Pharmacokinetics of furosemide after intravenous, oral and transdermal administration to cats.

OBJECTIVES: The aim of this study was to determine the pharmacokinetics of furosemide in cats following intravenous (IV), oral and transdermal administration.

METHODS: This study used six healthy adult cats in a three-phase design to compare plasma furosemide concentrations in cats that received one IV 2 mg/kg dose of furosemide, one oral 2 mg/kg dose of furosemide and 3 days of q12h dosing with 2 mg/kg furosemide transdermally applied to the ear pinna.

RESULTS: After IV administration the elimination half-life was (mean and coefficient of variation) 2.25 h (72%), systemic clearance was 149 ml/kg/h (27.4%) and volume of distribution was 227 ml/kg (22%). After oral administration the terminal half-life was 1.2 h (18.7%), peak concentration was 3.4 μg/ml (51.7%) and bioavailability was 48.4%. The transdermal plasma concentrations were undetectable or very low at most time points, and pharmacokinetics were not determined from the transdermal dose.

CONCLUSIONS AND RELEVANCE: Furosemide was rapidly eliminated in cats after oral and IV administration and is probably best administered orally at least q12h in cats with heart failure. The oral dose absorbed was approximately 50%, but the absorption from transdermal administration was negligible.