Pharmacokinetics of co-trimoxazole and co-tetroxazine in geriatric patients.

Following a single dose of co-trimoxazole or co-tetroxazine, the plasma and urine levels of intact trimethoprim (TMP) and sulphamethoxazole (SMZ) and of tetroxoprim and sulphadiazine (SDZ) were determined in six geriatric patients in a cross-over design by high pressure liquid chromatography. The pharmacokinetic analysis showed a plasma elimination half-life in the terminal phase of 10.39 h for TMP, 11.79 h for SMZ, 6.55 h for TXP and 10.46 h for SDZ. The resulting distribution volumes Vd beta and total plasma clearance values corresponded with the data obtained in young patients or volunteers. Recovery in urine, measured for up to 96 h, was 49.2% (TMP), 19.8% (SMZ), 57.03% (TXP) and 61.1% (SDZ). In contrast to young volunteers, geriatric patients experienced a slight prolongation of renal excretion for both sulphonamides. In this group of patients the renal clearance was 2.42 ml/min for SMZ and 10.7 ml/min for SDZ.