Related Experiment Video
Updated: Aug 14, 2026
07:02
A Computerized Test Battery to Study Pharmacodynamic Effects on the Central Nervous System of Cholinergic Drugs in Early Phase Drug Development
Published on: February 11, 2019
Bioavailability of controlled release carbamazepine estimated by mixed effect modelling
1Department of Pharmacology, University of Durban-Westville, Republic of South Africa.
European Journal of Clinical Pharmacology
|January 1, 1993
Summary
This study compared carbamazepine (T) and controlled-release carbamazepine (TCR) absorption using nonlinear mixed-effect modeling. Different absorption rates significantly improved the model fit for both dosage forms.
Area of Science:
- Pharmacokinetics and Pharmacodynamics
- Drug Absorption and Bioavailability
- Nonlinear Mixed-Effects Modeling
Background:
- Carbamazepine is a widely used antiepileptic drug.
- Understanding absorption differences between conventional (T) and controlled-release (TCR) formulations is crucial for optimizing therapy.
- Nonlinear mixed-effects modeling (NONMEM) is a powerful tool for analyzing complex pharmacokinetic data.
Purpose of the Study:
- To compare the absorption properties of conventional carbamazepine (T) and controlled-release carbamazepine (TCR).
- To evaluate the influence of pharmacokinetic parameters, including absorption rate (ka) and relative bioavailability (f), on model fit.
- To identify key determinants of carbamazepine pharmacokinetics, such as body weight.
Main Methods:
- Utilized a nonlinear mixed-effect model (NONMEM) for pharmacokinetic analysis.
- Analyzed plasma carbamazepine concentration data from 13 patients in an open, steady-state, crossover bioavailability study (494 measurements).
- Employed a one-compartment open model with first-order absorption and elimination, assessing goodness-of-fit via the objective function.
Main Results:
- Body weight significantly influenced carbamazepine clearance (CL) but not volume of distribution (V).
- Incorporating distinct absorption rates (ka) for T and TCR significantly improved the model's objective function and reduced inter-individual variability.
- While adding relative bioavailability (f) for TCR offered statistical improvement, it led to unrealistic V values; fixing V allowed accurate estimation of f.
Conclusions:
- Absorption rates (ka) differ significantly between conventional and controlled-release carbamazepine formulations.
- Nonlinear mixed-effects modeling effectively differentiates pharmacokinetic profiles of different carbamazepine dosage forms.
- Accurate pharmacokinetic modeling requires careful parameterization to avoid confounding effects and ensure realistic parameter estimates.
Related Concept Videos
01:13Bioavailability: Overview
Bioavailability refers to the proportion of an unaltered drug that, after administration, enters the systemic circulation and can be distributed to the desired action site. Factors such as gastrointestinal (GI) absorption and liver biotransformation influence the bioavailability of a drug when it is administered orally. When a drug is administered intravenously, it enters the systemic circulation directly; by definition, its bioavailability is assumed to be 100%. The bioavailability of an...
01:14Time Course of Drug Effect
The progression of a drug's impact can be analyzed by examining both the concentration-time course and the effect-time course. The concentration-time course is determined by the drug's half-life and is influenced by factors such as its pharmacokinetics, including absorption, distribution, metabolism, and elimination. The effect of the drug is often related to its concentration in the plasma and is calculated using the maximum drug effect and the plasma concentration that generates 50 percent of...
01:22Bioavailability: Influencing Factors
Bioavailability refers to the extent and rate at which a drug reaches systemic circulation in its active form. Extent refers to the amount of the drug that makes it into circulation, while rate is the speed at which it enters circulation. It is influenced by several factors critical for optimizing drug formulations, dosing regimens, and therapeutic outcomes.Physicochemical properties of drugs and formulationsThe solubility, stability, and dissolution rate of a drug significantly impact its...
01:11Bioavailability Study Design: Single Versus Multiple Dose Studies
Bioavailability studies are essential for understanding how a drug is absorbed, distributed, metabolized, and excreted in the body. These studies assess the extent and rate at which the active pharmaceutical agent becomes available at the site of action. The design of bioavailability studies can involve single-dose or multiple-dose regimens, each with distinct advantages and limitations.Single-dose studies are the preferred approach due to their simplicity and reduced drug exposure for...
01:20Measurement of Bioavailability: Pharmacodynamic Methods
Pharmacodynamic methods provide insights into a drug's effects on physiological processes over time and play a crucial role in understanding bioavailability and therapeutic efficacy. These methods can be broadly classified into acute pharmacological and therapeutic response approaches, each with distinct mechanisms and applications.The acute pharmacological response method directly correlates a drug's physiological effects, such as ECG or pupil diameter changes, to its time course in the body.
01:30Modified-Release Drug Delivery Systems: Bioavailability
Modified-release (MR) dosage forms are designed to extend drug release over time, thereby maintaining stable plasma concentrations and reducing dosing frequency. However, their bioavailability is typically below 100% due to incomplete drug release and presystemic metabolism, and limitations in drug permeability across the gastrointestinal epithelium, all of which can restrict the fraction of the drug reaching systemic circulation. Consequently, studying the in vivo bioavailability of MR...