NEW YORK (BLOOMBERG) - The drug touted by United States President Donald Trump as a possible line of treatment against the coronavirus comes with severe warnings in China and can kill in dosages as small as 2g.

China, where the deadly pathogen first emerged in December, recommended the decades-old malaria drug chloroquine to treat infected patients in guidelines issued in February after seeing encouraging results in clinical trials. But within days, it cautioned doctors and health officials about the drug's lethal side effects and rolled back its usage.

This came after local media reported that a Wuhan Institute of Virology study found that the drug can kill an adult dosed at just twice the daily amount recommended for treatment, which is 1g.

As the drug has not been approved by the US Food And Drug Administration to treat the disease known as Covid-19, the Chinese experience may be useful as the American regulator studies the medication which has been endorsed by Mr Trump as well as Tesla chief executive officer Elon Musk.

The pandemic, which has sickened more than 235,000 globally and killed over 9,800 people, has triggered growing anxiety across the US as states say they lack testing kits and medical equipment. California instituted a statewide lockdown on Thursday (March 19) to slow the outbreak.

Chloroquine was among the first group of therapies Chinese scientists identified as being effective in curbing the new coronavirus. Clinical trials on about 130 patients demonstrated the drug's ability to reduce the severity of the illness and speed up virus clearance, according to China's Ministry of Sciences and Technology.

Chloroquine phosphate was officially recommended on Feb 19 in the Covid-19 treatment guidelines published by China's National Health Commission, along with a few other drugs such as AbbVie Inc's Kaletra and flu drug arbidol as antiviral treatments for patients. The commission recommended no more than a 10-day course of chloroquine for adult patients at 500mg - half a gram - twice a day.

As hundreds of clinical trials are launched to study potential Covid-19 treatments, stocks of drugmakers and biotechnology companies have racked up big gains on the hope that the industry will see a windfall. But the history of previous viral outbreaks like Ebola and Zika show little success in producing viable treatments. Some potential drugs were developed only after the epidemics already waned through containment measures.

Closely watched

China's recommendation to use chloroquine in treatment was quickly followed by a warning.

Two days after the treatment guideline update, the health authorities in Hubei province - China's worst-hit region, where the outbreak started and which accounted for the majority of its over 80,000 patients - asked hospitals to closely watch for, and immediately report, any adverse side effects of chloroquine phosphate, according to a report in local media outlet The Paper.

Related Story Coronavirus: China looking at using stem cell therapy to treat severe cases

The drug is known to have short-term side effects such as nausea, diarrhoea and tinnitus, while long-term use can irreversibly impair eyesight. It is forbidden for pregnant women, as it can cause congenital defects in babies.

The China Health Commission revised the dosage in a Feb 29 notice tightening chloroquine use. The drug cannot be given to pregnant women, those with heart disease, terminal liver and renal disease, retina and hearing loss and patients on antibiotics such as azithromycin and steroid.

It can now be given only to patients between 18 and 65 years of age for a seven-day treatment course. Patients weighing over 50kg can take 500mg twice a day - the usual dose - while those weighing less will be administered the drug just once a day after two days of use, according to the latest guidelines.