Bioavailability of regular and controlled-release chlorpheniramine products

Area of Science:

• Pharmacokinetics
• Drug bioavailability
• Pharmaceutical formulation

Background:

• Chlorpheniramine is a widely used antihistamine.
• Understanding the bioavailability of different chlorpheniramine formulations is crucial for effective therapeutic use.
• Controlled-release formulations aim to provide sustained drug levels, but their efficacy can vary.

Purpose of the Study:

• To compare the bioavailability of chlorpheniramine from regular-release and controlled-release oral dosage forms.
• To evaluate pharmacokinetic parameters including Cmax, time to peak concentration, and AUC.
• To assess the impact of formulation on the absorption profile of chlorpheniramine.

Main Methods:

• A 5-way crossover study involving 15 human subjects.
• Administration of single oral doses of various chlorpheniramine products (capsules, tablets, syrups).
• Plasma chlorpheniramine levels were measured using HPLC, with pharmacokinetic analysis based on a two-compartment open model.

Main Results:

• The average plasma elimination half-life of chlorpheniramine was approximately 18.3 hours.
• Controlled-release products achieved higher Cmax than 4-mg syrup but lower than two 4-mg tablets.
• Peak plasma levels were reached later with controlled-release products compared to syrups, and AUC data indicated incomplete bioavailability.

Conclusions:

• Controlled-release chlorpheniramine formulations successfully extended the absorption time.
• However, this prolonged absorption came at the cost of reduced overall drug bioavailability.
• The bioavailability of controlled-release chlorpheniramine was not equivalent to the same total dose of regular-release products.