[How to act when an alpha-blocker is associated with a potent inhibitor of CYP3A4]

Combination of alpha-blockers with potent CYP3A4 inhibitors is either contra-indicated or not recommended. We searched data supporting this classification and guiding prescribers when such an interaction occurs.

We analyzed reports published by the French agency for drug safety, reference books and performed search in databases of pharmacokinetics studies and case or case series related with these interactions.

The classification of the potential severity of these interactions defined by the French agency for drug safety evolved over time. Our literature search did not identify any cases or case series reporting serious clinical consequences of such interactions and no pharmacoepidemiological studies on the association between alpha-blockers and inhibitors of CYP3A4. The content of the summaries of product characteristics indicate that the combination of ketoconazole with alfuzosin, silodosin and tamsulosin increases the area under the curve of the alpha-blocker 3 fold.

Data demonstrating the clinical consequences of an association between alpha-blocker and a potent CYP3A4 inhibitor are lacking. The 3 fold increase of the area under the curve for alfuzosin, silodosin and tamsulosin associated with ketoconazole while the association with the two first is contra-indicated and is not recommended with the third raises questions. This lack of data leaves doctors and pharmacists in a situation of uncertainty on how to proceed when such an interaction occurs.