Penbutolol: a new beta-adrenergic blocking agent

Penbutolol is a new beta-adrenergic blocking drug approved for the treatment of hypertension. It is a noncardioselective beta-blocker and has intrinsic sympathomimetic activity. The drug is approximately four times as potent as propranolol when taken orally. After oral administration, it is almost completely absorbed and peak plasma concentrations are achieved within 1.0 to 2.25 hours. Penbutolol is extensively metabolized in the liver by hydroxylation and glucuronidation. Active metabolites have not been identified. Only four to six percent of the parent drug is eliminated in the urine unchanged and dosage adjustment in renal insufficiency does not appear to be necessary. The mean terminal half-life of penbutolol is 17.6 to 26.5 hours. The duration of the hypotensive effect is approximately 24 hours. Current dosing guidelines recommend initiating therapy with 20 mg/d administered once a day. Optimum hypotensive effect occurs at dosages of 20-40 mg/d with little additional benefit observed above this range. Penbutolol appears to be well tolerated. The adverse effect profile is similar to other beta-blockers.