Pharmacokinetics of quinidine sulfate in dairy cattle

Pharmacokinetic profile and therapeutic range of plasma quinidine concentration were determined in dairy Holstein cows. Plasma half-life of intravenous quinidine was 1.28 +/- 0.492 (0.41-1.65) hr. The pattern of plasma quinidine transition after oral administration varied greatly among individuals. Total body clearance was 58.7 +/- 24.49 ml/min/kg, although renal quinidine clearance was 0.76 +/- 0.441 ml/min/kg. Therefore, the involvement of some extrarenal organ as the main site of excretion was suspected. Seven cows, diagnosed as atrial fibrillation or ventricular premature contraction, were orally administered with quinidine at various dosages. They showed plasma concentration of 2.3 +/- 1.59 mg/l when therapeutic effect was observed. Clinical signs of intoxication were observed at plasma quinidine concentrations over 10 mg/l. These results suggest the difficulty with the maintenance of effective plasma quinidine concentration by an oral or a single intravenous administration, and thus it is concluded that use of quinidine for treatment arrhythmic cows must be carefully done in order to avoid possible intoxication.