By Benjamin Ryan -
NBC News
As rising omicron infections hit a nation weary of the pandemic, the first antiviral pills for COVID-19 promise to offer the protection desperately needed by people at risk of serious complications.
However, experts caution that many people who were prescribed the new Pfizer or Merck drugs will require careful monitoring by doctors and pharmacists, and those antivirals may not be safe for everyone.
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The Food and Drug Administration has authorized the use of Pfizer's drug Paxlovid for mild to moderate COVID cases in people as young as 12 years old and suffering from underlying conditions such as heart disease or escalating diabetes. the risks of hospitalization and death from coronavirus.
However, one of the two substances in the antiviral cocktail could cause serious or life-threatening interactions with widely used medications such as statins, blood thinners, and some antidepressants.
And the FDA does not recommend the use of Paxlovid in people with severe kidney or liver disease.
Due to expert concerns about the potential side effects of Merck's molnupiravir, the FDA has restricted its use to adults and only in settings where other licensed treatments, including monoclonal antibodies, are inaccessible or not "clinically appropriate. ".
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Paxlovid consists of two tablets of the antiviral nirmatrelvir and one tablet of ritonavir, a drug that has long been used as a stimulating agent in HIV treatments.
Ritonavir suppresses a key liver enzyme called CYP3A, which metabolizes many drugs, including nirmatrelvir.
For Paxlovid treatment, ritonavir slows down the breakdown of the active antiviral in the body and helps it stay at a therapeutic level for a longer time.
This stimulating effect was likely to have been crucial in driving Paxlovid's high efficacy in clinical trials.
When Paxlovid is combined with other drugs that are also metabolized by the CYP3A enzyme, the main concern is that ritonavir may increase the co-administered drugs to toxic levels.
To complicate matters, drugs that pose interaction risks are widely prescribed for people at increased risk for COVID due to other health conditions.
Among those drugs are anticoagulants, anticonvulsant drugs;
medications for irregular heart rhythms, high blood pressure, and high cholesterol;
antidepressants and anxiolytics;
immunosuppressants;
steroids (including inhalers);
HIV treatments;
and erectile dysfunction medications.
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"Some of these potential interactions are not trivial, and some combinations should be avoided entirely," said Peter Anderson, professor of pharmaceutical sciences at the University of Colorado Anschutz Medical Campus.
"Some can probably be handled easily. But, in other cases, we will have to be very careful."
In its fact sheet on Paxlovid, the FDA has published a detailed list of drugs that can harmfully interact with ritonavir, including those that should not be combined with COVID antivirals.
However, experts emphasize that many drug interactions are manageable and should not prevent most people from taking Paxlovid.
"Pharmacists are highly trained experts in drug safety and monitoring and are an excellent source of information and advice on interactions between drugs and herbal supplements and products," said Emily Zadvorny, clinical pharmacist and executive director of the Society of Pharmacists of Colorado.
"They will help determine if there is a significant interaction and come up with solutions to mitigate the interaction, if possible."
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"A revolutionary medicine"
The good news is that healthcare providers have experience using ritonavir among people with HIV, a group that often takes medications for other health conditions in addition to antiretroviral therapy.
William Werbel, an assistant professor of medicine at Johns Hopkins University who specializes in infectious transplant diseases, advised people at high risk for complications from COVID-19 to speak with their healthcare providers, as well as a knowledgeable pharmacist. , about changes they could make to their treatments if they need Paxlovid, even before they become infected with the virus.
Anyone using Paxlovid, which must be prescribed within five days of the first symptoms, should make sure to inform their prescribers and pharmacists of the full list of other over-the-counter medications and supplements they are taking, Anderson said.
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Some medications, such as statins, are more likely to be stopped during treatment with COVID pills, Anderson said.
For example, it would be preferable to continue taking certain blood thinners but reduce the doses.
Some heart rhythm medicines cannot be taken with Paxlovid.
On the contrary, some anticonvulsant drugs can stimulate the metabolic action of liver enzymes and thus reduce the levels of Paxlovid in the body, as can the herbal supplement St. John's Wort.
The FDA cautioned that these treatments should not be combined with Paxlovid.
Since the treatment with Paxlovid is brief (three pills taken twice a day for five days), experts are hopeful that the risk of adverse drug interactions is low.
"Five days of interactions is not a big problem for most drugs," said Jason Gallagher, an infectious disease clinical pharmacy specialist at Temple University Hospital in Philadelphia.
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If a potential drug interaction with Paxlovid poses too great a risk, Anderson said, a safe and effective alternative therapy against COVID-19 would be GlaxoSmithKline's sotrovimab, the only licensed monoclonal antibody treatment that research has shown to neutralize reliably the omicron variant of the virus.
Otherwise, the antiviral molnupiravir is an option, albeit with much less efficacy than Paxlovid or sotrovimab.
Despite the concerns of using Paxlovid in conjunction with other prescription drugs, experts are excited about the drug's potential.
"Paxlovid is a revolutionary drug," Anderson said.
"This could make a real difference in the pandemic because effective Covid treatment would be available to many people."
