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 just dosed at twice the daily amount recommended for treatment, which is one gram.

As the drug hasn’t been approved by the U.S. 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 Trump as well as Tesla Inc. 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 U.S. as states say they lack testing kits and medical equipment. California instituted a state-wide lockdown on Thursday 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.

Chroloquine 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, health authorities in Hubei province — China’s worst-hit region where the outbreak started and which accounted for 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.

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

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 to 65 years of age for a seven-day treatment course. Patients weighing over 50 kilograms (110 pounds) 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.

A woman in Wuhan proved how lethal chloroquine can be when it’s taken beyond the recommended dose. On Feb. 25, Shanghai-based The Paper reported that she took 1.8 grams of the drug she ordered online after suspecting she had the coronavirus. She did not, but the drug caused her to develop malignant cardiac arrhythmic, which can cause sudden death, and she was admitted to the intensive care unit.

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