Ketoconazole increases alfuzosin
levels 2.3-fold. Protease inhibitors
are predicted to interact similarly (CYP3A4 inhibition).
The manufacturers cautiously contraindicate potent CYP3A4 inhibitors (they name ritonavir). If concurrent use is essential it would seem prudent to use the minimum dose of the alpha blocker and titrate as necessary, monitoring for adverse effects, particularly first-dose hypotension. The risks are likely to be greater in patients also taking other antihypertensives
. Other alpha blockers
do not interact, and may therefore be suitable alternatives.