The simultaneous quantitative determination of total, 'active', acetylated and conjugated sulfonamide in biological fluids

Distribution of trimethoprim and sulphamethoxazole in blood during treatment with co-trimoxazole

Changes in the distribution of sulphamethoxazole and trimethoprim in whole blood, plasma and erythrocytes at steady-state in patients treated with cotrimoxazole have been studied. Unlike sulphamethoxazole, trimethoprim was weakly bound to erythrocytes and was partially liberated when the erythrocytes were rinsed with isotonic saline. The maximal steady-state concentration of trimethoprim in whole blood was 3 mg/l, but calculated on the basis of the concentration determined in erythrocytes it was 1.8 mg/l. Erythrocytes may be of great significance in trimethoprim distribution as carriers of a readily liberated reservoir of the drug. Acetylated sulphamethoxazole derivatives occurred in a higher percentage in erythrocytes at the maximal steady-state concentration (9.9%) than at the level (7.3%), which may help in interpreting the behaviour of this metabolite in other cells in the organism.

Simultaneous automated determination of free and total sulfisoxazole and sulfamethoxazole in plasma and urine

A fully automated method for the determination of sulfisoxazole, N4-acetylsulfisoxazole, sulfamethoxazole, and N4-acetylsulfamethoxazole in human plasma and urine was developed. Untreated plasma is analyzed by automation of dialysis, hydrolysis, color development, and quantitation. The method has a sensitivyt limit of 2 microgram/ml of plasma and has been used successfully to determine sulfonamide levels following administration of sulfoxazole and a combination drug product containing sulfamethoxazole and trimethoprim in humans. Samples are processed at the rate of 40 per hour, with a minimum of sample handling, data reduction, and materials.