probe drugs were evaluated. Rats were given a single oral dose (2.5 mL/kg BW) of ABO 1 h before administration of a drug cocktail either orally or intravenously, and blood was collected at various time points. A single oral dose of ABO administration did not affect the pharmacokinetics of five probe drugs when given as a drug cocktail intravenously. However, ABO increased plasma theophylline (+28.4%), dextromethorphan (+48.7%), and diltiazem (+46.7%) when co-administered an oral drug cocktail. After 7 days of feeding with an ABO-containing diet, plasma concentrations of theophylline (+45.4%) and chlorzoxazone (+53.6%) were increased after the oral administration of the drug cocktail. The major CYP enzyme activities in the liver and intestinal tract were not affected by ABO treatment. Results from this study indicate that a single oral dose or short-term administration of ABO may increase plasma drug concentrations when ABO is given concomitantly with drugs. ABO is likely to enhance intestinal drug absorption. Therefore, caution is needed to avoid food-drug interactions between ABO and co-administered drugs.

Effect of CYP3A Inhibition and Induction on the Pharmacokinetics of Suvorexant: Two Phase I, Open-Label, Fixed-Sequence Trials in Healthy Subjects.

BACKGROUND AND OBJECTIVES: Suvorexant is an orexin receptor antagonist indicated for the treatment of insomnia, characterized by difficulties with sleep onset and/or sleep maintenance. As suvorexant is metabolized primarily by Cytochrome P450 3A (CYP3A), and its pharmacokinetics may be affected by CYP3A modulators, the effects of CYP3A inhibitors (ketoconazole or diltiazem) or an inducer (rifampin [rifampicin]) on the pharmacokinetics, safety, and tolerability of suvorexant were investigated. METHODS: In two Phase I, open-label, fixed-sequence trials (Studies P008 and P038), healthy subjects received a single oral dose of suvorexant followed by co-administration with multiple once-daily doses of strong/moderate CYP3A inhibitors (ketoconazole/diltiazem) or a strong CYP3A inducer (rifampin). Treatments were administered in the morning: suvorexant 4 mg with ketoconazole 400 mg (Study P008; N = 10), suvorexant 20 mg with diltiazem 240 mg (Study P038; N = 20), and suvorexant 40 mg with rifampin 600 mg (Study P038; N = 10). Area under the plasma concentration-time curve from time zero to infinity (AUC0-∞), maximum plasma concentration (Cmax), half-life (t½), and time to Cmax (tmax) were derived from plasma concentrations of suvorexant collected at prespecified time points up to 10 days following CYP3A inhibitor/inducer co-administration. Adverse events (AEs) were recorded. RESULTS: Co-administration with ketoconazole resulted in increased exposure to suvorexant [AUC0-∞: geometric mean ratio (GMR); 90% confidence interval (CI) 2.79 (2.35, 3.31)] while co-administration with diltiazem resulted in a lesser effect [GMR (90% CI): 2.05 (1.82, 2.30)]. Co-administration with rifampin led to a marked decrease (88%) in suvorexant exposure. Consistent with morning administration and known suvorexant pharmacology, somnolence was the most frequently reported AE. CONCLUSIONS: These results are consistent with expectations that strong CYP3A inhibitors and inducers exert marked effects on suvorexant pharmacokinetics. In the context of a limited sample size, single suvorexant doses were generally well tolerated in healthy subjects when co-administered with/without a CYP3A inhibitor/inducer.

The Influence of Microneedles on the Percutaneous Penetration of Selected Antihypertensive Agents: Diltiazem Hydrochloride and Perindopril Erbumine.

BACKGROUND: It is well documented in the scientific literature that high blood pressure can lead to cardiovascular disease. Untreated hypertension has clinical consequences such as coronary artery disease, stroke or kidney failure. Diltiazem hydrochloride (DH), a calcium-channel blocker, and perindopril erbumine (PE), an inhibitor of the angiotensin converting enzyme are used for the management of hypertension. OBJECTIVE: This project will examine the effect of microneedle rollers on the transport of DH and PE across pig ear skin. The use of the transcutaneous route of administration reduces and in sometimes eliminates the trauma and pain associated with injections. Furthermore, there is increased patient compliance. The purpose of this project was to study the effect of stainless steel microneedles on the transdermal delivery of DH and PE. METHOD: We utilized vertical Franz diffusion cells to study in vitro transport of DH and PE across microneedle- treated pig ear skin. Confocal laser scanning microscopy (CLSM) was used to characterize microchannel depth. Transdermal flux values were determined from the slope of the linear portion of the cumulative amount versus time curve. RESULTS: There was a 113.59-fold increase in the transdermal permeation of DH following the application of microneedle roller compared to passive diffusion. CONCLUSION: In the case of PE, there was an 11.99-fold increase in the drug transport across pig skin following the application of microneedle rollers in comparison with passive diffusion. Student's t-test and Mann-Whitney's rank sum test were used to determine statistically significant differences between experimental and control groups.

Multi-purposable filaments of HPMC for 3D printing of medications with tailored drug release and timed-absorption.

Three-dimensional printing (3DP), though developed for nonmedical applications and once regarded as futuristic only, has recently been deployed for the fabrication of pharmaceutical products. However, the existing feeding materials (inks and filaments) that are used for printing drug products have various shortcomings, including the lack of biocompatibility, inadequate extrudability and printability, poor drug loading, and instability. Here, we have sought to develop a filament using a single pharmaceutical polymer, with no additives, which can be multi-purposed and manipulated by computational design for the preparation of tablets with desired release and absorption patterns. As such, we have used hydroxypropyl-methylcellulose (HPMC) and diltiazem, a model drug, to prepare both drug-free and drug-impregnated filaments, and investigated their thermal and crystalline properties, studied the cytotoxicity of the filaments, designed and printed tablets with various infill densities and patterns. By alternating the drug-free and drug-impregnated filaments, we fabricated various types of tablets, studied the drug release profiles, and assessed oral absorption in rats. Both diltiazem and HPMC were stable at extrusion and printing temperatures, and the drug loading was 10% (w/w). The infill density, as well as infill patterns, influenced the drug release profile, and thus, when the infill density was increased to 100%, the percentage of drug released dramatically declined. Tablets with alternating drug-free and drug-loaded layers showed delayed and intermittent drug release, depending on when the drug-loaded layers encountered the dissolution media. Importantly, the oral absorption patterns accurately reproduced the drug release profiles and showed immediate, extended, delayed and episodic absorption of the drug from the rat gastrointestinal tract (GIT). Overall, we have demonstrated here that filaments for 3D printers can be prepared from a pharmaceutical polymer with no additives, and the novel computational design allows for fabricating tablets with the capability of producing distinct absorption patterns after oral administration.

Population Pharmacokinetic Modeling of Diltiazem in Chinese Renal Transplant Recipients.

BACKGROUND AND OBJECTIVES: Diltiazem is a benzothiazepine calcium blocker and widely used in renal transplant patients since it improves the level of tacrolimus or cyclosporine A concentration. Several population pharmacokinetic (PopPK) models had been established for cyclosporine A and tacrolimus but no specific PopPK model was established for diltiazem. The aim of the study is to develop a PopPK model for diltiazem in renal transplant recipients and provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study. METHODS: Patients received tacrolimus as primary immunosuppressant agent after renal transplant and started administration of diltiazem 90 mg twice daily on 5th day. The concentration of diltiazem at 0, 0.5, 1, 2, 8, and 12 h was measured by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Genotyping for CYP3A4*1G, CYP3A5*3, and MDR1 3435 was conducted by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). 25 covariates were considered in the stepwise covariate model (SCM) building procedure. RESULTS: One-compartment structural pharmacokinetic model with first-order absorption and elimination was used to describe the pharmacokinetic characteristics of diltiazem. Total bilirubin (TBIL) influenced apparent volume of distribution (V/F) of diltiazem in the forward selection. The absorption rate constant (K a), V/F, and apparent oral clearance (CL/F) of the final population pharmacokinetic (PopPK) model of diltiazem were 1.96/h, 3550 L, and 92.4 L/h, respectively. CONCLUSION: A PopPK model of diltiazem is established in Chinese renal transplant recipients and it will provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study.

Enhanced Oral Bioavailability of Diltiazem by the Influence of Gallic Acid and Ellagic Acid in Male Wistar Rats: Involvement of CYP3A and P-gp Inhibition.

The oral bioavailability of diltiazem is very low due to rapid first pass metabolism in liver and intestine. The purpose of the study was to investigate the effect of gallic acid and ellagic acid on intestinal transport and oral bioavailability of diltiazem in rats. The intestinal transport and permeability of diltiazem was evaluated by in vitro non-everted sac method and in situ single pass intestinal perfusion study. The oral pharmacokinetics was evaluated by conducting oral bioavailability study. The intestinal transport and apparent permeability of diltiazem were significantly enhanced in duodenum, jejunum, and ileum of gallic and ellagic acid-treated groups. The effective permeability of diltiazem was significantly enhanced in ileum part of gallic and ellagic acid-treated groups. When compared with control group, the presence of these two phytochemicals significantly enhanced the area under plasma concentration-time curve and the peak plasma concentration of diltiazem (Cmax ). Gallic acid and ellagic acid significantly increased the bioavailability of diltiazem due to the inhibition of both CYP3A-mediated metabolism and P-glycoprotein-mediated efflux in the intestine and/or liver. Based on these results, the clinical experiments are warranted for the confirmation to reduce the dose of diltiazem when concomitantly administered with these phytochemicals. Copyright © 2017 John Wiley & Sons, Ltd.

Ionic liquids as potential enhancers for transdermal drug delivery.

The aim of this study was to verify the effect of several cyclic onium based ionic liquids (ILs), including mono- and dicationic derivatives of 1,4-diazabicyclo[2.2.2]octane (DABCO), a dialkyl morpholinium salt and a Brønsted acidic IL, as enhancers of the in vitro transdermal permeation and skin retention of diltiazem through and into hairless rat skin. The drug was used as both the hydrochloride salt (DZHCl) and the free base (DZB) to highlight the relationship between the enhancement effect and the physico-chemical characteristics of the active agent. Permeation tests were carried out using Gummer-type diffusion cells and excised rat skin with a 0.005M aqueous solution of diltiazem hydrochloride or diltiazem free base with and without the addition of 1% w/w ionic liquids. At the end of the permeation experiments with diltiazem hydrochloride, a suitable extraction procedure allowed for the determination of the drug content retained in the skin. Depending on the ionic liquid structure, a significant enhancement in diltiazem hydrochloride levels in the receiving phase was observed, and the transdermal permeation of the diltiazem free base was markedly increased by treatment with all of the ionic liquids. N-dodecyldabco bromide was the best enhancer for both salified and free base drug forms, even though it showed a certain toxicity. On the other hand, N-methyl-N-decylmorpholinium bromide showed a good balance between enhancer activity and cytotoxicity.

Risk-based approach for systematic development of gastroretentive drug delivery system.

The research envisioned was the development of diltiazem hydrochloride effervescent floating matrix tablet using a risk-based approach. Preliminarily, the in vitro drug release profile was derived which theoretically simulated the in vivo condition after oral administration. Considering this as a rationale, the formulation development was initiated with defining the quality target product profile (QTPP) and critical quality attributes (CQAs). The preliminary studies were conducted to screen material attributes and process parameters followed by their risk assessment studies to select the plausible factors affecting the drug product CQAs, i.e., floating lag time and drug release profile. A 3(2) full factorial design was used to estimate the effect of the amount of swelling polymer (X 1) and gas-generating agent (X 2) on percent drug release (Q t1h and Q t8h) and floating lag time. Response and interaction plots were generated to examine the variables. Selection of an optimized formulation was done using desirability function and further validated. The model diagnostic plots represent the absence of outliers. The optimized formula obtained by the software was further validated, and the result of drug release and floating lag time was close to the predicted values. In a clear and concise way, the current investigations report the successful development of an effervescent floating matrix tablet for twice daily administration of diltiazem hydrochloride.

Significant impacts of CYP3A4*1G and CYP3A5*3 genetic polymorphisms on the pharmacokinetics of diltiazem and its main metabolites in Chinese adult kidney transplant patients.

WHAT IS KNOWN AND OBJECTIVE: The calcium channel blocker diltiazem has been used widely as a cyclosporine (CsA)/tacrolimus-sparing agent. However, considerable interpatient variability in diltiazem's CsA/tacrolimus-sparing effect has been observed in many clinical studies. This study was carried out to investigate the impacts of the CYP3A4*1G and CYP3A5*3 genetic polymorphisms on the trough concentration/dose ratios and pharmacokinetics of diltiazem and its main metabolites in Chinese adult renal transplant patients. METHODS: Two hundred and twenty-five Chinese renal transplant patients were genotyped for CYP3A4*1G and CYP3A5*3. The predose and post-dose plasma concentrations of diltiazem and its main metabolisms were determined by HPLC. The relationships between the genotypes and pharmacokinetics were investigated. RESULTS AND DISCUSSION: The dose-adjusted concentrations and pharmacokinetics of diltiazem and its main metabolites were significantly affected by CYP3A4 *1G and CYP3A5*3 alleles. Patients with a CYP3A4*1/*1 genotype were found to have a higher dose-adjusted trough concentration and AUC of diltiazem and its main metabolites compared with those with CYP3A4*1G*1G(P<0·05). The dose-adjusted trough levels and AUC of diltiazem and its main metabolites were significantly lower in CYP3A5*1*1 carriers than in CYP3A5*3 carriers (P < 0·05). WHAT IS NEW AND CONCLUSION: The CYP3A4*1G and CYP3A5*3 genetic polymorphisms are closely related to the trough concentration/dose ratios and pharmacokinetics of diltiazem and its main metabolites in Chinese adult renal transplant patients.

Pluronic lecithin organogel (PLO) of diltiazem hydrochloride: effect of solvents/penetration enhancers on ex vivo permeation.

In the present study, pluronic lecithin organogel (PLO) of diltiazem hydrochloride (DZH) was developed by taking different ratios of organic phase to aqueous phase (1:3, 1:4, and 1:5) with varying concentration of soya lecithin (20, 30, and 40 % w/w) in organic phase (isopropyl myristate, IPM) and pluronic (20, 25, and 30 % w/w) in aqueous phase, respectively, and characterized for in vitro parameters and ex vivo permeation study. The results of in vitro parameters were found to be within permissible limit and all the PLOs were physically stable at refrigeration and ambient temperature. The influence of phase ratio and different concentrations of soya lecithin on DZH release from the PLOs was found to be significant (p < 0.05), whereas the influences of different concentrations of pluronic were insignificant. The effect of different solvents/penetration enhancers viz. IPM, propylene glycol (PG), dimethyl sulphoxide (DMSO), and D-limonene, in combination and alone, on the permeation of DZH across the dorsal skin of rat was studied. Among all, formulation containing IPM (PLO6) exhibited highest flux of 147.317 µg/cm(2)/h. Furthermore, histopathology section of treated skin sample illustrated that lipid bilayer disruption was the mechanism for the DZH permeation. The above results indicated that PLO6 may serve as a promising alternative delivery system for DZH in the effective treatment of hypertension.

Bioconcentration, metabolism and half-life time of the human therapeutic drug diltiazem in rainbow trout Oncorhynchus mykiss.

Diltiazem is a human therapeutic drug and a member of the group of calcium channel blockers having widespread use in the treatment of angina pectoris and hypertension. The objective of the present study was to assess the bioconcentration, metabolism, and half-life time of diltiazem in rainbow trout Oncorhynchus mykiss. Juvenile trout were exposed for 21 and 42 days to three nominal concentrations of diltiazem: 0.03 µg L(-1) (environmentally relevant concentration), 3 µg L(-1), and 30 µg L(-1) (sub-lethal concentrations). The bioconcentration factor (BCF) of diltiazem was relatively low (0.5-194) in analysed tissues, following the order kidney > liver > muscle > blood plasma. The half-life of diltiazem in liver, kidney, and muscle was 1.5 h, 6.2 h, and 49 h, respectively. The rate of metabolism for diltiazem in liver, kidney, muscle, and blood plasma was estimated to be 85 ± 9%, 64 ± 14%, 46 ± 6%, and 41 ± 8%, respectively. Eight diltiazem metabolites were detected. The presence of desmethyl diltiazem (M1), desacetyl diltiazem (M2), and desacetyl desmethyl diltiazem (M3) suggests that rainbow trout metabolize diltiazem mainly via desmethylation and desacetylation, similar to mammals. In addition, diltiazem undergoes hydroxylation in fish. At environmentally relevant concentrations, diltiazem and its metabolites were identified in liver and kidney, indicating the potential for uptake and metabolism in non-target organisms in the aquatic environment.

Late sodium current block for drug-induced long QT syndrome: Results from a prospective clinical trial.

Drug-induced long QT syndrome has resulted in many drugs being withdrawn from the market. At the same time, the current regulatory paradigm for screening new drugs causing long QT syndrome is preventing drugs from reaching the market, sometimes inappropriately. In this study, we report the results of a first-of-a-kind clinical trial studying late sodium (mexiletine and lidocaine) and calcium (diltiazem) current blocking drugs to counteract the effects of hERG potassium channel blocking drugs (dofetilide and moxifloxacin). We demonstrate that both mexiletine and lidocaine substantially reduce heart-rate corrected QT (QTc) prolongation from dofetilide by 20 ms. Furthermore, all QTc shortening occurs in the heart-rate corrected J-Tpeak (J-Tpeak c) interval, the biomarker we identified as a sign of late sodium current block. This clinical trial demonstrates that late sodium blocking drugs can substantially reduce QTc prolongation from hERG potassium channel block and assessment of J-Tpeak c may add value beyond only assessing QTc.

An Assessment of the Oral Bioavailability of Three Ca-Channel Blockers Using a Cassette-Microdose Study: A New Strategy for Streamlining Oral Drug Development.

A cassette-microdose (MD) clinical study was performed to demonstrate its usefulness for identifying the most promising compound for oral use. Three Ca-channel blockers (nifedipine, nicardipine, and diltiazem) were chosen as model drugs. In the MD clinical study, a cassette-dose method was employed in which three model drugs were administered simultaneously. Both intravenous (i.v.) and oral (p.o.) administration studies were conducted to calculate the oral bioavailability (BA). For comparison, p.o. studies with therapeutic dose (ThD) levels were also performed. In all studies, blood concentrations of each drug were successfully determined using liquid chromatography-mass spectrometry with the lower limit of quantification of 0.2-2.0 pg/mL. Oral BA of nifedipine in the MD study was approximately 50% and in the same range with that obtained in the ThD study, whereas other two drugs showed significantly lower BA in the MD study, indicating a dose-dependent absorption. In addition, compared with the ThD study, absorption of nicardipine was delayed in the MD study. As a result, nifedipine was considered to be most promising for oral use. In conclusion, a cassette-MD clinical study is of advantage for oral drug development that enables to identify the candidate having desired properties for oral use.

Characterization of Species Differences in Tissue Diltiazem Deacetylation Identifies Ces2a as a Rat-Specific Diltiazem Deacetylase.

Diltiazem, a calcium channel blocker, is mainly metabolized via demethylation or deacetylation in humans. Diltiazem demethylation is catalyzed by cytochrome P450 2D6 and 3A4. Although it was previously reported that the area under the curve ratio of deacetyldiltiazem to diltiazem after oral dosing with diltiazem in rats was sevenfold higher than in humans, the molecular mechanisms underlying this species difference remain to be clarified. In the present study, we compared the diltiazem deacetylase activity in liver, intestinal, renal, and pulmonary microsome preparations of human and experimental animal tissues to identify the specific deacetylase enzyme(s) involved in deacetylation. Diltiazem deacetylase activity was detected in rat liver and small intestine microsome preparations, but not in those from human, monkey, dog, and mouse tissues. Further purification of rat liver microsome (RLM) proteins identified four carboxylesterase (Ces) enzymes (Ces1d, Ces1e, Ces1f, and Ces2a) as potential candidate deacetylases. On the basis of their tissue distribution, the Ces2a enzyme was considered to be the enzyme that was responsible for diltiazem deacetylation. Furthermore, recombinant rat Ces2a expressed in Sf21 cells displayed efficient diltiazem deacetylase activity with similar Km values as RLM. In addition, the inhibitory characteristics of various chemical inhibitors were similar between recombinant rat Ces2a and RLM. In conclusion, we determined that only rat tissues were able to catalyze diltiazem deacetylation. The characterization of Ces enzymes in animal species, as undertaken in this study, will prove useful to predict the species-specific pharmacokinetics differences between the in vivo models used for drug development.

Novel orally swallowable IntelliCap(®) device to quantify regional drug absorption in human GI tract using diltiazem as model drug.

Typically, colonic absorption of a drug is mandatory for a sustained release formulation to hold the drug's plasma level for more than 12 or 24 h above the minimum therapeutic plasma concentration (efficacy). According to Drugs@FDA, only 7.4% of the oral drugs are extended release forms probably showing colonic absorption. Therefore an early determination of a drug's colonic absorption using the IntelliCap® in animals or humans will provide the mandatory information to initiate or stop a SR form development. Diltiazem (60 mg) is used in the oral swallowable IntelliCap® and the marketed SR form from Mylan (coated beads). A human study with 14 healthy volunteers compared the Mylan formulation with the IntelliCap® device that releases the drug identical to the in-vitro dissolution of the Mylan product. The plasma profiles of IntelliCap® and Mylan formulation are highly similar. The mean AUC (bioequivalence fulfilled) and mean Cmax of IntelliCap® shows only a difference of +15% and -12%, respectively. But the PK profile of the Mylan formulation shows a broader peak around Cmax. About 81.8% diltiazem was absorbed in the colon (IntelliCap®) comparable to former publications. The Mylan is a SR diffusion coated beads form whereas the IntelliCap® is a monolithic capsule. The beads are transported in the gut and spread which results in a longer Tmax and a broader Cmax peak. The IntelliCap® device can quantitatively measure the colonic absorption of a drug in excellent accordance to a standard oral SR dosage form.