The scramble to develop treatments for Covid-19 has paid off. A number of therapies 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, who’s sick with the coronavirus, arranged to take.

1. What’s the experimental treatment?

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

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

2. What other medicines are used?

• In the hospital, Trump was given remdesivir, an antiviral drug and the first medication backed by early clinical data. It was cleared by the U.S. Food and Drug Administration May 1 for emergency use after research showed that the medicine, made by Gilead Sciences Inc., helped hospitalized patients recover from Covid-19 more quickly than standard care alone.

• Trump’s doctors also said he’s been given the low-cost, anti-inflammatory drug dexamethasone. In June, a University of Oxford study showed the commonly used steroid improved survival in patients with Covid-19 who needed breathing assistance. It became the first treatment to show life-saving promise months into the pandemic. Made by drugmakers including Mylan NV and Merck & Co., dexamethasone is useful against one of Covid-19’s most destructive effects: 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 a treatment using blood plasma donated by people who’ve recovered from Covid-19. The authorization is limited to use in hospitalized patients.

3. What’s the controversy over blood plasma?

The treatment involves collecting plasma, the liquid part of blood, from people who’ve recovered from Covid-19 and developed antibodies to the virus, and transfusing it into those who are still sick. Studies examining the benefits and risks of the therapy haven’t been completed. A panel of 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. Skeptics of the FDA’s decision pointed to the agency’s earlier reversal on two malaria drugs.

4. What happened with the malaria drugs?

The FDA in March authorized chloroquine and hydroxychloroquine for use against Covid-19 after Trump repeatedly touted the drugs. The FDA’s decision was criticized by scientists as premature, and in mid-June, the agency revoked the authorization 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 is a proven therapy.

5. What else is being investigated?

More than 300 projects have been launched to develop and test treatments, some of which have opened up strategies for identifying patients that are at high risk of developing the life-threatening form of the illness.

• 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 a substance called interferon that helps orchestrate the body’s defenses. That was an enticing discovery because interferon treatments could be efficacious in the early stages of the infection and help prevent life-threatening illness.

• 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 from individuals. 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. In addition to Regeneron’s approach, another by Eli Lilly and Co. has shown promising early results.

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 Trump’s use of remdesivir and dexamethasone.)

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