Acetylation of sulfisoxazole by isolated perfused rat kidney

Pharmacokinetics of sulfisoxazole in renal transplant patients

We studied the elimination of sulfisoxazole in eight renal transplant patients. The patients received sulfisoxazole prophylactically for urinary tract infection commencing 7 days postoperatively. The renal elimination of sulfisoxazole (unbound renal clearance) was decreased in this patient population and was highly correlated with creatinine clearance. The unbound metabolic clearance and apparent unbound formation clearance of N4-acetyl sulfisoxazole did not differ from values found in healthy volunteers. The protein binding was marginally lower in this patient population than in healthy subjects after a single dose. The reduced binding was compatible with a reduced albumin concentration. In contrast to the situation for healthy subjects, the binding of sulfisoxazole decreased upon multiple dosing. This is probably due to a relatively higher sulfisoxazole and N4-acetyl sulfisoxazole-to-albumin ratio in this patient population than in healthy subjects. No complications of sulfisoxazole therapy were seen, although in three subjects concentration of the N4-acetyl sulfisoxazole in urine exceeded its theoretical solubility on a few occasions.

Cimetidine-procainamide pharmacokinetic interaction in man: evidence of competition for tubular secretion of basic drugs

The hypothesis that basic drugs can compete for active tubular secretion by the kidney was tested in six healthy volunteers by comparing the single dose pharmacokinetics of oral procainamide before and during a daily dose of cimetidine. The area under the procainamide plasma concentration-time curve was increased by cimetidine by an average of 35% from 27.0 +/- 0.3 micrograms/ml X h to 36.5 +/- 3.4 micrograms/ml X h. The elimination half-life increased from an harmonic mean of 2.92 to 3.68 h. The renal clearance of procainamide was reduced by cimetidine from 347 +/- 46 ml/min to 196 +/- 11 ml/min. All these results were statistically significant (p less than 0.016). The area under the plasma concentration-time curve for n-acetylprocainamide was increased by a mean of 25% by cimetidine due to a significant (p less than 0.016) reduction in renal clearance from 258 +/- 60 ml/min to 197 +/- 59 ml/min. The data suggests that cimetidine inhibits the tubular secretion of both procainamide and n-acetylprocainamide, and, if so, represents the first documented evidence for this type of drug interaction in man. The clinical implications from this study necessitate dosage adjustments of procainamide in patients being concomitantly treated with cimetidine. The interaction is pertinent not only for basic drugs that are cleared by the kidney, but also for metabolites of basic drugs and endogenous substances which require active transport into the lumen of the proximal tubule of the kidney for their elimination.

Variability of plasma hydralazine concentrations in male hypertensive patients

The efficacy and toxicity of hydralazine differ widely among individual patients, possibly because of different sensitivities to drug effect or as a reflection of pharmacokinetic differences. Therefore, the variability in plasma hydralazine concentrations after single intravenous and single and multiple oral doses was studied in 9 male hypertensive patients. After an intravenous dose of 0.3 mg/kg the area under the plasma concentration time curve (AUC) varied over less than a twofold range 17.5-29.5 muM-minute. However, after a single oral dose, 1 mg/kg, and after at least the fifth dose of a regimen consisting of 1 mg/kg given every 12 hours, there were much wider variations in AUC values: 4.0-30.4 and 3.2-38.5 muM-minute, respectively. Similar ranges in peak hydralazine concentration, Cp, were also noted, 0.12-1.31 muM after single oral dose and 0.10-1.39 muM after the multiple dose regimen. A significant portion of the observed interpatient variability could be explained by differences in acetylation ability. The AUC and Cp values for both the single and multiple oral doses were significantly lower (P less than 0.001) in rapid than in slow acetylators. Therefore, determining the acetylation ability of patients requiring hydralazine may help to optimize therapeutic benefit and minimize toxicity.