Digoxin: heart rate medicine, blood tests and toxicity signs

Digoxin is a cardiac glycoside. The NHS says it slows your heart rate and makes your heart beat more strongly, which helps blood circulate more effectively. It is used to treat heart rhythm problems, notably atrial fibrillation, and heart failure.

It is used less often than it once was because there are now many alternatives, including ACE inhibitors such as ramipril and lisinopril, valsartan, beta blockers, diuretics and calcium channel blockers. It remains in use for some people.

Most people take digoxin once a day at the same time, often in the morning after breakfast, with or without food. Tablets are swallowed whole with water, and a liquid should be measured with the syringe supplied, not a kitchen spoon. The initial dose may be several tablets taken at once, set by your doctor, and the maintenance dose is usually 125 to 250 micrograms daily.

You will normally take it long term. If you forget a dose, leave it out and take the next at the usual time, and do not double up. If you take more than prescribed, contact NHS 111 immediately; the doctor may order blood tests and an ECG, and you should go to A&E or call 999 if you have severe symptoms.

Most adults can take digoxin. The NHS lists these conditions where checking with a doctor first matters: previous allergy to digoxin, cardiomyopathy, Wolff-Parkinson-White syndrome, heart block, pericarditis, myocarditis, a recent heart attack, kidney impairment, an overactive or underactive thyroid, gut problems or past bowel or stomach surgery, lung disease or severe asthma, rare hereditary galactose intolerance, beriberi, and abnormal levels of potassium, magnesium or calcium.

Because the kidneys clear digoxin, kidney function matters for dosing, and abnormal potassium, magnesium or calcium levels are on the NHS caution list.

Common effects are dizziness, nausea or vomiting, diarrhoea, vision changes such as blurred sight or light sensitivity, and skin rashes. Lie down if dizzy, eat simple meals and drink fluids for nausea or diarrhoea, and do not drive, ride a bike or use machinery while vision is affected.

The NHS warns to contact your doctor if you have more than two of these common side effects, since that may indicate too much digoxin in the blood. Call 999 for a fast heartbeat or palpitations with shortness of breath, dizziness or light-headedness, and for signs of a serious allergic reaction.

Named interacting medicines include amiodarone, verapamil, diltiazem, furosemide and similar water tablets, tetracycline, clarithromycin, erythromycin, rifampicin, trimethoprim, itraconazole, ibuprofen, diclofenac, indomethacin, hydroxychloroquine, chloroquine and several HIV medicines. Check with a pharmacist before buying antacids, kaolin or laxatives, avoid regular anti-inflammatory painkillers unless your doctor agrees, and note that St John's wort can affect digoxin.

Regular blood tests check kidney function and levels of potassium, magnesium and calcium. If a digoxin level is needed, the sample is taken at least 6 hours after your last dose.

Avoid alcohol at first and after any dose change, until you know how it affects you; if you become dizzy, avoid it altogether. During pregnancy digoxin can be taken with specialist supervision, because treating the heart condition matters, and the lowest effective dose is used. It passes into breast milk in very small amounts and is compatible with breastfeeding for a healthy baby. There is no evidence it reduces fertility.

Do not stop suddenly, since it can make the heart condition worse. If side effects trouble you, your doctor may suggest an alternative.