Amiodarone × Dexamethasone

The point of contact is potassium, not cytochrome. The amiodarone label asks for caution with drugs that can cause hypokalaemia or hypomagnesaemia and names diuretics alone or in combination, systemic corticosteroids, tetracosactide and intravenous amphotericin B. In the same document: hypokalaemia alters the effects of amiodarone, increases QT prolongation and the risk of torsade de pointes. Dexamethasone is a potent systemic corticosteroid and produces that potassium loss. Its role as a weak CYP3A4 inducer is real but clinically counts for less than the electrolyte imbalance.

Palpitations, dizziness, presyncope and syncope. On ECG, a prolonged QTc and ventricular ectopy; torsade de pointes can degenerate into ventricular fibrillation. Muscle weakness, cramps and fatigue from low potassium usually come before the arrhythmia.

Potassium and magnesium before dexamethasone starts in someone on amiodarone and during the course, correcting them first if already low. ECG with QTc at the start and at any rhythm symptom. The corticosteroid course is kept to the minimum indicated. If a potassium-wasting diuretic joins the pair, monitoring tightens, because the losses accumulate.