Pharmacokinetics of atenolol in clinically normal cats

To determine the pharmacokinetics of atenolol (AT) after i.v. and oral administrations in cats, to assess duration of beta-blocking effect, and to determine whether AT can be effectively used once per day.

9 clinically normal cats.

Single doses of 1 (i.v.) or 3 (oral) mg of AT/kg of body weight were administered to each cat on different occasions, and serial blood samples were collected. Plasma concentrations of AT were subsequently determined, using high-performance liquid chromatography. The plasma concentration data were analyzed, using noncompartmental analysis. An isoproterenol challenge test was used to determine the beta-blocking effect of AT on heart rate after 3 consecutive days of oral treatment (3 mg/kg, once a day).

After i.v. administration, mean +/- SD apparent volume of distribution at steady state and systemic clearance values were 1,088 +/- 148 ml/kg and 259 +/- 72 ml/h/kg, respectively. Bioavailability was 90 +/- 9% after oral administration. The half-life values were 3.44 +/- 0.5 and 3.66 +/- 0.39 hours after i.v. and oral administrations, respectively. Compared with baseline values prior to AT administration, heart rates at 6 and 12 hours after administration of AT were significantly reduced.

AT has high oral bioavailability in cats, resulting in small interindividual variability in its kinetics in this species. The drug has beta-blocking effect in cats, as indicated by the attenuated heart rate response to isoproterenol; this effect persists for at least 12 hours in clinically normal cats.