The effect of protein-binding on the excretion of three sulphonamide preparations in the milk of dairy cows, examined by chemical and microbiological methods.

The relationship between the protein-binding of sulphonamides and their excretion in the milk of dairy cows was studied using three preparations commercially available in Finland. After a preparations containing sulfadiazine and sulfadimidine was given intravenously to dairy cows the drugs were excreted into milk to a greater extent than in the case of sulfamethoxypyridazine and especially of sulfaphenazole given similarly. An inverse relationship was found between the degree of protein-binding in the serum and the excretion into milk. The antimicrobially active concentrations of sulphonamides in serum and milk persisted for less than 24 hours when the doses recommended by the manufacturers were used. From a pharmacological point of view the sulfadiazine-sulfadimidine combination seems to be the drug of choice. Although no traces of sulphonamides were detected 48 hours after the dosing, the question of milk residues could not be answered because the minimum detection level of the methods used in the study was approximately 1 microgram/ml. The IDF standard method for the detection of penicillin in milk is not suitable for the detection of sulphonamide residues in milk.