Merck has defended the safety profile of its Covid antiviral pill and claimed a rival treatment developed by Pfizer will create problems for some patients taking drugs for other medical conditions.
The criticism of a rival’s product from Merck comes as the US Food and Drug Administration considers whether to authorise its antiviral drug molnupiravir, the first easy-to-administer oral treatment for Covid-19.
Last week a panel of external experts at the FDA voted narrowly in favour of giving the green light to Merck’s drug by a margin of 13 to 10. But some members raised concerns over its effectiveness and safety, including whether it could cause birth defects if taken by pregnant women or potentially help spawn new Covid variants.
In an interview with the Financial Times, Eliav Barr, senior vice-president of global medical affairs at Merck, said both antiviral drugs are needed to protect people from the virus as some patients may not be able to take one or other of the treatments due to possible side-effects.
However, a requirement for Pfizer’s antiviral pill to be taken with ritonavir, a drug used to treat HIV, would make the treatment unsuitable for many people with pre-existing medical conditions, he added.
“Ritonavir, which has been used in HIV therapy for many years, is a drug that specifically inhibits the ability of the body to break down medicines,” said Barr. “The problem is that it’s incredibly non-specific. So there’s a whole host of medicines that people take, especially those medicines, unfortunately, that are associated with conditions that confer risk.”
A study published in the scientific journal Nature last week identified a “high overall frequency” of drug-to-drug interactions in high-risk Covid-19 patients in Spain treated with the antiviral drug lopinavir and ritonavir while in hospital. Such interactions were “alarmingly overlooked in the setting of the Covid-19 healthcare crisis,” concluded the authors of the study.
Pfizer said ritonavir has a well-characterised safety profile when used alone or in combination with other drugs. While it could result in drug interactions, these could be managed in many cases, it added.
“For drugs that share a common pathway for drug metabolism as Pfizer’s oral antiviral, over the five-day period of treatment, most patients would be able to dose-adjust down their medications, and then return to normal dosing after completing the oral antiviral regimen,” said a Pfizer spokeswoman.
The authorisation and commercial performance of molnupiravir is important for Merck, which unlike Pfizer did not develop a Covid-19 vaccine. If the FDA grants emergency use authorisation for the drug, the US government has a contract to buy 3.1m courses for $2.2bn.
Merck’s shares lost 17 per cent of their value over the past month following publication of data showing Pfizer’s antiviral pill Paxlovid is more effective than molnupiravir at reducing the risk of hospitalisation or death from Covid.
UK and EU regulators granted emergency use or conditional authorisation for the treatment last month.
However, the authorisations were granted before Merck published final clinical trial data showing the drug was 30 per cent effective at reducing the risk of hospitalisation and death in high-risk patients. This was sharply lower than the 50 per cent efficacy that Merck announced in October from a preliminary analysis of the data.
Last week Citi downgraded Merck from “buy” to “neutral”, noting the “clinical profile of [molnupiravir] continues to deteriorate”.
Barr at Merck said the safety profile of molnupiravir was “very strong” and many governments had expressed interest in acquiring supplies of it in order to combat Covid.