Protease inhibitors are a distinct class of HIV medicine that acts at the final stage of the viral life cycle. Darunavir and atazanavir are the best known members used in HIV care, and both are given alongside a booster such as ritonavir. This guide explains how the class works, what boosting means, and where protease inhibitors fit in treatment today.
The class is often abbreviated to PIs, and a boosted combination is usually written with a slash, for example darunavir/ritonavir.
| Important note This article is general information about medicines used in HIV care. It does not include dosing instructions and is not a substitute for medical advice. All HIV medicines are prescription-only and are selected, started, and changed by a qualified doctor. |
Quick Summary / Key Takeaways
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Protease inhibitors are a distinct class of HIV medicine that acts at the final stage of the viral life cycle. Darunavir and atazanavir are the best known members used in HIV care, and both are given alongside a booster such as ritonavir. The class is often abbreviated to PIs.
Protease is an enzyme HIV uses at the end of its life cycle, cutting long protein chains into the pieces needed to assemble new, infectious viral particles. Protease inhibitors block that enzyme. New particles are still produced, but they cannot mature into a form capable of infecting other cells.
Protease inhibitors are cleared from the body quickly on their own. A booster slows that clearance so the medicine remains at effective levels. Ritonavir is the most commonly used booster, and cobicistat serves a similar purpose. When ritonavir is used this way, it is not acting as the main treatment medicine. This mechanism also explains why the class is closely reviewed for interactions, as covered in drug interactions with ART.
| Medicine | Where it fits |
|---|---|
| Darunavir (with ritonavir) | Named the preferred protease inhibitor in current guidance |
| Atazanavir (with ritonavir) | A long established option, used where suitable |
| Lopinavir (with ritonavir) | An earlier option, now used more selectively |
| Ritonavir | Used as a booster rather than as the main treatment medicine |
This class is mainly used when a regimen is being changed rather than for people starting treatment. Guidance updated in January 2026 recommends darunavir with ritonavir as the preferred protease inhibitor where a change is needed. The wider context is covered in second-line ART and when to switch.
| Myth | Fact |
|---|---|
| Ritonavir is the main treatment medicine in these combinations. | In this role ritonavir acts as a booster, not the main medicine. |
| Protease inhibitors work at the same stage as NRTIs. | They act at the final stage, preventing new particles maturing. |
| This class is used for everyone starting treatment. | It is mainly used when a regimen is being changed. |
| Yellowing with atazanavir always signals liver harm. | It commonly reflects a harmless rise in bilirubin, but needs medical review. |
| Boosting simply means a stronger dose. | Boosting slows clearance so levels remain effective. |
| When to Consult a Doctor Medical advice is appropriate before starting or changing a protease inhibitor, where digestive effects persist, where yellowing of the skin or eyes appears, and whenever another medicine is being started. A consultation can be arranged through an HIV doctor consultation. |
Protease inhibitors block the enzyme HIV needs to assemble mature, infectious particles, and are given with a booster so they remain at effective levels. Darunavir with ritonavir is named the preferred option in current guidance. The class is used mainly when treatment is being changed, always under medical direction.
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Protease inhibitors are a class of HIV medicine that blocks protease, the enzyme HIV uses to assemble new infectious particles. Blocking it means new particles cannot mature.
Protease inhibitors are cleared from the body quickly on their own. A booster such as ritonavir slows that clearance so the medicine stays at effective levels. In this role ritonavir is not the main treatment medicine.
Guidance updated in January 2026 recommends darunavir with ritonavir as the preferred protease inhibitor where a change of regimen is needed.
This class is mainly used when a regimen is being changed rather than for people starting treatment, where integrase inhibitor regimens are preferred.
Reported effects include nausea, loose stools and other digestive effects, changes in cholesterol and lipid measures, headache, and tiredness. With atazanavir, some people notice yellowing of the skin or eyes.
This commonly reflects a rise in bilirubin, which is generally harmless in this context. It should still be reviewed by the treating doctor.
Boosted regimens affect how the body processes a wide range of medicines, which is why the treating doctor reviews everything being taken.
Ritonavir belongs to the protease inhibitor class, but in modern regimens it is used at booster level to raise the levels of another protease inhibitor rather than acting as the main treatment medicine.
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