Blood pressure may fall sharply when calcium-channel blockers are first given to patients already taking alpha blockers (particularly alfuzosin, prazosin, bunazosin and terazosin), and vice versa. In a small study, tamsulosin did not have any clinically relevant effects on blood pressure well controlled by nifedipine. Verapamil may increase the AUC of prazosin and terazosin. Alpha blockers and calcium-channel blockers may be combined for additional blood pressure lowering in patients with hypertension.
It is recommended that patients already taking calcium-channel blockers should have the dose reduced and start with a low-dose of alpha blocker, with the first dose taken just before going to bed. Caution should also be exercised when calcium-channel blockers are added to established alpha blocker therapy. Patients should also be warned about the possibility of postural hypotension and how to manage it (i.e. lay down, raise the legs, and get up slowly when recovered).
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