Severe first-dose hypotension, and synergistic hypotensive effects that occurred in a patient taking enalapril with bunazosin have been replicated in healthy subjects. The first-dose effect seen with other
alpha blockers (particularly
alfuzosin, prazosin and terazosin) is also likely to be potentiated by
ACE inhibitors. In one small study tamsulosin did not have any clinically relevant effects on blood pressure that was already well controlled by enalapril.
Acute hypotension (dizziness, fainting) sometimes occurs unpredictably with the first dose of some
alpha blockers (particularly
alfuzosin, prazosin and terazosin), and this can be exaggerated by beta blockers and
calcium-channel blockers.
ACE inhibitors would be expected to have a similar effect. Minimise the risk by starting with a low dose of alpha blocker, preferably given at bedtime, and escalate the dose slowly over a couple of weeks. It is recommended that the dose of ACE inhibitor is reduced during initiation. Patients should be warned to lie down if
symptoms such as dizziness,
fatigue or sweating develop, and to remain lying down until
symptoms abate.