Pharmacokinetics of oral timolol studied by mass fragmentography

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Abstract
The pharmacokinetics of timolol, after oral administration of single 20 mg doses to healthy subjects, has been studied using an original electron beam ionization GLC-mass spectrometry technique with computer — controlled multiple ion detection. This method of mass fragmentography, tested with propranolol as an internal standard, permitted the measurement of timolol concentrations as low as 1 ng/ml with good precision and accuracy. It enabled the plasma level to be followed up to the twelfth hour after treatment. Individual variation was observed in bioavailability; the peaks plasma concentration (Cmax) of 50 to 103 ng/ml being achieved at different times(0.5–3 h). The residual level after 12 h differed greatly between the subjects (0.8 to 7.2 ng/ml). The mean half-life of the terminal elimination phase was 2.62 ± 0.17 h. Extra-renal elimination (metabolic and biliary) represented the main route of elimination, with a renal to body clearance ratio of 0.123. This level paralleled the percentage of unaltered timolol excreted in urine 24 h after its administration.