7 DRUG INTERACTIONS
7.1 CYP 3A4 Inhibitors
No in vivo drug interaction studies were conducted with CARDURA XL.
In vitro studies suggest that doxazosin is a substrate of CYP 3A4. Caution should be exercised when concomitantly administering CARDURA XL with a strong CYP 3A4 inhibitor, such as atanazavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, or voriconazole [see Clinical Pharmacology (12.3)].
7.2 Antihypertensive Medications
Pharmacodynamic interactions between CARDURA XL and antihypertensive medications or other vasodilating agents have not been determined.
7.3 PDE-5 Inhibitors
Concomitant administration of CARDURA XL with a PDE-5 inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension [see Dosage and Administration (2.3)].