Efavirenz
Efavirenz is an antiviral drug, according to the US prescribing information for efavirenz tablets. It is used in combination with other antiretroviral agents for the treatment of HIV-1 infection in adults and in children at least three months old and weighing at least 3.5 kg. MedlinePlus’s drug information on efavirenz covers the medicine for patients in more detail.
Key points
- In vitro studies suggest that CYP3A and CYP2B6 are the major isozymes responsible for efavirenz metabolism, and efavirenz has been shown in vivo to induce these enzymes, increasing the breakdown of other drugs metabolised the same way.
- Time to peak plasma concentrations is approximately 3 to 5 hours, with steady-state plasma concentrations reached in 6 to 10 days.
- In controlled trials, central nervous system symptoms were reported in patients treated with efavirenz tablets, including dizziness in 28.1%, insomnia in 16.3%, impaired concentration in 8.3%, somnolence in 7.0%, abnormal dreams in 6.2% and hallucinations in 1.2% of the 1,008 patients.
- Rashes linked to efavirenz are usually mild to moderate maculopapular skin eruptions that begin within the first 2 weeks of starting treatment, with a median time to onset of 11 days, and in most patients who continue treatment the rash resolves within 1 month, with a median duration of 16 days.
Safety specific to Efavirenz
Efavirenz tablets must not be used as a single agent to treat HIV-1 infection, or added on as a sole agent to a failing regimen. Resistant virus emerges rapidly when efavirenz is administered as monotherapy.
Serious psychiatric adverse experiences have been reported in patients treated with efavirenz tablets.
QTc prolongation has been observed with the use of efavirenz. The label advises considering alternatives to efavirenz when it would be coadministered with a drug that carries a known risk of Torsade de Pointes, or when given to a patient who is otherwise at higher risk of Torsade de Pointes.
A smaller number of patients experience more severe skin reactions: rash with blistering, moist desquamation or ulceration occurred in 0.9% of patients treated with efavirenz tablets, and the label reports a 0.1% incidence of Grade 4 rash, such as erythema multiforme or Stevens-Johnson syndrome. Efavirenz tablets are contraindicated in anyone with previously demonstrated clinically significant hypersensitivity, such as Stevens-Johnson syndrome, erythema multiforme or toxic skin eruptions, to any of its components. Coadministration of efavirenz with elbasvir and grazoprevir is also contraindicated.
Efavirenz may cause fetal harm when administered during the first trimester to a pregnant woman. Females of reproductive potential who are receiving efavirenz tablets are advised to avoid pregnancy.
Postmarketing cases of hepatitis, including fulminant hepatitis progressing to liver failure requiring transplantation or resulting in death, have been reported in patients treated with efavirenz. Efavirenz is not recommended for patients with moderate or severe hepatic impairment.