Names: Cobicistat, Tybost

Approved dosage: Cobicistat is a boosting agent available as a 150mg tablet (Tybost) for boosting of darunavir or atazanavir, or incorporated in several products:

• Evotaz (atazanavir/cobicistat)
• Rezolsta (darunavir/cobicistat)
• Stribild (elvitegravir/cobicistat/tenofovir disoproxil/emtricitabine)
• Genvoya (elvitegravir/cobicistat/tenofovir alafenamide/emtricitabine
• Symtuza (darunavir/cobicistat/tenofovir alafenamide/emtricitabine).

Common side-effects: Raised blood sugar, increased appetite, difficulty in sleeping, drowsiness, abnormal dreams, headache, dizziness, altered sense of taste, nausea, diarrhoea, abdominal pain, bloating, flatulence, dry mouth, jaundice, rash, and tiredness.

Rare side-effects: Kidney stones

Key drug interactions: As a boosting agent, cobicistat can also interact with other medicines. See drug interaction information for the agents listed above for specific drug interaction information.

Cobicistat should not be used with alfusozin, ranolazine, dronedarone,carbamazepine, phenobarbital, phenytoin, rifampicin, lurasidone pimozide, dihydroergotamine, ergotamine, cisapride, lovastatin, simvastatin, triazolam or oral midazolam.

Names: Ritonavir, RTV, Norvir

Approved dosage: Ritonavir was one of the first protease inhibitors developed, but is no longer used as an anti-HIV drug due to its side-effects.  However, it is given at very low doses (too low for anti-HIV effects) to ‘boost’ the level of other PIs such as darunavir and atazanavir. When used for its boosting effects, the dose of ritonavir is usually 100mg or 200mg once or twice daily (depending on the frequency with which you take the protease inhibitor it is boosting).

Tips on taking it: Take with food to reduce nausea. Do not chew, break or crush tablets. Ritonavir tablets and the powder for oral suspension should always be stored at room temperature.

Common side-effects (at low dose): Raised lipid levels, diarrhoea.

Rare side-effects: Changes in heart rhythm, severe allergic (hypersensitivity) reaction and rash (Stevens-Johnson syndrome).

Key drug interactions: See the section on protease inhibitors for more information on possible interactions.

Ritonavir interacts with many other medications. Consult your doctor or HIV pharmacist before taking any other drugs with ritonavir or a ritonavir-boosted drug (including steroid-containing inhalers, nasal sprays, eye drops, creams, as well as medicines bought from a high-street chemist, herbal preparations and recreational drugs).