Moderate
Amiodarone × Tamsulosin
Class III antiarrhythmics (Vaughan Williams)×Alpha-adrenergic blockers for prostatic disorders
Mechanism
Amiodarone is a weak CYP3A4 inhibitor. Tamsulosin is a CYP3A4 and CYP2D6 substrate. Tamsulosin AUC rises moderately, amplifying orthostatic hypotension.
Symptoms
Postural dizziness, syncope, fatigue. In older patients: fall and fracture risk. Also possible: intraoperative floppy iris syndrome during cataract surgery.
Management
On starting amiodarone in a tamsulosin patient, check standing/sitting BP at 1 and 2 weeks. In older patients, do not exceed 0.4 mg/day of tamsulosin. Before cataract surgery, warn the ophthalmologist about tamsulosin (discontinuation 1–2 weeks before does not prevent floppy iris syndrome).
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.