A medicine that is prescribed to hundreds of thousands of people who suffer with cramp and restless legs could put them at risk of potentially fatal heart problems, doctors have warned.
Quinine, best known for being added to drinks such as tonic water and bitter lemon, was originally used as an anti-malarial drug before being replaced by modern alternatives.
It is not recommended by either of the UK’s healthcare watchdogs, the National Institute for Health and Care Excellence (NICE) or the Medicines & Healthcare products Regulatory Agency (MHRA). However, a new study has revealed that an astonishing 3.5 million prescriptions are issued for it in the UK every year – and many people take the drug for years.
Quinine, best known for being added to drinks such as tonic water and bitter lemon, was originally used as an anti-malarial drug before being replaced by modern alternatives
It is often given for muscle discomfort, which alongside cramps includes restless leg syndrome – a common condition of the nervous system that causes an irresistible urge to move the legs, or an unpleasant crawling or creeping sensation in the feet, calves and thighs.
The drug is not officially approved for either condition, and researchers suggest that GPs are prescribing it on an ‘off label’ basis. This is a system that allows doctors to use discretion to prescribe a medication if there is evidence that it will help a specific condition as long as patients are aware of the risks.
But researchers from the Royal Free Medical School and University College London found that people taking quinine for more than a year were 25 per cent more than likely to die early than those not taking the drug.
They believe it may have an effect by itself or interact with other drugs patients are taking, such as the heart-failure drug digoxin and certain statins, all officially listed as causing interactions with quinine.
Study author Irwin Nazareth, a Professor of Primary Care at University College London, said: ‘Many patients are on multiple medications and adding in quinine could present problems.’
The drug is known to cause abnormal heart rhythm in some patients, which can trigger heart attacks. It is also known to affect clotting and may cause a heart attack or stroke by causing an artery to become blocked.
Researchers from the Royal Free Medical School and University College London found that people taking quinine for more than a year were 25 per cent more than likely to die early than those not taking the drug
Even small amounts of quinine in tonic water could tip the balance over time. Prof Irwin said: ‘A couple of daily G&Ts wouldn’t ordinarily matter because the amount in soft drinks is small, but if you are already taking quinine medicinally then it could increase your risk.’
The new study, published in the Journal Of The American Medical Association, adds to mounting evidence of the dangers of quinine. The American Food and Drug Administration previously blamed the drug for 665 adverse events and 93 deaths.
In the study, researchers analysed prescriptions issued for quinine at doses of 100mg per day or more for at least a year.
Of 175,000 patients included in their 24-year analysis, about a quarter had been prescribed quinine for muscular cramps or restless leg syndrome.
Prof Nazareth said: ‘My advice to anyone on quinine for these conditions is to stop taking it, and GPs would be well advised not to prescribe quinine.’
Dr Nick Silver, a neurologist at the Walton Centre in Liverpool, said: ‘GPs will prescribe quinine for restless leg because they might confuse it with cramp, where there might be some benefit in its use. But not for restless leg. I would never advocate the use of quinine, as there isn’t the evidence base for its use.’