Newer antihypertensive agents. Three recent additions to the list of antihypertensive agents have been approved for use as monotherapy or in combination with other drugs. Betaxolol hydrochloride (Kerlone) maintains its effect for 24 hours, making it a true once-a-day beta blocker. Penbutolol sulfate (Levatol) is as effective as other beta blockers and diuretics. Doxazosin mesylate (Cardura), a selective alpha 1 blocker, also allows once-a-day dosing and has produced favorable changes in lipid profiles. Two new drug delivery systems, one for verapamil hydrochloride (Verelan) and one for extended-release nifedipine (Procardia XL), allow less frequent dosing and may offer other advantages, such as greater compliance and a more tolerable side-effect profile. 