Starting on a boosted PI

Although UK guidelines recommend starting with an NNRTI-based combination, PI-based combinations can be just as good at getting your viral load to undetectable.

PI regimens can be less vulnerable to resistance if you have problems with adherence.

Some people start on a PI regimen and then switch to an NNRTI regimen that requires fewer pills later.

UK guidelines only recommend using ritonavir-boosted PIs (written PI/r where the ‘r’ stands for ritonavir).

Apart from Kaletra, which has ritonavir included in the formulation, other boosted PIs need ritonavir to be dosed as a separate pill.

• Using a small dose of ritonavir in these combinations provides better and more sustained drug levels. This reduces the risk of resistance. It also reduces the numbers of pills and dietary requirements compared to unboosted PIs.
• Ritonavir boosting reduces the risk of resistance. It also reduces the numbers of pills and dietary requirements compared to unboosted PIs.
• Some people find even small doses of ritonavir increase nausea.
• Some people who are very sensitive to ritonavir side effects can use unboosted PIs (usually nelfinavir or atazanavir), but they need to confirm drug levels using therapeutic drug monitoring (TDM).

Lopinavir/r (Kaletra) is a widely used PI. It is approved as a twice-daily drug. The main side effects include lipid changes, nausea and diarrhoea.

Atazanavir/r is a once-daily PI. Atazanavir/r is often recommended if you want to switch drugs because of side effects from efavirenz. The daily dose is 300mg, boosted by 100mg of ritonavir.

UK guidelines in 2010 may include atazanavir/r as a first-line option based on recent study results.

If this dose causes side-effects, the ritonavir can sometimes be stopped and a slightly higher atazanavir dose (400mg) used instead.

Unboosted atazanavir can be taken as 200mg twice-daily, but you would need to have your drug levels measured.

Unboosted atazanavir should not be used in combination with tenofovir.

Darunavir/r is a mainly used as a twice-daily PI in second-line therapy. Once-daily dosing (800/100mg) is approved in Europe as a first-line treatment in people starting their first treatment.

UK guidelines in 2010 may include darunavir/r as a first-line option based on recent study results.

Saquinavir/r and fosamprenavir/r are alternative options that are prescribed less frequently.

Tipranavir/r is a PI that is only used by people with PI-resistance.

Nelfinavir is rarely used now because it is less effective than recent drugs. It remains an option if someone cannot tolerate ritonavir.