Bioavailability of chlorothiazide from 50, 100, and 250 MG solution doses

The bioavailability of chlorothiazide was examined following single oral solution doses to eight healthy male volunteers. Drug was administered in 250 ml of water after overnight fast. Bioavailability was determined by measuring 72 h urinary recovery of unchanged drug. Mean urinary recovery from 50, 100, and 250 mg doses was, respectively, 28.3, 47.0 and 83.3 mg, representing 56.4, 47.0, and 33.3 per cent of the administered dose. The correlation coefficient between dose size and percentage recovery was -0.662. These results add support to previous suggestions that the absorption of chlorothiazide from the gastrointestinal tract is saturable, and that the availability of chlorothiazide may be similar to that of hydrochlorothiazide when these compounds are administered in the same dosage range.