Digoxin × Hydrochlorothiazide

Thiazide diuretic causes hypokalaemia and hypomagnesaemia, increasing myocardial sensitivity to digoxin. Arrhythmia risk rises, especially ventricular arrhythmias.

Nausea, vomiting, loss of appetite, confusion, yellow-green halos around lights, arrhythmia (bigeminy, AV block). Symptoms appear earlier in older patients and chronic kidney disease.

On the combination, check potassium and magnesium every 2–4 weeks in the first 3 months, then every 3–6 months. If potassium falls below 4 mmol/L, add potassium supplements or a low-dose potassium-sparing diuretic (spironolactone). Thiazide alternatives in hypokalaemia: indapamide with potassium supplementation or a thiazide/potassium-sparing combination.