Flomax (tamsulosin hydrochloride) capsule
Detailed View: Safety Labeling Changes Approved By FDA Center for Drug Evaluation and Research (CDER) -- October 2009
- Caution is advised when alpha adrenergic blocking agents including FLOMAX are co-administered with PDE5 inhibitors. Alpha-adrenergic blockers and PDE5 inhibitors are both vasodilators that can lower blood pressure. Concomitant use of these two drug classes can potentially cause symptomatic hypotension.
Drug-Drug Interactions/Cytochrome P450 Inhibition
- Tamsulosin is extensively metabolized, mainly by CYP3A4 and CYP2D6.
- The effects of concomitant administration of a moderate CYP3A4 inhibitor (e.g., erythromycin) on the pharmacokinetics of Flomax have not been evaluated
- A similar increase in exposure is expected in CYP2D6 poor metabolizers (PM) as compared to extensive metabolizers (EM). A fraction of the population (about 7% of Caucasians and 2% of African Americans) are CYP2D6 PMs. Since CYP2D6 PMs cannot be readily identified and the potential for significant increase in tamsulosin exposure exists when FLOMAX 0.4 mg is co-administered with strong CYP3A4 inhibitors in CYP2D6 PMs, Flomax 0.4 mg capsules should not be used in combination with strong inhibitors of CYP3A4 (e.g., ketoconazole).
- The effects of concomitant administration of a moderate CYP2D6 inhibitor (e.g.,terbinafine) on the pharmacokinetics of Flomax have not been evaluated
- The effects of co-administration of both a CYP3A4 and a CYP2D6 inhibitor with Flomax capsules have not been evaluated. However, there is a potential for significant increase in tamsulosin exposure when Flomax 0.4 mg is co-administered with a combination of both CYP3A4 and CYP2D6 inhibitors