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. 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.

Apart from Kaletra, which has ritonavir included in the formulation, other boosted PIs need ritonavir to be dosed as a spearate 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 for using therapeutic drug monitoring (TDM).

Lopinavir/r (Kaletra) is the most widely used PI.

Fosamprenavir/r is an alternative to Kaletra that is used less frequently.

Atazanavir/r is a once-daily PI. It is not approved in Europe for first-time therapy, but is still used widely for this. Atazanavir/r is recommended if you want to switch drugs because of side effects. The daily dose is 300mg, boosted by 100mg of ritonavir.

If this dose causes side-effects, the ritonavir can sometimes be stopped and a slightly higher atazanavir dose (400mg) used instead. A recent study suggested you get better drug levels with unboosted atazanavir by taking 200mg twice-daily.

Unboosted atazanavir should not be used in a combination that includes tenofovir.

Darunavir/r is a PI used for secondline PI therapy. However, a recent study showed that darunavir achieved better results compared to Kaletra in people using treatment for the first time. Guidelines may therefore recommend darunavir for first-line treatment in the future.

Saquinavir/r is an alternative to Kaletra that is used less frequently.

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

Nelfinavir is not recommended in UK guidelines for first-line therapy but it is sometimes chosen as the third drug if someone cannot tolerate ritonavir or for use during pregnancy.