Experts warn that despite the first antiviral pills for COVID-19 promising protection for those at risk of severe disease, Pfizer's or Merck's new medications may not be safe for everyone, NBC News reported over the weekend.

One of the two drugs in Pfizer's Paxlovid antiviral cocktail could cause severe or life-threatening interactions with commonly used medications, including statins, blood thinners and some antidepressants, and the FDA does not recommend Paxlovid for those with severe kidney or liver disease.

In addition, due to concerns about the potential side effects of Merck's molnupiravir, the FDA has restricted its use to adults and only in cases in which other treatments are inaccessible or are not ''clinically appropriate.''

The main concern is that when Paxlovid is paired with other medications that are also metabolized by the CYP3A enzyme, the ritonavir component may boost the co-administered drugs to toxic levels.

The drugs that pose interaction risks are widely prescribed to those at the greatest risk from COVID because of other health conditions, with Peter Anderson, a professor of pharmaceutical sciences at the University of Colorado Anschutz Medical Campus.

He told NBC News that ''some of these potential interactions are not trivial, and some pairings have to be avoided altogether,'' adding that ''some are probably easily managed, but some we're going to have to be very careful about.''

The FDA has published in its Paxlovid fact sheet a list of medications that may interact harmfully with ritonavir, including those that should not be paired with the COVID antivirals.

Pharmacists emphasize, however, that many of the drug interactions are manageable and should not preclude most people from taking Paxlovid.

Emily Zadvorny, a clinical pharmacist who is the executive director of the Colorado Pharmacists Society, told NBC News that pharmacists ''are an excellent source of information and advice about interactions between medications and also supplements and herbal products,'' adding that ''they will help determine if a significant interaction exists and devise solutions to mitigate the interaction if possible.''

Experts are also hopeful that since the Paxlovid treatment is brief, 30 pills, taken as three pills twice a day for five days, the risk of adverse interactions with other medications is low.

''Five days of interactions is not a big deal for the majority of drugs,'' said Jason Gallagher, a clinical pharmacy specialist in infectious diseases at Temple University Hospital in Philadelphia.

Anderson stressed that, despite concerns, ''Paxlovid is a breakthrough drug [that] could make a real difference in the pandemic by making an effective COVID treatment available to many people.''

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