Digoxin is a drug used to treat heart failure and irregular heartbeats known as a “cardiac glycoside”. It is obtained from the leaves of the foxglove plant (Digitalis lanata) and is available in Australian as the brands Lanoxin and Sigmaxin.
How it works
Digoxin is used in people with heart failure because of its ability to increase the force of heart muscle (myocardial) contraction, which improves its pumping power. It also decreases oxygen consumption, which helps the heart do more with less oxygen.
Digoxin works by inhibiting the sodium pump within heart muscle cells. This increases sodium in the cells, which in turn increases calcium content, leading to increased force of heart contractions. Digoxin also has effects on electrical activity in the heart and is most widely used in people with abnormal heart rhythm (atrial fibrillation).
It has also been previously used to treat the symptoms of congestive heart failure.
In the modern era, digoxin was considered, for many years, the mainstay of treatment for people with heart failure. However, this has changed over the last decade as it has been replaced as first-line treatment with other medicines which are generally safer to use and known to improve patient survival.
Evidence from clinical trials found treatment with digoxin did not reduce mortality in people with heart failure. The drug is now recommended as second-line treatment for people with severe heart failure who also have heart rhythm problems.
How it was developed
Digoxin was first isolated from the foxglove plant by Dr Sydney Smith at Burroughs Wellcome in Britain in 1930.
However, Dr William Withering is credited with the first trials of foxglove extract to treat a condition called “dropsy” (fluid retention usually associated with heart failure). These were reported in his 1785 paper, An account of the foxglove and some of its medical uses; with practical remarks on dropsy and other diseases.
Even in these trials Withering identified that, while foxglove extract could help his patients, it was associated with severe side effects in some people, which he described as vomiting, purging, giddiness, confused vision and slow pulse.
How it makes you feel
Digoxin is known to have a narrow safety margin – the dose used for effective treatment is close to the dose that can cause adverse effects. At the correct dosage digoxin will reduce a patient’s heart palpitations and improve their symptoms of heart failure (which includes reducing shortness of breath).
If the dosage is too high, patients can experience delirium and depression, and it can adversely affect heart rhythm (arrhythmia), causing palpitations (or worse, death).
Digoxin is one of the few medicines in current use where we have a specific antidote for people who are experiencing digoxin toxicity. Called DigiFab (digoxin-specific antibody fragment), this can reduce the concentrations of the drug in the body.
Digoxin is not suitable for everyone, especially people with complicated types of heart rhythm problems because digoxin can make these problems worse. Careful dosing is particularly needed in older people (especially if they have poor kidney function) and young children with a heart condition. The common digoxin brand name for the lower dose (62.5 micrograms) is Lanoxin PG, where the “PG” refers to Paediatric and Geriatric.
Interactions and side effects
Digoxin interacts with a range of other medicines that people may be taking, including St John’s wort, which reduces the effectiveness of digoxin.
Digoxin (even at therapeutic doses) can cause nausea, vomiting, diarrhoea, visual disturbances (such as blurred vision and xanthopsia (where you see yellow/green halos around objects), drowsiness, dizziness, headache, fatigue and rash.
Cost and use
Digoxin is relatively inexpensive — costing patients around 20 cents a tablet on the Pharmaceutical Benefits Scheme — and less expensive if a person has a concession card.
Digoxin is a relatively common medicine for heart conditions. In the last 12 months, 350,000 prescriptions for digoxin were dispensed on the Pharmaceutical Benefits Scheme in Australia. However, its use is declining since medications with greater proven effectiveness and safety are preferred.
Was Van Gogh taking foxglove extract?
One of the interesting stories in the history of digoxin is the link with Vincent Van Gogh. Much has been written about the physical and mental health problems that Van Gogh had in his life and numerous diagnoses have been proposed.
Among these diagnoses is the suspicion that he suffered from digitalis (foxglove) toxicity, which resulted in the frequent use of yellow halos in his paintings due to xanthopsia. This is very evident in paintings such as Starry Night and The Night Café.
Others argue digitalis toxicity could not have caused Vincent’s yellow palette because sustaining that level of xanthopsia would have surely been lethal and Dr Gachet was unlikely to overdose Van Gogh because he practised homeopathy. But it does make for an interesting story, and an even better painting!