Recently, the FDA issued an Emergency Use Authorization (EUA) for a new oral anti-viral agent for COVID-19 infection. This drug has limited availability. In Florida, the Department of Health has designated retail pharmacies in various counties in the state to fill prescriptions for the drug. The EUA is based on a study of about 2200 patients who were COVID positive. About 1100 got the drug, and about 1100 received a placebo. The patients in the study were at higher risk for progression of COVID to serious disease. Risk factors included a number of chronic diseases and age over 60. The average patient in the study was about 47. The study included 13% of patients over 65 and 3% of patients over 75.
Paxlovid is a two-drug combination. Nirmatrelvir is the drug that is active against COVID. The other component is Ritonavir, a drug used to treat HIV. Ritonavir is not active against COVID-19 but rather inhibits an enzyme that metabolizes Nirmatrelvir and renders it inactive. In essence, Rotonavir raises the blood level of Nirmatrelvir.
The enzyme that metabolizes Nirmatrelvir is called CYP3A. A number of drugs (some in common use and others not) can induce CYP3A or inhibit it. This makes prescribing a bit tricky. It requires a good drug history. The drug can not be used if the kidney function is moderately impaired (Creatinine clearance less than 30 ml/min). It can also not be used in severe liver disease. Treatment needs to be started within five days of symptom onset.
The drug seems to be well tolerated. More people stopped the drug in the placebo group than in the treatment group.
The drug reduced the risk of hospitalization and death by 88%!
Supplies of the drug are likely to be quite limited initially.