Effect of age on the acetylation and deacetylation reactions of sulphadimidine and N4- acetylsulphadimidine in calves

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Abstract
Following i.v. or i.m. administration of sulfadimidine (SDM), the pharmacokinetics of SDM and N4-acetylsulfadimidine (N4-SDM) were studied in plasma of calves from the 1st day of life to the age of .apprx. 6 mo. An obvious age dependency was observed for the elimination half-life (t1/2) of SDM: on the 1st day of life, the t1/2 ranged between 13.5-17 h; it decreased in .apprx. 3 wk to 4-6 h and remained constant from that time. The metabolite N4-SDM, as a percentage of the total concentration of the SDM measured in plasma of neonatal calves, ranged between 21.6-25.5% at the first day of life, declined in 3 wk to .apprx. 12.8%; at 5-9 wk, the percentage was .apprx. 6.8%. Following administration of N4-SDM, the t1/2 of N4-SDM, 3 h in an 8 day old calf, declined to 1.4-1.7 h in 4 wk old calves, and was 0.9 h in calves older than 11 wk. The percentage of SDM (a metabolite of N4-SDM) in plasma increased with time after injection from 5.5 to 62.8% of the total SDM plasma concentration. This value was age-related. The total body clearance of N4-SDM was 3- to 5-fold higher than that of SDM.