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Bioavailability of terfenadine in man
Biopharmaceutics & Drug Disposition
|April 1, 1981
Summary
This study investigated terfenadine pharmacokinetics in healthy males. Results show high biotransformation, with minimal unchanged terfenadine excreted, suggesting efficient absorption and metabolism.
Area of Science:
- Pharmacology
- Drug Metabolism
- Clinical Pharmacokinetics
Background:
- Terfenadine is an antihistamine known for its efficacy.
- Understanding its absorption, distribution, metabolism, and excretion (ADME) is crucial for safe and effective use.
- Previous studies suggest significant first-pass metabolism of terfenadine.
Purpose of the Study:
- To characterize the pharmacokinetic profile of terfenadine in healthy male subjects.
- To quantify the extent of terfenadine absorption and biotransformation.
- To determine the routes of excretion for terfenadine and its metabolites.
Main Methods:
- A randomized two-way crossover study design was employed.
- Subjects received oral doses of terfenadine suspension (60mg and 180mg).
- Plasma concentrations and AUC were measured; radiolabeled terfenadine (14C) was used to track absorption and excretion via urine and feces over 12 days.
Main Results:
- Higher doses of terfenadine led to increased peak plasma concentrations and AUC.
- Approximately 99.5% of absorbed terfenadine-related material underwent biotransformation.
- Urinary excretion accounted for ~40% of the dose, fecal excretion for ~60%, with minimal unchanged terfenadine detected in feces.
Conclusions:
- Terfenadine is extensively absorbed and rapidly biotransformed, with minimal unchanged drug excreted.
- The high biotransformation rate suggests efficient hepatic metabolism.
- Excretion primarily occurs via urine and feces, with the latter likely representing metabolites rather than unabsorbed drug.
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