Comparative pharmacokinetics of doxycycline in cats and dogs.

The disposition of doxycycline hyclate was studied in six adult mixed-breed female cats and six adult mid-sized female dogs following a single intravenous administration of 5 mg/kg body weight. Doxycycline volume of the central compartment, area volume of distribution, volume of distribution at steady state, and total body clearance were significantly smaller in cats. The differences were attributed to more extensive binding of doxycycline to plasma protein including albumin in cats. The significant differences in the volume of distribution and total body clearance were not reflected in elimination half-lives under the conditions of this study (sample size, inhomogeneous population). Doxycycline elimination half-life was 4.56 +/- 0.68 (SEM) h for cats and 6.99 +/- 1.09 h for dogs. Dosage regimens recommended in the veterinary literature were evaluated by the computer program PETDR.