Bioavailability of chlorothiazide tablets in humans

Area of Science:

• Pharmacokinetics
• Drug Absorption
• Bioavailability Studies

Background:

• Chlorothiazide is a widely prescribed thiazide diuretic.
• Evaluating the bioavailability of generic drug products is crucial for therapeutic equivalence.
• Urinary excretion is a common method for assessing drug absorption after oral administration.

Purpose of the Study:

• To assess the urinary excretion bioavailability of three 250-mg and three 500-mg chlorothiazide tablet formulations.
• To identify potential differences in drug absorption between various chlorothiazide products.
• To investigate the relationship between urinary excretion data and dissolution rates.

Main Methods:

• A crossover bioavailability study involving 12 healthy male subjects.
• Administration of single oral doses of 250-mg and 500-mg chlorothiazide tablets.
• Collection of urine samples at multiple time points (1-24 hours) post-dose.
• Statistical analysis of cumulative urinary drug recovery, excretion rate, and time to maximum excretion rate.

Main Results:

• No statistically significant differences were observed among the three 250-mg chlorothiazide tablet formulations.
• One 500-mg chlorothiazide product exhibited significantly lower urinary drug recovery (p < 0.05) compared to the other two 500-mg products.
• Overall mean urinary recovery ranged from 11% to 20%, indicating generally poor oral absorption of chlorothiazide.
• Correlation between urinary excretion data and dissolution rates was unsuccessful.

Conclusions:

• While 250-mg chlorothiazide tablets demonstrated comparable bioavailability, variability exists among 500-mg formulations.
• The low overall drug recovery suggests limited oral absorption of chlorothiazide, irrespective of the product tested.
• Further investigation may be needed to understand the factors influencing chlorothiazide absorption and the lack of correlation with dissolution.