The influence of pretreatment periods with diltiazem on nifedipine kinetics

Virtual Clinical Trials Guided Design of an Age-Appropriate Formulation and Dosing Strategy of Nifedipine for Paediatric Use

The rapid onset of action of nifedipine causes a precipitous reduction in blood pressure leading to adverse effects associated with reflex sympathetic nervous system (SNS) activation, including tachycardia and worsening myocardial and cerebrovascular ischemia. As a result, short acting nifedipine preparations are not recommended. However, importantly, there are no modified release preparations of nifedipine authorised for paediatric use, and hence a paucity of clinical studies reporting pharmacokinetics data in paediatrics. Pharmacokinetic parameters may differ significantly between children and adults due to anatomical and physiological differences, often resulting in sub therapeutic and/or toxic plasma concentrations of medication. However, in the field of paediatric pharmacokinetics, the use of pharmacokinetic modelling, particularly physiological-based pharmacokinetics (PBPK), has revolutionised the ability to extrapolate drug pharmacokinetics across age groups, allowing for pragmatic determination of paediatric plasma concentrations to support drug licensing and clinical dosing. In order to pragmatically assess the translation of resultant dissolution profiles to the paediatric populations, virtual clinical trials simulations were conducted. In the context of formulation development, the use of PBPK modelling allowed the determination of optimised formulations that achieved plasma concentrations within the target therapeutic window throughout the dosing strategy. A 5 mg sustained release mini-tablet was successfully developed with the duration of release extending over 24 h and an informed optimised dosing strategy of 450 µg/kg twice daily. The resulting formulation provides flexible dosing opportunities, improves patient adherence by reducing frequent administration burden and enhances patient safety profiles by maintaining efficacious levels of consistent drug plasma levels over a sustained period of time.

Investigating the interaction between nifedipine- and ritonavir-containing antiviral regimens: A physiologically based pharmacokinetic/pharmacodynamic analysis

AIMS

Hypertension is a common comorbidity of patients with COVID-19, SARS or HIV infection. Such patients are often concomitantly treated with antiviral and antihypertensive agents, including ritonavir and nifedipine. Since ritonavir is a strong inhibitor of CYP3A and nifedipine is mainly metabolized via CYP3A, the combination of ritonavir and nifedipine can potentially cause drug-drug interactions. This study provides guidance on nifedipine treatment during and after coadministration with ritonavir-containing regimens, using a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) analysis.

METHODS

The PBPK/PD models for 3 formations of nifedipine were developed based on the Simcyp nifedipine model and the models were verified using published data. The effects of ritonavir on nifedipine exposure and systolic blood pressure (SBP) were assessed for instant-release, sustained-release and controlled-release formulations in patients. Various nifedipine regimens were investigated when coadministered with or without ritonavir.

RESULTS

PBPK/PD models for 3 formulations of nifedipine were successfully established. The predicted maximum concentration (C_max ), area under plasma concentration-time curve (AUC), maximum reduction in SBP and area under effect-time curve were all within 0.5-2.0-fold of the observed data. Model simulations showed that the inhibitory effect of ritonavir on CYP3A4 increased the C_max of nifedipine 17.92-48.85-fold and the AUC 63.30-84.01-fold at steady state and decreased the SBP by >40 mmHg. Thus, the combination of nifedipine and ritonavir could lead to severe hypotension.

CONCLUSION

Ritonavir significantly affects the pharmacokinetics and antihypertensive effect of nifedipine. It is not recommended for patients to take nifedipine- and ritonavir-containing regimens simultaneously.

Effect of the Treatment Period With Erythromycin on Cytochrome P450 3A Activity in Humans

The aim of the present study was to estimate the time course change in cytochrome P450 3A (CYP3A) activity during repeated doses of erythromycin. Twelve healthy male volunteers participated in this randomized, 4 x 4 Latin square design study. The pharmacokinetics of a single oral dose of midazolam, a probe for CYP3A activity, were assessed in 4 conditions: (1) midazolam (5 mg) without erythromycin (EM0), (2) erythromycin 2 days + midazolam (2.5 mg) (EM2), (3) erythromycin 4 days + midazolam (2.5 mg) (EM4), and (4) erythromycin 7 days + midazolam (2.5 mg) (EM7). The dose of erythromycin was 800 mg/d. Erythromycin produced a 2.3-, 3.4-, and 3.4-fold increase in dose-corrected area under the curve of midazolam for EM2, EM4, and EM7, respectively, as compared with EM0 (P <.05/6). A significant prolongation of terminal half-life was observed in EM4 and EM7. The relationship between the duration of erythromycin treatment and total clearance of midazolam indicated that a plateau level of CYP3A inhibition can be achieved by 4 days or more of erythromycin treatment. The repeated treatment with erythromycin yields CYP3A inhibition in a duration-dependent manner. A 4-day course of erythromycin treatment produces 90% or more of the maximal inhibition of CYP3A in humans.

Current concepts of pharmacotherapy in hypertension: combination calcium channel blocker therapy in the treatment of hypertension

Effective control of blood pressure is usually achieved only with the use of two or more antihypertensive medications. The treatment options for hypertension are numerous, and the number of possible combinations large. The selection of a specific combination drug regimen has often been linked to the perceived need for diuretic therapy as first- or second-step therapy; thus, the popularity of such drug combinations as an angiotensin-converting enzyme (ACE) inhibitor/diuretic, an angiotensin-receptor blocker/diuretic, or a beta blocker/diuretic. Rational alternatives exist, including an ACE inhibitor/calcium channel blocker (CCB) or a dihydropyridine CCB/b blocker combination. Traditionally, recommendations have advised against the use of combination therapy with two drugs from the same therapeutic class. However, because of the different binding and pharmacologic characteristics of CCBs, a rationale exists for combining different agents in this class in the management of hypertension and/or symptomatic coronary artery disease. In the treatment of either hypertension or angina, combination CCB therapy can prove uniquely successful.

Enhanced cholesterol reduction by simvastatin in diltiazem-treated patients

AIMS

To investigate whether an interaction between diltiazem and the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin may enhance the cholesterol-lowering response to simvastatin in diltiazem-treated patients.

METHODS

One hundred and thirty-five patients attending the Sheffield hypertension clinic who started consecutively on simvastatin for primary or secondary prevention of coronary heart disease (CHD) during the 2 years June, 1996-May 1998 were surveyed. From the clinic records we extracted and recorded absolute and percentage cholesterol responses to the starting dose of simvastatin and coprescription of diltiazem.

RESULTS

The cholesterol reduction for the 19 patients on diltiazem was 33.3% compared with 24.7% in the remaining 116 patients (median difference 8.6%, 95% CI 1.1-12.2%, P<0.02). The interindividual variability of cholesterol response to simvastatin was greater for patients not taking diltiazem than for those patients taking diltiazem. The ratio of the variances in response for the nondiltiazem group relative to the diltiazem group was 1.34 at 10 mg simvastatin daily (not significant, 95% CI 0.16-4.11), and 3.42 at 20 mg daily (P<0.01, 95% CI 1.26-7.18). Concurrent diltiazem therapy (P<0.04), age (P=0.001) and starting dose of simvastatin (P=0.002) were found to be significant independent predictors of percentage cholesterol response.

CONCLUSIONS

Patients who take both simvastatin and diltiazem may need lower doses of simvastatin to achieve the recommended reduction in cholesterol. The pharmacokinetic and pharmacodynamic aspects of this interaction need further study to confirm an enhanced effect on cholesterol reduction, and exclude an increased risk of adverse events.

Comparison of nifedipine alone and with diltiazem or verapamil in hypertension

Receptor binding studies suggest that combinations of calcium channel blockers may result in either enhanced or diminished pharmacological effects, but clinical data in hypertension are incomplete. In this study, we compared blood pressure reductions using nifedipine alone, nifedipine plus diltiazem, and nifedipine plus verapamil and determined whether combinations alter nifedipine pharmacokinetics. After determination of baseline blood pressures. 16 subjects with essential hypertension (12 men, 4 women; mean age, 48 years) received 30 mg/d open-label, sustained release nifedipine for 2 weeks. If still hypertensive (n = 16), they were randomized (double-blind) to receive either additional sustained release diltiazem or sustained release verapamil, both 180 mg/d, for 2 weeks and were then crossed-over for the final 2 weeks of the study. All medications were once-daily, extended-release formulations. Blood pressures and nifedipine plasma concentrations were measured during the final day of each treatment. Overall, each combination lowered mean systolic and diastolic pressures more than nifedipine alone. Mean supine diastolic pressures were significantly lower at 8 hours (77.6 versus 84.6 mm Hg, P = .001) and 12 hours (81.5 versus 87.1 mm Hg, P = .04) with nifedipine plus diltiazem than nifedipine plus verapamil. Mean nifedipine concentrations were inversely correlated with mean blood pressures. Mean nifedipine area under the curve values were greater with diltiazem than verapamil (1430 versus 1134 ng.h/mL, P = .026), with each greater than nifedipine alone (957 ng.h/mL). Nifedipine plus diltiazem had a greater antihypertensive effect than nifedipine plus verapamil. Diltiazem caused greater increases in nifedipine plasma concentrations than did verapamil. These data suggest that combined calcium channel blockers result in additive antihypertensive effects, perhaps because of a pharmacokinetic interaction.