Plasma timolol levels after oral and intravenous administration

The plasma kinetics of timolol administered orally and intravenously to 5 male subjects were examined. Bioavailability was reduced by 25% when the drug was taken orally. Mean plasma half-life after oral dosing was 4.86 h, and after intravenous administration it was 4.56 h; the difference was not significant. The volume of distribution was 3.5 1/k. It is suggested that timolol is little affected by the 'first pass effect', even though there is marked interindividual variation in availability and peak plasma level.