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

Following intravenous (i.v.) or intramuscular (i.m.) administration of sulphadimidine (SDM), the pharmacokinetics of SDM and N4-acetylsulphadimidine (N4-SDM) were studied in plasma of calves from the first day of life to the age of about 6 months. An obvious age dependency was observed for the elimination half-life (t1/2) of SDM: the first day of life the t1/2 ranged between 13.5 and 17 h, and decreased in approximately 3 weeks to 4-6 h and remained constant from this time. The metabolite N4-SDM, as a percentage of the total concentration of the sulphonamide measured in plasma of neonatal calves, ranged between 21.6 and 25.5% at the first day of life, declined in 3 weeks to approximately 12.8%, and at 5 till 9 weeks the final percentage was about 6.8%. Following administration of N4-SDM, the elimination half-life of N4-SDM was 3 h in an 8-day-old calf declined to 1.4-1.7 h in 4-week-old calves, and was 0.9 h in calves older than 11 weeks. 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 sulphonamide plasma concentration. This value was age-related. The total body clearance of N4-SDM was three- to five-fold higher than that of SDM.