The bioavailability and pharmacokinetics of slow release nifedipine during chronic dosing in volunteers

Mechanistic Framework to Predict Maternal-Placental-Fetal Pharmacokinetics of Nifedipine Employing Physiologically Based Pharmacokinetic Modeling Approach

Nifedipine is used for treating mild to severe hypertension and preventing preterm labor in pregnant women. Nevertheless, concerns about nifedipine fetal exposure and safety are always raised. The aim of this study was to develop and validate a maternal-placental-fetal nifedipine physiologically based pharmacokinetic (PBPK) model and apply the model to predict maternal, placental, and fetal exposure to nifedipine at different pregnancy stages. A nifedipine PBPK model was verified with nonpregnant data and extended to the pregnant population after the inclusion of the fetoplacental multicompartment model that accounts for the placental tissue and different fetal organs within the Simcyp Simulator version 22. Model parametrization involved scaling nifedipine transplacental clearance based on Caco-2 permeability, and fetal hepatic clearance was obtained from in vitro to in vivo extrapolation encompassing cytochrome P450 3A7 and 3A4 activities. Predicted concentration profiles were compared with in vivo observations and the transplacental transfer results were evaluated using 2-fold criteria. The PBPK model predicted a mean cord-to-maternal plasma ratio of 0.98 (range, 0.86-1.06) at term, which agrees with experimental observations of 0.78 (range, 0.59-0.93). Predicted nifedipine exposure was 1.4-, 2.0-, and 3.0-fold lower at 15, 27, and 39 weeks of gestation when compared with nonpregnant exposure, respectively. This innovative PBPK model can be applied to support maternal and fetal safety assessment for nifedipine at various stages of pregnancy.

In vitro-in vivo extrapolation of metabolic clearance using human liver microsomes: factors showing variability and their normalization

In vitro-in vivo extrapolation (IVIVE) using human liver microsomes has been widely used to predict metabolic clearance, but some of the factors used in the process of prediction show variability for the same compound: notably, microsomal intrinsic clearance values corrected by the unbound fraction (CL_{int, u}), physiological parameters used for scale-up, and the source of in vivo clearance data.The purpose of this study was to assess the correlation between in vitro and in vivo CL_int with a focus on factors showing variability using four cytochrome P450 (CYP)3A substrates.We surveyed in vivo clearance values in literature and also determined the microsomal CL_{int, u} values. A scaling factor (SF_direct) was defined as in vivo CL_int divided by the microsomal CL_{int, u}, which ranged from 1190 to 2310 (mg protein per kg body weight). The application of a mean SF_direct of 1600 (mg protein per kg body weight) and further normalization by the microsomal CL_{int, u} values of midazolam, the most commonly used substrate, resulted in improved prediction accuracy for CL_{int, u} values from various microsomal batches.The results suggest the normalization of variability might be useful for predicting the in vivo CL_int.

Quantitation of nifedipine in human plasma by on-line solid-phase extraction and high-performance liquid chromatography

An analytical methodology for nifedipine quantitation in plasma by on-line solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) is described. The SPE cartridges contain C2 and the analytes nifedipine and nitrendipine (internal standard) are separated on a C18 column with a mobile phase consisting of acetonitrile-13 mM phosphate buffer pH 7 (65:35, v/v) followed by UV detection at 338 nm. Validation of the method demonstrated good recoveries (>90%), sensitivity (limit of quantification, 2 ng/ml), based on a 500 microl sample volume, accuracy and precision (<5.5% in concentrations greater than the limit of quantitation). This methodology has been used for bioequivalence studies.

The nifedipine gastrointestinal therapeutic system (GITS). Evaluation of pharmaceutical, pharmacokinetic and pharmacological properties

Nifedipine is a short-acting calcium antagonist formulated into several different oral preparations, each of which offers a distinct drug release profile. Of these, the nifedipine gastrointestinal therapeutic system (GITS) affords (rate)-controlled-release (CR) and once-daily administration. Although it is recognised that CR drug formulations may enhance the treatment compliance of patients by reducing the number of daily doses, there are several pharmaceutical, pharmacokinetic and pharmacological considerations which may influence the ultimate selection of a particular dosage form. The formulation design of the nifedipine GITS involves an osmotic pump process which provides approximately zero-order delivery of the drug. This mechanism serves to prevent the possibility of dose dumping, but more importantly allows for maintenance of the relatively constant plasma drug concentrations assumed necessary to maintain smooth control of blood pressure. The pharmacokinetic characteristics of the nifedipine GITS have been evaluated in both single- and multiple-dose studies. The GITS formulation provides drug concentrations which reach a plateau within 6 hours after administration of a single dose, and continue at that concentration until at least 24 hours after administration. In this way large fluctuations in plasma drug concentrations are avoided, which may improve the efficacy and tolerability of the drug. Although a trend showing a small increase in the 24-hour plasma nifedipine concentrations has been observed by our group from some single-dose studies, it does not appear to be clinically relevant. One potentially important disadvantage of the GITS compared with 'naturally' long-acting agents is that the 'intrinsic' pharmacokinetic properties of nifedipine may be exposed in poorly compliant patients, leading to extended periods of subtherapeutic drug concentrations. Drug delivery by the nifedipine GITS is unaffected by changes in pH and gastrointestinal (GI) motility, but the rate of drug release can increase slightly with food intake (although absolute bioavailability remains unchanged). No studies have been conducted to determine the average GI transit time of this particular dosage form, but it is possible that inadequate retention may occur in some patients, perhaps leading to less optimal clinical outcomes. For example, the median GI transit time for both oxprenolol and metoprolol Oros drug delivery systems has been reported as 27.4 hours, with individual times ranging from 5.1 to 58.3 hours. The possibility of inadequate GI retention of the nifedipine GITS is perhaps more likely in patients who have pre-existing GI motility disorders or who are taking other medications that enhance GI motility. The interaction between grapefruit juice and nifedipine is interesting, considering that the exact mechanism involved has yet to be determined. Nonetheless, inhibition of presystemic metabolic processes (probably involving liver enzymes but possibly also enzymes contained within the wall of the small intestine) is likely to be a factor in the increased bioavailability of nifedipine observed in individuals coingesting grapefruit juice. Thus, potential nifedipine formulation differences with respect to the degree of interaction with grapefruit juice may occur if a significant degree of extrahepatic metabolism is involved. The majority of clinical trials with the nifedipine GITS have assessed its efficacy in patients with mild-to-moderate essential hypertension, and have found it to be at least equivalent to other dosage forms of the drug. Since there is limited information available directly comparing the efficacy and adverse effects of the different types of nifedipine formulation, little attention has been focused on this subject. However, modifying the rate and duration of nifedipine release may profoundly affect the clinical performance of this drug. A slower rate of intravenous nifedipine infusion has been shown to reduce the incide

Pharmacokinetic profile of nifedipine GITS in hypertensive patients with chronic renal impairment

25 hypertensive patients with normal or impaired renal function underwent pharmacokinetic and safety studies after single and multiple dose administration of nifedipine GITS (Gastro-Intestinal Therapeutic System) 60mg tablets. Complete pharmacokinetic data were obtained from 23 of these patients. Blood pressure and heart rate changes were compatible with the known properties of the drug. Impaired renal function did not affect the maximum plasma concentrations or bioavailability of nifedipine after single or multiple dose administration of nifedipine GITS, nor was there any evidence of excessive drug accumulation in the presence of renal impairment.

Pharmacokinetics of oral nifedipine in different populations

Nifedipine disposition varies among populations. Reports on oral nifedipine pharmacokinetics show that peak plasma levels and AUC values are higher in Mexican and Japanese than in European and North American subjects. Increased nifedipine bioavailability in the nonwhite populations is likely due to nutritional habits. Certain flavonoids that inhibit the first-pass metabolism of dihydropyridines are present in the diets of both Mexican and Japanese. Differences in phenotypes may play a role in interethnic variability.

Analysis of nifedipine and its pyridine metabolite dehydronifedipine in blood and plasma: review and improved high-performance liquid chromatographic methodology

A reversed-phase HPLC method is described for the simultaneous determination of nifedipine and its primary pyridine metabolite dehydronifedipine in blood and plasma, that involves UV detection and neutral (blood) or alkaline (plasma) extraction. The limit of reliable determination is found to be 3 ng ml-1 with an inter-assay RSD of below 11%. In the presence of haemoglobin, nifedipine is unstable at pH greater than 10, necessitating neutral extraction for the measurement of nifedipine in haemolysed blood. Published methods for analysis of nifedipine are reviewed, emphasizing the lack of specificity and sensitivity which render many of them unsuitable for the investigation of nifedipine disposition in man.

The interaction between i.v. theophylline and chronic oral dosing with slow release nifedipine in volunteers

Eight healthy volunteers received a 5 min i.v. infusion of lysine theophylline, equivalent to 197 mg anhydrous theophylline, both before (day 1) and during (day 5) steady state chronic oral dosing with slow release nifedipine 20 mg 12 hourly. A theophylline pharmacokinetic profile was performed on day 1 and day 5 and a nifedipine pharmacokinetic profile was performed on day 4 and day 5. The greatest difference in serum theophylline concentrations was seen at the first sampling time (5 min after completion of the infusion) with a mean concentration of 9.9 mg l-1 during nifedipine administration and 14.6 mg l-1 with theophylline alone. Thereafter, the difference fell to approximately 1 mg l-1 until 6 h when they became almost identical. Repeated measures analysis of variance using the theophylline serum concentrations at each of ten time points over 8 h as the repeated measures showed a small but significant effect of nifedipine (F(1,151) = 7.0, P less than 0.01) on serum theophylline concentrations. Mean volume of distribution (V) rose from 0.33 +/- 0.07 to 0.39 +/- 0.06 1 kg-1 corrected body weight (CBW) in the presence of nifedipine (t = 2.23, P = 0.052). Theophylline clearance, area under the curve to 8 h AUC (0-8), area under the curve to infinity AUC (0-infinity) and elimination half-life (t1/2) did not change appreciably. No statistically significant changes in nifedipine pharmacokinetics occurred in the presence of theophylline.