Oxford University said on Wednesday it would study whether the world's best-selling prescription medicine, adalimumab, was an effective treatment for Covid-19 patients - the latest effort to repurpose existing drugs as potential coronavirus therapies.

Adalimumab, which is sold under the brand name Humira by AbbVie, is a type of anti-inflammatory known as an anti-tumour necrosis factor (anti-TNF) drug. Recent studies have shown that Covid-19 patients already taking anti-TNF drugs for inflammatory bowel disease and inflammatory arthritis are less likely to be admitted to hospital, Oxford said in a statement.

Oxford's trial, called AVID-CC, will be aimed at treating people in the community, especially in care homes, the university said. It will enrol up to 750 patients from community care settings throughout Britain.

Humira is used to treat a range of conditions including rheumatoid arthritis, ulcerative colitis and psoriasis.

The availability of biosimilar versions of the medicine would make it affordable and accessible if the trial is successful, Oxford said. Novartis makes one of the alternatives, Hyrimoz

Research has identified some treatments for hospitalised Covid-19 patients, including Gilead's remdesivir as well as the generic steroid drug dexamethasone.

Researchers have also studied other anti-inflammatory drugs for treating Covid-19. Severe infections are believed to be triggered by an over-reaction of the immune system, known as a cytokine storm, and drugs that suppress certain elements of the immune system can play a role in arresting a rapid escalation of symptoms.

But there are as yet no effective therapies for people who are not admitted to hospital.

Care homes were particularly hard hit by the first wave of Covid-19 in the UK and other countries. If Humira were successful against Covid-19, this could help some older people who are some of most vulnerable, it said, at a time when governments are struggling to contain the pandemic.

The Oxford study is funded by the Covid-19 Therapeutics Accelerator initiative set up by global health charity Wellcome, as well as the Bill and Melinda Gates Foundation and Mastercard.