Pharmacological aspects of chloramphenicol administration by the intramammary route to lactating dairy cows

Abstract

Concentrations of chloramphenicol (CM) were determined, by microbiological assay, in the milk and blood serum of 17 culled dairy cows after intramammary infusion of an approved parenteral CM product (Gloveticol®) and in the milk of 16 lactating cows after treatment with two approved CM products for intramammary infusion, at dosages ranging from 1 to 30 g/cow. CM was quickly absorbed from the udder into the blood circulation; the doses of 12.5 and 25 g/cow were almost completely absorbed within 20 hours. Absorption half‐life (t½>ab) from fully functioning quarters was 57±18 minutes, and the t½>ab from partially functioning quarters was 125±37 minutes. Mean peak serum CM concentrations were 6.1, 16.2, and 37.4 μg/ml after the cows had been infused with 5, 12.5, and 25 g, respectively. These values were considerably higher than the corresponding peak serum CM concentrations reported following intramuscular injection of equivalent doses of the drug. CM residues were not detectible microbiologically in milk from treated quarters 20 hours after treatment with 5 g or 6.25 g, and 36 hours after treatment with 15 g. Drug concentrations in the milk from the non‐treated quarters were approximately 70 per cent of the corresponding serum drug levels. Serum CM concentrations of potential therapeutic value in the treatment of gram‐negative bacterial infections, i.e. > 5 μg/ml, were maintained for 8 hours after cows had been infused with 12.5 g, and for 12 hours after infusion with 25 g. The implications of the improved systemic availability of CM infused by the intramammary route over the intramuscular route are discussed in terms of potential therapeutic efficacy, local irritation, and duration of drug residues.