Fluorometric determination of hydroflumethiazide in human plasma and urine after its oral administration

A spectrofluorometric method for determination of hydroflumethiazide in human plasma and urine has been developed. The limit of detection was 10 ng/ml plasma and 100 ng/ml urine. The plasma concentration of hydroflumethiazide was determined for 9-11 hours and excretion in urine for 24-37 hrs after oral administration of about 1 mg/kg body weight to 7 subjects. Plasma half life in healthy subjects was 1.9-2.1 h, and 2.7-8.6 h in patients during the period 4-9 hrs after dosing. Cumulative excretion in urine was 67-79% of the dose during 31-37 hrs in 6 subjects; one patient with renal disease was found to excrete only 25.8% of dose during 24 hours. Renal clearance of hydroflumethiazide was higher in the healthy subjects (0.29-0.44 1 h-1 kg-1) than in the patients (0.040-0.15 1 h-1 kg-1). Plasma half life of hydroflumethiazide was not closely correlated with renal clearance of the drug, which suggests that other factors may play a role in determining plasma half life.