Comparative bioavailability of two immediate release tablets of cisapride in healthy volunteers

Pediatric pharmacokinetics: human development and drug disposition

Human development is described by the various anatomic and physiologic changes that occur as the single-celled zygote matures into an adult human being. Concomitant with bodily maturation are changes in the complex interactions between pharmacologic agents and the biologic matrix that is the human body. Profound changes in the manner by which drugs traverse the body during development can have significant implications in drug efficacy and toxicity. Although not a replacement for well-conducted, pediatric, pharmacokinetic studies, an understanding of developmental biology and the mechanisms for drug disposition invariably assists the pediatric clinician with the judicious use of medications in children.

High performance liquid chromatographic determination, pharmacokinetic and comparative bioavailability studies of cisapride

A sensitive and specific reversed phase HPLC method was developed to quantitate plasma levels of cisapride in order to conduct comparative bioavailability studies. The drug and internal standard was extracted from plasma with heptane-isoamyl alcohol (95:5 v/v) and back extracted with sulfuric acid. The acidic layer was then re-extracted with the same extracting solvent. The separated organic layer was evaporated to dryness under nitrogen and the residue reconstituted with acetonitrile. Analysis was performed on a C-8 Sil-X-10 HPLC column, with a mobile phase of acetonitrile, water, and triethylamine (75:25:0.01) and UV detection at 215 nm. The standard curve covering the concentration range 5-160 ng/ml was linear (r(2)=0.9992), relative errors were within +/-10% and the CV% ranged from 1.34 to 11.82. The in vivo study was carried out in 12 healthy volunteers according to a single dose, two-sequence, cross over randomized design. The bioavailability was compared using the total area under the plasma level versus time curve (AUC(0-34,) AUC(0- infinity )), peak plasma concentration (C(max)) and time to C(max) (T(max)). No statistically significant difference was found between the AUC(0- infinity ) or C(max) values of the test (cisapride) and reference (Propulsid). It was, therefore, concluded that the generic cisapride was bioequivalent with the innovator formulation.

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.