Pharmacokinetic analysis of two new sustained-release products of diltiazem designed for twice- and once-daily treatment

The pharmacokinetics of extended-release formulations of calcium antagonists and of amlodipine in subjects with different gastrointestinal transit times

The influence of gastrointestinal (GI) transit times on the pharmacokinetics (PK) of three calcium channel blockers (CCBs), recommended for once-daily dosing, was investigated. In a three-way crossover design, the single-dose PK of a controlled-delivery formulation of 240 mg diltiazem (DIL), an extended-release formulation of 10 mg felodipine (FEL), and 5 mg amlodipine (AML) were compared in two groups of healthy subjects, with either slow (> 35 h) or rapid (< 15 h) GI transit, as assessed by the metal detector method (EAS II). GI transit significantly affected the PK of DIL. Mean PK parameters in the rapid versus slow transit group were the following: trough levels (C24 h): 22.8 +/- 8.3 versus 49.5 +/- 35.7 ng/ml, p < 0.05; AUC 1134.4 +/- 512.7 versus 1704.7 +/- 1185.6 hng/ml, p < 0.05 (one-sided). Neither AUC nor trough levels of FEL and AML were significantly influenced by transit times, nor was Cmax after any of the three treatments. Variations in PK parameters, as indicated by coefficients of variation, were about twofold higher for both DIL and FEL, compared to AML. Variations in mean residence times were significantly lower for AML compared to DIL and FEL (7% vs. 30% and 17%, p < 0.001 and p < 0.002, respectively). Peak-to-trough ratios (Cmax/C24 h mean) were 1.8 +/- 0.9 for DIL, 7.6 +/- 3.5 for FEL, and 1.7 +/- 0.2 for AML. In conclusion, the predictability of pharmacokinetic behavior both in conditions of rapid or slow GI transit is optimized in drugs with intrinsically slow elimination such as amlodipine. The pharmacokinetics of the CCBs with formulation-based once-a-day characteristics are sensitive to GI transit if these processes are rapid enough to interfere with the formulation-specific release profile.

Trough-to-peak ratio and circadian blood pressure profile after treatment with once-daily extended-release diltiazem, 240 mg, in patients with mild-to-moderate essential hypertension

Once-daily diltiazem extended-release 240 mg (Lacerol-HTA Retard) was evaluated for safety, efficacy, and trough-to-peak ratio in a multicenter open study by using 24-h blood pressure (BP) monitoring in mild-to-moderate essential hypertension. After a 4-week washout period, 30 patients (17 men, 13 women) aged 25-76 years, showing a mean daytime diastolic BP (DBP) >90 mm Hg, were treated with diltiazem-ER, 240 mg, given once daily for 8 weeks. Ambulatory BP monitoring was obtained at the end of a 4-week placebo run-in period and during the last week of treatment. A significant reduction of the mean values of clinical BP [161.6 +/- 16.2 to 151.2 +/- 15.6 mm Hg; p < 0.01 for systolic BP (SBP); and 101.1 +/- 4.8 to 93.3 +/- 9.2 mm Hg; p < 0.001 for DBP] was observed at the end of treatment in the group of 30 patients, with no significant changes in heart rate (77.1 +/- 9.9 to 73.1 +/- 11.1 beats/min; p = NS). Likewise, mean values of 24-h SBP, DBP, SBP-load, and DBP-load were significantly reduced. In the group of 21 responders, the average reduction at peak was -18.6 +/- 12.9 mm Hg for SBP and -14.7 +/- 9.5 mm Hg for DBP. The residual effect at trough was -12.2 +/- 14.7 and -8.1 +/- 10 mm Hg, respectively. The trough-to-peak ratio was estimated as 0.66 for SBP and 0.55 for DBP. Long-term variability expressed as the mean standard deviation of BP for the 24-h period was reduced in responders (16.2 +/- 4.3 to 14.6 +/- 2.7 mm Hg for SBP; p = 0.0395; and 12.1 +/- 2.7 to 10.7 +/- 2.5 mm Hg for DBP; p = 0.0019), although no changes were observed in the variation coefficient (10.58-10.57% for SBP and 12.88-12.87% for DBP). We conclude that once-daily diltiazem-ER, 240 mg, was effective and well tolerated. Blood pressure was controlled over the entire period of 24 h, preserving the circadian profile and reducing long-term variability in responders. The significant reduction of both BP values and long-term variability may have implications involving protection from end-organ damage in essential hypertension.

Advanced and controlled drug delivery systems in clinical disease management

Advanced and controlled drug delivery systems are important for clinical disease management. In this review the most important new systems which have reached clinical application are highlighted. Microbiologically controlled drug delivery is important for gastrointestinal diseases like ulcerative colitis and distally localized Crohn's disease. In cardiology the more classic controlled release systems have improved patient compliance and decreased side effects. In the treatment of intractable pain the spinal and transdermal route is well documented. In neurology the flattened peak-through levels of antiepileptic drugs and anti Parkinson's drugs represents a more predictable kinetic profile. Tracheal delivery of corticosteroids and sympaticomimetics in asthma and Chronic Obstructive Pulmonary Disease is fully accepted in clinical practice: delivery by this route results in better efficacy and a better safety profile. In gynaecology the delivery of pulsatile hormones (LHRH) is used for pregnancy induction, while transdermal oestrogens are promising in the prevention of osteoporosis. In surgical practice the use of antibiotic impregnated bone cement and antibiotic impregnated biodegradable collagens is well established. To prevent infections intravascular catheters coated with heparin or antibiotics are used. In ophthalmology the Ocusert systems provide a controlled release of different drugs in the eye. Most spectacular is the clinical introduction of the first liposomal drugs; amfotericine B and daunorubicine. Liposomal formulations of these drugs have enhanced activity and decreased toxicity compared to conventional formulations.

Criteria to assess in vivo performance of sustained release products: application to diltiazem formulations

The three classical pharmacokinetic parameters used to assess bioequivalence, AUC (total area from zero to infinity), Cmax (peak plasma concentration), and tmax (time to reach Cmax), are suitable to determine the extent and rate of absorption of immediate-release drug products. However, they may fail to evaluate the pharmacokinetic performance, particularly the rate of absorption of sustained-release (SR) formulations, which yield flat plasma curves with multiple peaks. This paper evaluates the inclusion of the following criteria for bioequivalence assessment of diltiazem SR formulations: MRT (mean arithmetic time), Cmax/AUC, peak occupancy time (POT), t(apical) (the arithmetic mean of the times associated with the concentrations within 25% of Cmax), C(apical) (the arithmetic mean of the concentration within 25% of Cmax), percent fluctuation and flatness of the curve as assessed by the coefficient of variation of the Css (steady state concentration) values obtained during a dosing interval at steady state. The above proposed criteria, as well as the classical parameters AUC, Cmax, and tmax were utilized in a recent pharmacokinetic study of a new SR product of diltiazem, Dilapress 240 (formulation A). Formulation A was analyzed following single (240 mg) and multiple (240 mg qd for 6 days) dosing at steady state (day 6) in comparison to Cardizem CD (formulation B). The bioavailability of formulation A relative to that of formulation B following single and multiple dosing was 92 +/- 28% and 90 +/- 24%, respectively. The 90% confidence intervals (Cl) over a mean AUC ratio of 89% were 78-101% (single dose, SD) and 77-101% (multiple dose, MD). following the administration of formulations A and B, identical mean values of the peak plasma concentration were obtained: 84 ng/mL (SD) and 132 ng/mL (MD). The 90% Cl over a mean Cmax ratio of 100% were 83-115% (SD) and 86-115% (MD). In the SD study, subject 8 had a relative bioavailability value of 24%, which deviated by 7.5 standard errors (SE) from the mean AUC ratio. Consequently, we repeated the single dose analysis without subject 8. The mean bioavailability data was 97 +/- 37% with a 90% Cl of 80-114% over a mean AUC ratio of 92%. ANOVA analysis did not show any formulation or period effect in all tested pharmacokinetic parameter s. On the basis of these results, these two formulations were judged to be bioequivalent. In contrast to the AUC and Cmax ratio, the 90% Cls associated with the ratio of the proposed criteria, with the exception of C(apical), did not fall within the acceptable limits. In the current study, a discrepancy was found between the above pharmacokinetic parameters, which were examined concerning their ability to detect differences in bioequivalence between SR products and the classical parameters regularly used for bioequivalence assessment. Although the parameters examined are theoretically more attractive than the single point parameters Cmax and tmax for rate of absorption assessment, their utility in bioequivalence would require further examination.