Oral drugs most commonly used are calcium channel blockers: Sustained-release diltiazem 120 to 540 mg once a day Sustained-release verapamil 120 to 480 mg once a day (dose must be reduced in patients with renal or hepatic dysfunction) Amlodipine 5 to 10 mg once a day (dose must be reduced in older patients and in patients with hepatic dysfunction) Although all these drugs relieve symptoms, they do not appear to alter prognosis.