Nucleoside/nucleotide analogue reverse transcriptase inhibitors (NRTIs/NtRTIs)

NRTIs/ NtRTIs are normally the basis or ‘backbone’ of any anti‑HIV drug combination. NRTIs may also be called nukes. The NRTIs are: 

• 3TC, lamivudine, Epivir 
• abacavir, Ziagen 
• AZT, zidovudine, Retrovir 
• d4T, stavudine, Zerit 
• ddI, didanosine, Videx, Videx EC 
• FTC, emtricitabine, Emtriva 
• tenofovir, Viread 

NRTI/NtRTI are also available in combination pills: 

• Combivir (3TC and AZT) 
• Kivexa (abacavir and 3TC) 
• Trizivir (3TC, AZT and abacavir) 
• Truvada (FTC and tenofovir) 

The two most common combinations of NRTI/NtRTI pills used are abacavir and 3TC (often given in the combined Kivexa formulation) and FTC and tenofovir (often given in the combined Truvada formulation). AZT and 3TC (usually combined as Combivir) is also widely used, but it should be noted that the use of AZT is discouraged because it has been shown to cause fat loss. 

NRTI/NtRTI/NNRTI combination pill: 

• Atripla (FTC, tenofovir and efavirenz) 

Non‑nucleoside reverse transcriptase inhibitors (NNRTIs)

An NNRTI is often taken with two NRTIs as first line HIV therapy. NNRTIs may also be called ‘non‑nukes’. 

Two NNRTIs are currently approved for use in the UK: 

• efavirenz, Sustiva 
• nevirapine, Viramune 

The NNRTI etravirine (TMC 125, Intelence) is expected to be approved in the UK and Europe in 2008. It has already been approved in the US. 

NNRTI/NRTI/NtRTI combination pill: 

• Atripla (efavirenz, FTC and tenofovir). 

Protease inhibitors (PIs)

The protease inhibitors in current use are: 

• atazanavir, Reyataz 
• darunavir, Prezista 
• fosamprenavir, Telzir 
• indinavir, Crixivan 
• lopinavir/ritonavir, Kaletra 
• nelfinavir, Viracept 
• ritonavir, Norvir 
• saquinavir, Invirase 
• tipranavir, Aptivus 

People who choose to take a combination containing a protease inhibitor almost always take a protease inhibitor ‘boosted’ by a small dose of ritonavir, as well as taking two NRTIs. Common ‘boosted’ protease inhibitors are: lopinavir/ritonavir (the only boosted protease inhibitor combination medicine), atazanavir/ritonavir, darunavir/ritonavir, fosamprenavir/ritonavir, indinavir/ritonavir, saquinavir/ritonavir and tipranavir/ritonavir.  

Other combinations may include one or two protease inhibitors, one NNRTI, and one or two NRTIs. If a person’s initial combination has not worked, some doctors may recommend a combination of four or more antiretrovirals. 

Fusion and entry inhibitors

Fusion inhibitors stop HIV from binding to and entering the human cell. One fusion inhibitor called T-20 (enfuvirtide, Fuzeon) has been approved and is given by a subcutaneous injection (similar to the way diabetics inject insulin). It is usually recommended to people who have been extensively pre‑treated with other anti‑HIV drugs and have very limited treatment options available to them. 

• T‑20, enfuvirtide, Fuzeon 

Entry inhibitors work by binding to a protein on the surface of HIV called CCR5. Once this has happened, HIV cannot attach to CD4 cells, meaning that the virus cannot infect human cells. One entry inhibitor, or CCR5 inhibitor, has been approved so far and others are in development. Their use is usually restricted to people who have been extensively pre‑treated with other anti‑HIV drugs and have very limited treatment options available to them. It’s also necessary for a person to have a test confirm that their HIV has the CCR5 co‑receptor. This test is called a tropism test. 

• maraviroc, Celsentri 

Integrase inhibitors

Integrase inhibitors stop HIV from integrating with human cells.  

• raltegravir (Isentress)  

The use of this drug is currently reserved for people who have been extensively pre-treated with other anti-HIV drugs and have very limited treatment options available to them.