Etravirine (Intelence)

Etravirine (Intelence) is an anti-HIV drug that reduces the amount of virus in the body and belongs to the class of drugs known as non-nucleoside reverse transcriptase inhibitors (NNRTIs). The enzyme reverse transcriptase converts single-stranded viral RNA into DNA. Drugs in the NNRTI class stop HIV from replicating within cells by binding near reverse transcriptase’s active site and inhibiting polymerase activity.

Formerly known as TMC-125, etravirine was developed by Tibotec Pharmaceuticals, Ltd. and is a diarylpyrimidine (DAPY), a different type of NNRTI specifically designed to be less susceptible than other NNRTIs to resistance mutations. As a flexible molecule, it can fit into different shaped binding pockets in the reverse transcriptase enzyme and this is why it remains active against HIV that is resistant to other NNRTIs.[ref]

Etravirine is indicated for treatment-experienced adults who have evidence of viral replication and HIV strains resistant to an NNRTI and other antiretrovirals. It should not be combined with licensed nucleoside analogues alone, due to the risk of virologic failure.

Etravirine is not recommended for use with an unboosted protease inhibitor, ritonavir-boosted atazanavir, fosamprenavir, or tipranavir. In addition, the manufacturer recommends resistance testing before initiating therapy with this drug.

Etravirine was approved in the US and European Union in 2008. Etravirine is marketed by Janssen, a subsidiary of Johnson & Johnson.

Effectiveness

Studies that led to the approval of etravirine showed that when combined with darunavir/ritonavir plus at least two nucleoside analogues selected by resistance testing, etravirine was significantly more effective than placebo in suppressing viral load in treatment-experienced people with at least one NNRTI resistance mutation and three or more primary protease inhibitor mutations.[ref] A subsequent study showed that etravirine was more effective in treatment-experienced people with fewer than three NNRTI mutations.[ref]

Despite its impressive activity against NNRTI-resistant HIV, those findings showed that the more NNRTI resistance mutations a person has, the lower the viral load reduction. Individuals with no NNRTI resistance mutations at baseline had a median viral load reduction of nearly 3 logs after 34 weeks of etravirine treatment combined with an optimised background regimen. Those with three or more NNRTI mutations had a viral load reduction of less than a log.

Side-effects

Although generally well tolerated in clinical trials, since the approval of etravirine, two types of severe reaction to the drug have been reported: toxic epidermal necrolysis (TEN) and drug rash with eosinophilia and systemic symptoms (DRESS).

Reported cases of these reactions developed between three and six weeks after treatment with the drug was started. In most cases, they disappeared when treatment with etravirine was stopped and therapy with corticosteroids was provided. Symptoms include rash, fever, general malaise, fatigue, muscle or joint aches, blisters, oral lesions, conjunctivitis, hepatitis, and high concentrations of a type of blood cell calls eosinophils.

In August 2009, the US Food and Drug Administration inserted a new warning to the package insert for etravirine (Intelence). It stated that severe cases of rash occurred in around 1.3% of people in phase 3 studies of the drug and 2% of people had to stop taking the drug due to serious rash, usually occurring in the first six weeks of treatment. In the most serious cases, people taking etravirine developed Stevens-Johnson syndrome or other severe skin reactions in which regions of the skin blister and peel away. It is expected that a similar warning will be added to European package inserts by the European Medicines Agency.

Glossary

non-nucleoside reverse transcriptase inhibitor (NNRTI)

Non-nucleoside reverse transcriptase inhibitor, the family of antiretrovirals which includes efavirenz, nevirapine, etravirine, doravirine and rilpivirine. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) bind to and block HIV reverse transcriptase (an HIV enzyme), preventing HIV from replicating.

resistance

A drug-resistant HIV strain is one which is less susceptible to the effects of one or more anti-HIV drugs because of an accumulation of HIV mutations in its genotype. Resistance can be the result of a poor adherence to treatment or of transmission of an already resistant virus.

mutation

A single change in gene sequence. Some HIV mutations cause the virus to become resistant to certain antiretroviral (ARV) drugs.

protease

An enzyme that HIV uses to break up large proteins into smaller ones from which new HIV particles can be made.

rash

A rash is an area of irritated or swollen skin, affecting its colour, appearance, or texture. It may be localised in one part of the body or affect all the skin. Rashes are usually caused by inflammation of the skin, which can have many causes, including an allergic reaction to a medicine.

People who develop a severe rash while taking etravirine were advised to seek immediate medical advice. If a hypersensitivity reaction to the drug is diagnosed, treatment with it should be stopped immediately. People who have stopped treatment due to hypersensitivity reactions should not restart therapy. 

Resistance

In contrast to other NNRTIs, more than one resistance mutation needs to develop, in order to bring about resistance to etravirine.[ref] [ref] The presence of the most common NNRTI mutation, K103N, did not affect the treatment response in individuals on etravirine in the DUET studies; however, the presence at baseline of V179D, V179F, V179T, Y181V, or G190S was associated with a decreased virologic response to etravirine.[ref] [ref]

Tibotec, manufacturer of etravirine, has noted that cross-resistance to efavirenz and/or nevirapine is to be expected after virologic failure while on an etravirine-containing regimen.

Drug interactions

Interactions with protease inhibitors complicate regimens containing etravirine. This is an especially important issue for a second-line NNRTI that may be used in third-line regimens with protease inhibitors.

Etravirine cannot be co-administered with boosted tipranavir/ritonavir (Aptivus), boosted fosamprenavir (Lexiva), full-dose ritonavir (Norvir 600mg), boosted atazanavir (Reyataz), unboosted protease inhibitors, and other NNRTIs.

Etravirine blood levels increase by 17% when prescribed with lopinavir (Kaletra). This combination may be used, but should be administered with caution. 

Because etravirine is such a potent inducer of the cytochrome p450 CYP3A4 pathway, it greatly speeds up the metabolism of the CCR5 antagonist maraviroc (Celsentri, Selzentry). Co-administration can reduce total maraviroc concentrations over a 12-hour period by 53% (AUC12) and peak levels of maraviroc (Cmax) by 60%.

Therefore, if an individual isn't also taking a potent CYP3A4 inhibitor such as a protease inhibitor, the recommended clinical dose for maraviroc alongside etravirine is 600mg twice daily. However, if maraviroc is being dosed alongside etravirine and darunavir together, a dose reduction to 150mg twice daily is necessary. Data showed no effect of maraviroc on etravirine pharmacokinetics, so no dose adjustment of etravirine is necessary.

Etravirine cannot be given with carbamazepine, phenobarbital, phenytoin, rifabutin (if part of a protease inhibitor/ritonavir containing-regimen), rifampin, rifapentine, or St John's wort (Hypericum perforatum). It does not appear to affect blood levels of methadone. Etravirine may reduce levels of clopidogrel.

Etravirine should be used with caution alongside fluconazole or voriconazole, because these drugs have the potential to raise etravirine levels.

The efficacy of etravirine and/or its side-effect profile can change when given with inhibitors, inducers, or substrates of CYP3A4, CYP2C9, and CYP2C19. Further information on drug interactions is available at www.intelence-info.com.

Taking it

The recommended oral dose of etravirine tablets is 200mg (two 100mg tablets) twice daily following a meal. Taking the drug on an empty stomach is not advised. For those who have difficulty swallowing, etravirine can be dissolved in water.

In 2008, the US manufacturer of etravirine stated that it should not be co-administered with atazanavir/ritonavir, fosamprenavir/ritonavir, or tipranavir/ritonavir.[ref]

Children

Etravirine is safe and effective in treatment-experienced children and adolescents. When combined with an optimised background regimen and dosed either by weight (5.2mg/kg) or 200mg twice a day etravirine suppressed viral load below 50 copies/ml in 56% of 101 children and adolescents.[ref]

Pregnancy

Etravirine has received only minimal study in pregnant women.

Laboratory studies in animals suggest that the drug is safe during pregnancy, and a case study has been presented of five pregnant women who received the drug through compassionate access due to limited options.[ref] Three of the women took therapy for their entire pregnancy, the other two during the third trimester only.

Monitoring of peak, trough and steady-state concentrations of etravirine showed that these were comparable to those seen in non-pregnant adults, suggested that no dose modification is necessary during pregnancy. None of their infants were infected with HIV. One infant was born with a minor abnormality to the right ear, but was healthy in all other respects. No birth abnormalities were observed in the other five babies. 

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