Primovir is an antiviral medication that combines two separate medications. When you take your three-pill dose, two of them will be nirmatrelvir, which inhibits a key enzyme required by the viral infection virus to produce functional virus particles. The viral infection virus that is released from the cells is no longer able to enter uninfected cells in the body after nirmatrelvir treatment, which effectively ends the infection. The other is ritonavir, a drug that was previously used to treat HIV/AIDS but is now used to increase the effectiveness of antiviral medications.
As a viral infection treatment, ritonavir essentially shuts down nirmatrelvir's metabolism in the liver, so it doesn't leave your body as quickly, allowing it to work longer and help fight the infection.