Pharmacokinetics of sulfisoxazole in young and elderly subjects

The pharmacokinetics of sulfisoxazole was studied in 6 elderly (age 63-75 years) and 7 young (age 22-37 years) healthy nonsmoking volunteers following the oral administration of 2 g of Gantrisin. The plasma levels of sulfisoxazole obtained in the postabsorption phase were higher in the elderly subjects. There was no significant variation between the two groups of volunteers in the absorption rate constant, Cmax, bioavailability, the fraction of the dose of sulfisoxazole excreted unchanged, the area under the plasma curve of the N4-acetyl conjugate formed, and in the apparent volume of distribution of the drug. The tmax value and plasma half-life of sulfisoxazole were significantly longer, and the total body and renal clearances of the drug decreased in the elderly subjects. Diminished renal function as estimated by the creatinine clearance and urinary flow may explain the slower elimination of sulfisoxazole in the elderly subjects. Therefore, advancing age should be considered as a factor in the adjustment of sulfisoxazole dosage.