US May Add ‘Toxic’ Antiviral Drug to Arsenal as Monkeypox Spreads

In order to contain the monkeypox outbreak that has resulted in more than 1,400 US cases, US health officials may open access to an antiviral drug that has been little-studied in humans.

The US Centers for Disease Control and Prevention is working on an expanded access protocol for Chimerix Inc. The drug could be used as a back-up in some patients who don't respond to other therapies.

Even as the number of cases grows and experts warn that the disease may prove hard to stamp out in the US, the Biden administration has promoted US readiness for monkeypox because of years of work guarding against an outbreak of smallpox. The White House is concerned about the strains on the vaccine supply.

The US Food and Drug Administration greenlights drugs when they can't be studied in people. In order to assess Tembexa's effectiveness, rabbits and mice were used. Some patients had to stop using the drug due to side effects after contracting viral infections from stem cell transplants.

The medicine has a black box warning on it's label that says it has an increased risk of death when used for longer than two weeks. It can cause a variety of symptoms. 4% of patients stopped using the drug due to its adverse effects according to the FDA.

Luciana Borio was the former director of medical and biodefense readiness at the US National Security Council.

Tembexa is linked to a number of health issues, including gastrointestinal issues, and may lead to infertility. The CDC wants to use it to help patients suffering from serious or life threatening conditions. Chimerix agreed to sell Tembexa to Emergent in May, but that deal has not yet been completed.

Another Option

The mortality rate in the US has not been reported, but many patients are experiencing distress and uneasiness from their symptoms. Mary Foote is an infectious disease specialist from New York City.

According to Foote, up to 25% of patients need treatment for their symptoms. Siga Technologies Inc.'s Tpoxx is one of the drugs that the US has in the Strategic National Stockpile. The drug can be used for monkeypox.

The US hasn't yet used Tembexa to treat monkeypox patients, but if it becomes available in the US, it could be used for severe cases that don't respond to Tpoxx.

There isn't much data on the drug's effectiveness. According to a recent study, Tembexa didn't provide a convincing benefit in three patients. The researchers don't know if giving it to people earlier or at a different dose would lead to different outcomes. Three patients who were treated with the drug had to stop the therapy because of elevated liver enzymes.

The study was limited by the low patient number and omission of notable background and context on the patients evaluated, according to Chimerix. Researchers associated with Chimerix conducted a risk-benefit study and found that Tembexa was well-tolerated in adults and children.

Drug Interactions

The drug brincidofovir can have adverse interactions with other drugs. According to a recent update from the World Health Organization, over 40% of monkeypox patients whose HIV status was known were positive.

The risk of increased mortality is serious and severe if given in other disease states where the safety and effectiveness of brincidofovir has not been established.

Before starting treatment with brincidofovir for monkeypox, risks and benefits need to be discussed with patients and providers, according to an email from the CDC.

Other countries are looking to get supplies of Tembexa as the global outbreak continues. Chimerix said in a statement that it had seen an increase in interest, including two non- US procurement contracts. The company is in talks with the US Biomedical Advanced Research and Development Authority to include Tembexa in the US inventory.

The bulk of the orders for Tpoxx are with Canada. The company said in an email that there were other orders from Europe and Asia Pacific.