Dexamethasone Concentrations in Bovine Blood Plasma and Milk After Intravenous Injection

Abstract

Passage of dexamethasone from plasma to milk in five lactating dairy cows after an intravenous injection was evaluated by a high performance liquid chromatographic technique for measurement of concentrations in blood plasma and milk. The dexamethasone ester was 21-isonicotinate as a solution and was administered at .1 mg/kg bodyweight. The drug was detected in milk postinjection from 15 min to 8 h with a peak concentration of 20.6 ng/ml at the second sample time (30 min). Half-times of dexamethasone in plasma and milk were 4.5 and 3.0 h. The ratio of mean concentration for milk/plasma was .39. It is anticipated that no residues of dexamethasone would be detected in milk if normal dairy practices are followed.