Pharmacokinetics, renal clearance, tissue distribution, and residue aspects of sulphadimidine and its N4‐acetyl metabolite in pigs

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Abstract
Pharmacokinetics and tissue distribution experiments were conducted in pigs to which sulphadimidine (SDM) was administered intravenously, orally, and intramuscularly at a dosage of 20 mg SDM/kg. SDM was acetylated extensively, but neither hydroxy metabolites nor their derivatives could be detected in plasma, edible tissues or urine. Following i.v. and two oral routes of administration, the N4‐acetylsulphadimidine (N4‐SDM) concentration‐time curve runs parallel to that of SDM. The percentage of N4‐SDM in plasma was in the range between 7 and 13.5% of the total sulphonamide concentration. The bioavailability of SDM administered in a drench was 88.9 ± 5.4 % and administered mixed with pelleted feed for 3 consecutive days it was 48.0 ± 11.5 %. The renal clearance of unbound SDM, which was urine flow related, was 1/7 of that of creatinine, indicating reabsorption of the parent drug. The unbound N4SDM was eliminated three times faster than creatinine, indicating that tubular secretion was the predominant mechanism of excretion. After i.v. administration, 51.9 % of the administered dose was recovered in urine within 72 h p.i., one quarter of which as SDM and three quarters as N4‐SDM. Tissue distribution data obtained at 26, 74, 168, and 218 h after i.m. injection revealed that the highest SDM concentration was found in plasma. The SDM concentration in muscle, liver, and kidney ranged from one third to one fifth of that in plasma. The N4‐SDM formed a minor part of the sulphonamide content in edible tissues, in which the SDM as well as the N4‐SDM concentration parallelled the plasma concentrations. Negative results obtained with a semi‐quantitative bioassay method, based on monitoring of urine or plasma, revealed that the SDM concentration levels in edible tissues were in that case below 0. 1μ/g tissue.