A global trial involving UK health workers of an anti-malarial drug to test its efficacy against the coronavirus comes after Donald Trump said he had begun taking hydroxychloroquine.

Scientists have condemned the use of the drug, which President Trump has championed despite it having not been approved for this purpose outside research or hospital settings.

But what do we know about the drug? Here are some answers to key questions:

What is hydroxychloroquine?

Hydroxychloroquine is a prescription drug used for acute malaria and certain types of arthritis.

It can reduce inflammation, pain, and swelling – and is widely used to treat rheumatic diseases.

It is a derivative of chloroquine, which is also used to treat malaria and will also be trialled as part of the trial led by Oxford University.

Has it been approved to treat Covid-19?

The UK Government has said chloroquine and hydroxychloroquine are not licensed to treat Covid-related symptoms or prevent infection.

It said the drugs should not be used outside ongoing clinical trials which have reached no conclusions over the safety and effectiveness of the medicine on coronavirus.

Dr Stephen Griffin, associate professor in the School of Medicine, University of Leeds, said: “Hydroxychloroquine is not licensed for the treatment or prevention of Covid-19 by the FDA (US Food and Drug Administration), or any other agency.

“In fact the weight of evidence from most recent patient trials shows it to be ineffective, with the potential for adverse side effects including those affecting the heart.”

The FDA did issue an emergency use authorisation to allow the drug to be provided to certain hospital patients, but has since warned against the drug’s use outside clinical trials or hospital settings due to the risk of heart rhythm problems.

How has Mr Trump’s endorsement been received?

Dr Griffin said the president’s remarks were “a staggering, irresponsible act that could very well also amount to self-harm”.

He said hydroxychloroquine was prescribed and monitored carefully due to potential side effects, and as such people following Mr Trump’s example could “endanger themselves”.

Meanwhile, former Government chief scientific adviser Sir David King, said of Mr Trump: “Every word he says should be ignored in terms of advice.

“I’m sorry but this is not the pronouncements of a person who is listening to the scientists. He is making it up as he goes along.”

But why is hydroxychloroquine being considered as a Covid-19 treatment?

According to the authors of a recent French study, attention turned to the drug after a laboratory study reported its potential.

One small uncontrolled study in France on the use of hydroxychloroquine in combination with another drug, azithromycin, found some reduction in patients’ viral load, while another small study found no such benefits.

Chinese researchers recently wrote that hydroxychloroquine is one of a number of drugs being investigated as a Covid-19 treatment based on promising lab results and therapeutic experiences with other coronavirus diseases.

But they emphasised this has not been translated through trials into clinical benefits for patients with Covid-19.

What has recent research found?

Evidence from two recent studies does not support the use of hydroxychloroquine to treat patients with Covid-19.

A study from France involving 181 patients found it did not help to significantly reduce admission to intensive care or death in patients in hospital with pneumonia due to Covid-19.

A randomised clinical trial carried out in China with 150 patients concluded that patients in hospital with mild to moderate persistent Covid-19 who received hydroxychloroquine did not clear the virus more quickly than those receiving standard care.

What risks are there around hydroxychloroquine?

Dr Ayfer Ali, assistant professor of strategy at Warwick Business School and an expert in drug re-purposing said that without a vaccine, using existing drugs could be the “only hope” of treating Covid-19.

But he warned this was not without challenges.

Dr Ali said: “A drug may be less safe for a different disease or in sicker patients.

“For example, preliminary data from the US indicates that patients with Covid-19 who took hydroxychloroquine were more likely to die than patients who did not take the drug.”

What other research is being done?

In mid-April, the Centre for Evidence-Based Medicine (CEBM) said it was aware of 142 trials registered in various national and international databases involving chloroquine and hydroxychloroquine, alone, or in combination.

One example includes the use of a combination of hydroxychloroquine, zinc and azithromycin in a trial aiming to involve patients at Chelsea and Westminster Hospital and West Middlesex University Hospital in London.

The randomised controlled trial will see some patients receive the combination, others will receive favipiravir, a Japanese-made anti-viral drug, while a third group will be given standard care for Covid-19.

The University of Minnesota in the US has launched a clinical trial on whether hydroxychloroquine can prevent people catching coronavirus.

The World Health Organisation (WHO) has also included chloroquine and hydroxychloroquine among drugs being prioritised under its global Solidarity Trial – an international study bringing together various nations’ efforts to test potential coronavirus treatments.

What other concerns are there?

Italian doctors have highlighted that ethics and the availability of drugs needs to be considered as part of any attempt of the widespread use of anti-malarials in the fight against coronavirus.

Concerns have been raised over whether there would be enough supply of chloroquine and hydroxychloroquine should they be used to treat coronavirus.

The European League Against Rheumatism (EULAR) has also said consideration must be given to the potential implications for people who already use the drugs for rheumatic diseases.