Combined pharmacokinetic and pharmacodynamic studies on alprenolol and 4-hydroxy-alprenolol in man

The effects of orally (100 mg) and intravenously (10 mg) administered alprenolol on the heart rate of 4 exercising healthy volunteers were correlated with the plasma concentrations of alprenolol and its metabolite 4-OH-alprenolol. The metabolite was recovered in plasma after both routes of alprenolol administration and was eliminated from the body at the same rate as alprenolol ( t 1 2 ≅ 3 h ). Infusion of 4-OH-alprenolol (10 mg) significantly reduced the heart rate during exercise. The results indicate that orally administered alprenolol forms the active metabolite 4-OH-alprenolol in sufficiently large amounts to significantly influence the effect of the parent drug. The “first pass” elimination of the oral alprenolol dose was about 90 per cent.