Serum chloramphenicol concentrations in preruminant calves: a comparison of two formulations dosed orally

Serum concentrations of chloramphenicol were determined after oral doses (55 mg/kg body weight) were administered to 7-9 day old Holstein-Friesian calves. Chloramphenicol in an oral solution produced greater serum concentrations than did an equivalent dose of chloramphenicol in capsules (P less than 0.005). A second dose of each formulation administered 12 h after the first dose elevated serum chloramphenicol concentrations significantly (P less than 0.001). The average serum chloramphenicol concentration exceeded 5 micrograms/ml of serum 1 h after administration of the solution compared with 4 h for the capsules. Average serum chloramphenicol concentration was greater than 5 micrograms/ml for at least 12 h after the dose was administered for both formulations. Of the eight calves receiving repeat doses of chloramphenicol, seven (87.5%) developed diarrhea in 76 +/- 8.6 h. Six of the eight calves (75%) died during or shortly after the period of chloramphenicol administration.