The Delta variant is a highly contagious Sars-CoV-2 virus strain. Video / Paul Slater
Pfizer says its antiviral Covid treatment Paxlovid cuts the chance of ending up in hospital or dying by 89 per cent.
What differentiates this from other medicines we have used since the start of the pandemic is it provides the opportunity for patients to be treated at home, witha combination of a capsule and a pill.
BREAKING: Another pill that people at high risk of severe Covid-19 would take at home to keep them out of the hospital could be on the horizon after Pfizer said its antiviral appeared to be 89% effective https://t.co/hm7Za6fu2d
The phase 2/3 trial data on which those hospitalisation rates are based have yet to be independently verified. Nor has the treatment been approved by any country for use outside a clinical trial.
Yet this development adds to our growing portfolio of potential options to directly target SARS-CoV-2, the virus that causes Covid-19, and to treat Covid symptoms.
Paxlovid is a combination of two different drugs – the HIV drug ritonavir (a capsule) and an experimental drug PF-07321332 (a pill).
Ritonavir protects the body from metabolising PF-07321332. It acts by being broken down by the body first (known as a sacrificial chemical) to ensure enough PF-07321332 reaches the virus intact.
PF-07321332 is a so-called protease inhibitor (as is ritonavir). It blocks the action of a vital enzyme (protease) and stops SARS-CoV-2 from making copies of itself.
What did the trial show?
The trial included 1219 "high risk" adults with Covid who were not in hospital. Each person had at least one characteristic or underlying medical condition associated with an increased risk of developing severe Covid. One group received the treatment, the other placebo.
The trial's interim results showed a reduction in the risk of hospitalisation or death by 89 per cent in the Paxlovid group compared to placebo.
At day 28, there were no deaths reported in the Paxlovid group, compared with 10 deaths in the placebo group. Side-effects were similar in both groups and were generally mild.
The company said the results were so promising it was recommended no new patients needed to be enrolled into the study. And the company was recommended to submit the data to the US Food and Drug Administration for emergency use approval.
One of several potential antiviral drugs
Paxlovid is one potential Covid drug for use at home. The idea is these could be prescribed at the first sign of infection to prevent serious illness and death. People would manage their own symptoms, monitored while at home, and only be transferred to hospital if their condition deteriorates.
Merck has its own antiviral drug, molnupiravir, also for home use. It's been approved for use in the UK, and is being considered for use in Australia.
UK becomes first to authorize Merck and Ridgeback Biotherapeutics' antiviral molnupiravir to treat mild-to-moderate Covid-19 https://t.co/E8yNb8sMkm
Then there's AstraZeneca's emerging Covid drug Evusheld. Australia's Therapeutic Goods Administration (TGA) has just given this "provisional determination", meaning the company can now submit data for evaluation.
Evusheld contains two long-acting monoclonal antibody drugs – tixagevimab and cilgavimab. It's an injection that could be given in hospital or as an outpatient to prevent infections from getting worse.
Human trials have shown when Evusheld was used before exposure to Covid, there were significantly fewer symptoms.
Although Evusheld may potentially be used to prevent Covid, it would not be a substitute for vaccination. But it could provide additional protection for people who may have an inadequate response to vaccination or who cannot be immunised.
AstraZeneca’s new Covid treatment Evusheld could offer higher protection against variants and help vulnerable people ward off the virus. https://t.co/e3Rd3cHKQn
There are several steps before we can routinely expect to take Covid drugs at home to prevent the worst of the symptoms. We need independent verification of these drugs' efficacy and safety, and of course, regulatory approval.
Australia has ordered about 800,000 doses of antiviral drugs as I recall. But these are not yet available and we don't know when they will be in doctor's clinics or when they will be approved for use. They are also very expensive. Get the vaccine! https://t.co/WuyWDY8p2X
Developing new medicines, particularly at the pace required because of Covid, means these new drugs aren't cheap. One consideration for state and federal governments will be balancing the costs of the medicines against health outcomes.
The daily cost of a patient in hospital in Australia is around A$5000 (NZ$5208) for an uncomplicated (non-Covid) admission. This is much more than the reported cost of a full course of molnupiravir to the US government at US$700 (about NZ$994).
But the costs of Paxlovid, and other new Covid medicines, have not been released and may be very much higher than the hospital costs.
The Conversation
Nial Wheate is an associate professor at the Sydney Pharmacy School, University of Sydney; Elise Schubert is a pharmacist and PhD candidate at the University of Sydney.
