The scramble to develop treatments for Covid-19 has paid off, as some are improving the chances of survival for very sick patients. Since the disease first emerged, medical professionals have gone from fumbling in the dark to a better understanding of what drugs work -- notably steroids and the antiviral medicine remdesivir. Other treatments have shown promise in clinical trials, including an experimental antibody therapy that U.S. President Donald Trump received after testing positive for the coronavirus.

1. What’s the experimental treatment?

Before he left the White House for the hospital on Oct. 2, Trump received a dose of an experimental antibody cocktail made by Regeneron Pharmaceuticals Inc. Early studies indicate the treatment may help patients by reducing coronavirus levels. Usually, patients don’t have access to experimental treatments unless they are part of a clinical trial. Companies sometimes consider special requests for compassionate use in limited circumstances.

Read more: Trump Treatment Thrusts Regeneron Virus Drug to Center Stage

2. What other medicines are used?

• Gilead Sciences Inc.’s antiviral remdesivir was the first medication backed by early clinical data. The U.S. Food and Drug Administration approved the drug Oct. 22, making it the first to obtain formal clearance for treating the coronavirus. Earlier, the FDA had cleared it for emergency use after research showed it helps hospitalized patients recover from Covid-19 more quickly than standard care alone. Subsequent studies from the World Health Organization reported a lack of impact on patient deaths. However, some infectious disease specialists say such antivirals are most likely to be effective when used early, before the infection overwhelms the body.

• In June, a University of Oxford study showed the cheap anti-inflammatory steroid dexamethasone improved survival in patients with Covid-19 who needed breathing assistance, making it the first treatment to show life-saving promise. A generic made by companies including Mylan NV and Merck & Co., dexamethasone fights excessive inflammation, sometimes called a cytokine storm, which can be worse than the viral infection itself.

• Because Covid-19 can cause blood clots that destroy people’s organs, some doctors are finding it helpful to treat patients with blood thinners.

• U.S. regulators in late August controversially granted emergency authorization for infusions of convalescent plasma, an antibody-rich component of blood donated by people who’ve recovered from Covid-19. The authorization is limited to use in hospitalized patients.

3. What’s the controversy over convalescent plasma?

Studies examining the benefits and risks of the therapy haven’t been completed, and experts convened by the U.S. National Institutes of Health broke with the FDA in September, saying there wasn’t enough evidence to recommend for or against the treatment. Critics of the FDA authorization pointed to the agency’s earlier reversal on two malaria drugs.

4. What happened with those?

The FDA in March authorized chloroquine and hydroxychloroquine for use against Covid-19 after Trump repeatedly touted them; he said he’s taken hydroxychloroquine. The FDA’s decision was criticized by other scientists as premature, and in mid-June, the agency reversed itself after determining the drugs were unlikely to work against the coronavirus and could have dangerous side effects. Panic-buying of hydroxychloroquine created shortages of the drug for patients with malaria and the autoimmune disease lupus, for whom it’s a proven therapy.

5. What else is being investigated?

More than 300 projects have been launched to develop and test treatments.

• Antivirals. This would be the drug type of choice but they are a relatively new class of medicine compared with antibiotics and can be challenging to design. Apart from remdesivir, other antiviral drugs that have been tried include favipiravir, a treatment for the flu virus made by Fujifilm Holdings Corp., known for its photo film and cameras but also operating as a health-care company. It sped the recovery of Covid-19 patients with non-severe pneumonia in a late-stage trial in Japan.

• Interferon. New studies published in September focused on the role of an immune substance called interferon that helps orchestrate the body’s defenses. That was an enticing discovery because interferon treatments could help in the early stages of the infection and perhaps prevent life-threatening illness. Interferon deficiencies may underlie about 14% of severe Covid-19 cases, scientists reported.

• Antibody therapies. This is the category Regeneron’s treatment falls under. Making treatment with antibodies widely available requires producing them in a lab rather than continually harvesting fresh batches convalescent plasma. Researchers have considerable hope for this approach, in part because it turned out to be the most effective way to treat Ebola virus, which is fatal about half the time. Another antibody therapy from Eli Lilly and Co. has also yielded promising early results, but a U.S. government-sponsored trial was paused in October out of safety concerns.

6. How do scientists prove a treatment is effective?

Even if a treatment shows promise in laboratory, animal or early human experiments, rigorous testing is needed to prove that it’s both safe and effective. That requires carefully structured and monitored tests known as clinical trials. Typically, these studies are designed to show that patients randomly assigned to get the drug do better than those in a control group who don’t, and that the results aren’t a product of chance. The trials try to subtract all the other influences and factors that might disguise the true effectiveness of the drug. For one thing, patients often recover from viral illness on their own, or improve because of supportive care such as rest and hydration. And some really sick patients might not respond to treatment no matter how effective it is.

7. How long does it take to prove efficacy?

It depends. Drugs that are already approved against one infection and shown to be safe can be tested for effectiveness against another in a matter of months. Experimental drugs may take longer to test, as they have to go through initial studies to evaluate whether they are safe. Other factors that can slow the process include the supply of drug candidates and the availability of patients to test them in. The trials also have to be approved by ethics watchdogs and drug regulators. According to a 2017 review, the median time for regulators to approve a new drug in 2015 was 333 days in the U.S., 422 days in Europe, and 639 days in China. China has since expedited its process. When drugs are deemed to fill an immediate need, regulators can speed them through the approval process using a number of paths, including emergency authorizations.

(Updates with FDA approval of remdesivir.)

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