Sulfadimidine curves

Franek et al developed an immunoassay for sulfadimidine, but they found that milk samples required dilution (1 100), and tissues required dilutions of 1 200 to 1 4000. The LOD was 0.02 pg kg from the buffer calibration curve with the IC50 at 0.15 pgkg The assay measured levels in milk from 10 to 100 pgkg with satisfactory precision. In swine muscle, kidney, and liver samples, levels from 20 to 500 pg kg could be measured when 2 g of tissue were homogenized with 20 mL of buffer and then diluted 1 20. 

In the horse, hydroxylation is more important than acetylation as a metabolic pathway, with hydroxylation at the 5 position being dominant over hydroxylation of the 6-methyl group. Low percentages of metabolites are present in plasma, for N -SDM, 0.6 to 0.9 % for SCH2OH, 0.38 to 0.71 % and for SOH, 0.38 to 6.7 %. The plasma concentration-time curves of the metabolites run parallel to that of SDM. The elimination half-life of sulfadimidine varies between 5 and 14 h. The main metabolite in urine, accounting for 50 % of the drugs present (Table III), is the SOH and its glucuronide. 

Figure 3. Plasma concentration-time curves of sulfadimidine (SDM), and its 6-methylhydroxy (CHoOH), 5-hydroxy (SOH) and its glucuronide (SOH N -acetyl CN ) and unknown (X) metabolites in a cow after an intravenous dose of 200 mg/kg sulfadimidine.

Figure 9. Drug depletion time curves of sulfadimidine (SDM), and its metabolites (N, CH2OH) in the egg albumen and egg yolk during and after cessation of the administration of 100 mg SDM/kg during 5 days.

Laying-hens eliminate sulfadimidine rapidly by metabolic pathways including hydroxylation and acetylation. Following intravenous SDM administration, a biphasic elimination-time curve was noticed 10.2 + 3.3 H). Figure 8 shows the plasma disposition of SDM and its metabolites following an oral SDM bolus administration once daily of 100 mg/kg to a chicken. The percentage of N -SDM in plasma is the highest (Table I). Within 3 days of termination of the SDM therapy, plasma concentrations of SDM and its metabolites falls rapidly below the detection limit of the HPLC method (0.02 /ig/ml). 

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