Ritonavir

Ritonavir is an antiretroviral drug that inhibits HIV protease. It is also used at low doses to slow the metabolism of other antiviral medicines and increase their blood levels.

HIV protease: An HIV enzyme that cleaves viral polyproteins into functional proteins needed for viral maturation. Ritonavir directly inhibits this enzyme, preventing production of mature infectious HIV particles.
Combination antiretroviral therapy: HIV treatment using multiple antiretroviral drugs that target different stages of viral replication. Ritonavir is used in multidrug regimens rather than as a stand-alone HIV treatment.
Cobicistat: A pharmacokinetic enhancer that inhibits CYP3A enzymes but has no direct antiviral activity. Cobicistat boosts selected antiretrovirals without ritonavir’s own HIV protease inhibition.
Cytochrome P450: A family of enzymes that metabolizes drugs and other compounds, especially in the liver and intestine. Ritonavir’s inhibition of CYP3A4 is one instance of drug effects on this enzyme family.
CYP3A4: A cytochrome P450 enzyme that metabolizes many drugs, especially in the intestine and liver. Ritonavir inhibits CYP3A4, slowing the breakdown of co-administered antivirals.
Lopinavir/ritonavir: A fixed-dose combination of two HIV protease inhibitors used in antiretroviral treatment. Ritonavir boosts lopinavir exposure in this established combination.
Darunavir: An HIV protease inhibitor used with other antiretroviral drugs to treat HIV infection. Darunavir is a boosted protease inhibitor, while ritonavir commonly serves as its booster.
Ritonavir drug interactions: Clinically significant changes in drug exposure caused by ritonavir’s inhibition of drug-metabolizing enzymes and transporters. Its booster effect can complicate treatment with medicines that share metabolic pathways.
Pharmacokinetic enhancer: A drug used to alter another medicine’s absorption, distribution, metabolism, or elimination and thereby change its exposure. This broader role explains why ritonavir is prescribed at low doses alongside other antivirals.
Nirmatrelvir/ritonavir: An oral COVID-19 treatment combining the SARS-CoV-2 protease inhibitor nirmatrelvir with ritonavir. Ritonavir slows nirmatrelvir metabolism so antiviral concentrations remain higher for longer.

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