The pharmacokinetics of acebutolol have been studied in eight healthy male volunteers following the oral administration of acebutolol hydrochloride ('Sectral', May & Baker) as a single dose (400 mg), and during and after repeated oral dosing (400 mg, b.d. for 56 days). Following single dose administration, considerable inter-subject variation in plasma levels of parent drug and the major metabolite, diacetolol, was evident. Acebutolol appeared to be eliminated from plasma in a bi-phasic manner, and this was confirmed from urinary excretion rate data. Mean initial and terminal half-lives of about 2 and 11 h, respectively, were determined. Plasma levels of diacetolol were greater than those of parent drug from 3 to 4 h following dose administration. Total urinary excretion of diacetolol was generally greater than that of acebutolol. During repeated dosing, steady-state plasma levels of acebutolol and diacetolol were achieved in 6 volunteers. Acebutolol did not appear to stimulate or inhibit its metabolism.
A new stereospecific hplc method that is capable of simultaneously quantitating the S-(-)- and R-(+)-enantiomers of acebutolol and its major metabolite, diacetolol, in plasma and urine, is described. When applied to the assay of biological fluids collected during single and chronic oral dosing with acebutolol (Sectral), this procedure failed to reveal any important stereoselectivity in the disposition of either acebutolol or diacetolol in man. This may occur because acebutolol is metabolized by hydrolysis and N-acetylation, whereas the other beta-blockers which exhibit some degree of stereoselective disposition (e.g. metoprolol and propranolol) are primarily metabolized by oxidation.
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