Drug Interaction Report

MONITOR: Nonsteroidal anti-inflammatory drugs (NSAIDs) may decrease the antihypertensive effect of prazosin. The proposed mechanism is NSAID-induced inhibition of prostaglandin synthesis. Data are available for indomethacin. A similar interaction is expected with other NSAIDs.

MANAGEMENT: The patient's blood pressure should be monitored during coadministration, and the dosage adjusted as necessary.

GENERALLY AVOID: The concurrent use of ethanol and alpha-1 adrenergic blockers may cause increased hypotensive effects. Patients with aldehyde dehydrogenase deficiencies (primarily Asians) may be at a higher risk of this interaction. The mechanism has not been determined. Data exist for prazosin and other alpha adrenergic blockers are expected to interact also. In addition, any patients taking alpha adrenergic blockers may experience excessive orthostatic hypotension with ethanol ingestion, due to ethanol's unopposed vasodilatory effects in the presence of alpha adrenergic blockade.

MANAGEMENT: Patients who develop a flushing reaction after ethanol ingestion (indicates a possible aldehyde dehydrogenase deficiency) should be advised to avoid ethanol or limit their intake. All patients should be warned about the possibility of orthostatic hypotension with concurrent ethanol use.