Penicillin Blood and Milk Concentrations in the Normal Cow Following Parenteral Administration

Abstract

A cow weighing 1,300 lb. and milking 55 lb. daily received 16,250,000 U. of amorphous penicillin Na (Expt. 1). A cow weighing 1,380 lb. and milking 35 lb. daily received 17.250,000 U. of crystalline penicillin G Na (Expt. 2). In each case, the penicillin was reconstituted in 1 ml. of saline for each 200,000 U. The drug was given subcut. at the rate of 5,000 U/lb. for the 1st dose and 2,500 U./lb. for 3 later doses at 6-hr. intervals. Blood and milk samples were taken 15 min. and 1 hr. after the 1st dose, and every hr. thereafter, for 30 hrs. The cows were milked out before the first injn. and at 12-hr, intervals thereafter. Serum assays were made by the method of Chandler, Price, and Randall (1945), milk assays by a modification of the Bacillus subtilis cup-plate method of Foster and Woodruff (1944). A level of 8 U./ml. of blood was recorded 15 min. after the 1st dose, and this decreased steadily to 0.5 U. in 5 hrs. After each later dose, the level rose again, reaching 2, 2, and 1 U. at the 7th, 14th, and 19th hrs., respectively. At the 29th and 30th hrs., there was less than 0.03 U./ml. present in the blood. The milk level 15 min. after the 1st dose was less than 0.05 U/ml. This rose steadily to 0.84 U/ml. at the 5th hr., decreased slightly, and rose again after the 2d dose to 0.78 U. at the 8th hr. There was a very slight increase after each injn. of penicillin. A milk level of 0.06 U. was still present at 30 hrs. In Expt. 2, a level of 4 U./ml. of blood was recorded at 15 min. and persisted for 1 hr. The blood concns. decreased to about 0.5 U. or less within each 6-hr. period. After each subsequent dose, the levels rose to slightly less than the highest level recorded. No penicillin could be measured in the blood after 29 hrs. The milk level curve was similar to that of the first expt., with a high of 0.53 U. at 15 hrs. and 0.1 U. at 30 hrs. The expts. show that measurable amts. of penicillin in milk are not likely to be found unless blood concns. are high and persistent.