A cheap long-used steroid has been hailed as life-saving breakthrough for critically ill Covid-19 patients but Hong Kong will not use it as a first line treatment after SARS patients who had the drug experienced adverse effects.

A clinical trial by the University of Oxford in Britain said the cheap and commonly available dexamethasone steroid costing less than US$1 (HK$7.80) a day could be effective in saving severe Covid-19 patients connected to ventilators and reduce the death rate by a third.

The British government has been stockpiling dexamethasone while the World Health Organization hailed the trial results as great news. The WHO is set to disclose preliminary results of global trials using several treatments early today.

A British Covid-19 patient, Peter Herring, who tried the dexamethasone treatment said steroids "saved his life." However, many SARS patients who had received high-dosage steroids suffered from adverse side-effects including avascular necrosis - death of bone tissues - due to a lack of blood supply.

Many experienced unbearable pain in their bones and muscles and were unable to walk normally.

During the SARS in Hong Kong in 2003, methylprednisolone - five times less potent than dexamethasone - was widely used to suppress patients' immunity. The coronavirus can trigger excessive immunity response and cause damage to patients' lungs.

In Chinese University of Hong Kong research on SARS in 2013, respiratory expert David Hui Shu-cheong said steroids should only be used when a patient's viral load has gone down but the infection continues to cause overwhelming immunity response.

It was also found that steroids should not be used in the early stage of infection.

The president of the Society of Hospital Pharmacists of Hong Kong, William Chui Chun-ming, said the Hospital Authority learned the lesson from SARS patients and switched its standard steroids from methylprednisolone to the 27-times less-potent hydrocortisone.

"Since then they have been very cautious and conservative about the use of steroids," he said. "I don't think they will ever use dexamethasone on Hong Kong patients.

SARS doubts over Covid-19 drug