Boosted PIs (PI/b): darunavir or atazanavir

Darunavir is the most widely used PI in the UK. Atazanavir is still sometimes used. Both are usually boosted by either ritonavir or cobicistat. Sometimes atazanavir can be used unboosted.

Side effects from ritonavir and cobicistat include stomach upset, diarrhoea, nausea and increases in lipids. This is why PIs are not always a preferred first choice.

The booster ensures better and more constant drug levels of the PI and this reduces the risk of drug resistance, but PIs still need to be taken with food. Also, boosters interact with other meds including inhaled, injectable, nasal sprays and topical steroids.

Ritonavir or cobicistat can be given as separate pills. There are also single pill versions of atazanavir/cobicistat (Evotaz) and darunavir/cobicistat (Rezolsta).


Darunavir is mainly used once-daily (unless there is extensive PI resistance)

Darunavir is generally easy to tolerate and fewer people switch than with atazanavir.  Side effects include rash, nausea, diarrhoea, lipid changes and a higher risk of heart disease, especially with long-term use.

The single pill versions of darunavir/cobicistat is called (Rezolsta).


Atazanavir is a once-daily PI that is used less often because of a side effect that can make skin and eyes look yellow. This is reversible if the drug is changed.

Atazanavir has an important drug interaction with over-the-counter antacid drugs including PPIs (proton pump inhibitors) and others.

The single pill versions of atazanavir/cobicistat is called Evotaz.

Last updated: 1 October 2019.