PHARMACOKINETICS AND BIOAVAILABILITY OF O RALLY-ADMINISTERED TETRACYCLINE IN DOGS AND CATS

The bioavailability of tetracycline was determined in healthy dogs and cats after oral administration of 20 mg/kg tetracycline (Tetraseptin( R) mite Suspension, Chassot and Cie AG, Switzerland). The oral dose wa s given thrice a day in 8 hours intervals. To calculate the absolute b ioavailability of orally administered tetracycline, a formulation for intravenous administration (Supramycin(R) pro infusione) was injected intravenously at the same dose. The tetracycline concentration was mea sured in plasma samples by HPLC after solid-phase extraction. In dogs, maximum plasma concentrations of tetracycline between 1.9 to 5.0 mu g /ml were measured within 1.5 to 2 hours after oral administration. The mean half-life of elimination was 4 hours. After intravenous administ ration, the half-life of elimination was between 1.6 and 2 hours. In c ats, maximum plasma concentrations ranged from 3.5 to 11.0 mu g/ml. Th e mean half-life of elimination was 2.7 hours after oral treatment and 2.5 hours after intravenous administration. The data demonstrate a te tracycline bioavailability of about 40 per cent in dogs and 50 percent in cats after oral administration of Tetraseptin(R) mite Suspension. A large variability of bioavailability is obvious. For oral tetracycli ne treatment on the empty stomach, a dosage of 20 mg/kg body weight gi ven thrice a day with a dosage interval of eight hours is recommended.