ZURICH (Reuters) – The European Union’s drug regulator warned on Wednesday that two older malaria drugs being tested against coronavirus disease (COVID-19) should only be used in trials or national emergency use programmes, citing side effects and uncertain efficacy.

Separately, the U.S. Food and Drug Administration flagged shortages of hydroxychloroquine and chloroquine due to a significant surge in demand.

U.S. President Donald Trump has touted the medicines, approved for malaria, lupus and rheumatoid arthritis, for use against COVID-19. The U.S. Department of Health and Human Services last weekend accepted millions of doses donated by Novartis.

Still, the European Medicines Agency (EMA) urged patients, doctors and other medical professionals, to stick to the medicines’ authorized uses or their use in clinical trials and country-by-country emergency programmes against COVID-19.

The agency cited serious side effects — such as nausea or vomiting — in particular at high doses or when mixed with other medicines.

“Large clinical trials are under way to generate the robust data needed,” the EU’s medicines agency said. “EMA welcomes these trials, which will enable authorities to give reliable advice based on solid evidence to healthcare professionals and patients.”

Trump has predicted hydroxychloroquine could be among “the biggest game changers” in medicine, though Anthony Fauci, the U.S. National Institute of Allergy and Infectious Diseases director, has cautioned that only anecdotal evidence of its effectiveness, including from France, in helping fight coronavirus was so far available.

The FDA, which on Saturday issued an emergency use authorization for the medicines against COVID-19, said there was surging demand.

“Use of the donated medications is expected to help ease supply pressures for the drugs,” the U.S. drug regulator said. “This is a fluctuating and dynamic situation and the FDA is actively engaged.”

The EMA on Wednesday also raised concerns about runs on the medicine, creating supply problems for people taking the drug for approved uses like lupus or arthritis.

In addition to Novartis’s 130-million-dose donation, other companies including Bayer, Mylan, Sun Pharma and Teva have all made supply pledges for the malaria medicines.

COVID-19 studies underway include one with 1,500 people at the University of Minnesota.

(Reporting by John Miller; Editing by Ludwig Burger)