Pharmacokinetics of sodium cephapirin in lactating dairy cows.

Sodium cephapirin was administered (10 mg/kg of body weight, IM) at 8-hour intervals in 4 consecutive doses to each of 6 lactating dairy cows. Blood, normal milk, mastitic milk, urine, and endometrial tissue samples were collected serially. Mean peak cephapirin concentrations in serum were 13.3 micrograms/ml 10 minutes after the 1st injection and were 15.8 micrograms/ml 20 minutes after the 4th injection (post[initial]injection hour [PIH] 24.33). The overall elimination rate constant value was 0.66/h and plasma clearance was 760 ml/h/kg. Mean peak cephapirin concentration in normal milk was 0.11 microgram/ml at PIH 2 and mean peak cephapirin concentration in mastitic milk was 0.18 microgram/ml at PIH 4. Cephapirin was not detected in the endometrium. The highest concentration of cephapirin in urine was 452 micrograms/ml, 2 hours after the 4th dose (PIH 26).