Penbutolol and propranolol: a comparison of their effects on antipyrine clearance in man.

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Abstract
The effects of two beta‐adrenoceptor antagonists, penbutolol (administered on separate occasions as (+/‐)‐ and (‐)‐forms) and propranolol, on the kinetics of antipyrine were studied in eight normal subjects. At the same degree of beta‐adrenoceptor blockade, as assessed by the lowering of exercise tachycardia, propranolol decreased antipyrine clearance by 31 +/‐ 11 s.d.% (P less than 0.001) whereas neither of the two penbutolol formulations had a significant effect. The volume of distribution of antipyrine was unchanged following any of the beta‐adrenoceptor antagonist treatments. The lack of effect of penbutolol on oxidative drug metabolism is not consistent with in vitro data suggesting a relationship between the lipid solubility of beta‐ adrenoceptor antagonists and inhibition of metabolism.