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).