Amiodarone × Tamsulosin

Tamsulosin is broken down in the liver mainly by the CYP3A4 and CYP2D6 enzymes (tamsulosin labels). Amiodarone and its metabolite desethylamiodarone inhibit both enzymes and can raise the levels of their substrates (amiodarone SmPC); the US Food and Drug Administration (FDA) classifies amiodarone as a weak inhibitor of CYP3A4 and CYP2D6 (FDA table of CYP inhibitors). There are no data on how much tamsulosin levels rise with this combination. Tamsulosin itself can lower blood pressure, rarely to the point of fainting (tamsulosin SmPC), and higher levels may enhance this effect.

Dizziness and weakness on standing, rarely fainting (tamsulosin SmPC). In older patients, these episodes increase the risk of falls.

Use tamsulosin with caution together with cytochrome P450 inhibitors, which include amiodarone (tamsulosin label of the US Food and Drug Administration, FDA). The FDA label stresses caution especially at doses above 0.4 mg a day; in Spain tamsulosin is taken as 0.4 mg once daily (tamsulosin SmPC). Warn the patient to sit or lie down at the first signs of orthostatic hypotension, such as dizziness or weakness, until they pass (tamsulosin SmPC).