Efavirenz may be marketed under the name Sustiva, but generic versions are also available. It is taken in combination with other antiretroviral drugs.
Some drugs can interact with efavirenz and cause dangerous side-effects. Some examples are ergot alkaloids (used to treat migraine and cluster headaches and to control labour); midazolam (an anaesthetic); or St John's wort.
Some drugs can interact with efavirenz and change blood levels of one or both drugs, so dose adjustments may be needed. This is the case for the antiretroviral drugs ritonavir-boosted darunavir, lopinavir/ritonavir (Kaletra), ritonavir, ritonavir-boosted atazanavir and maraviroc. This is also the case for some drugs used to treat bacterial infections such as TB (including clarithromycin, rifabutin and rifampicin), anti-fungal treatments, anticonvulsants, statins, methadone, sertraline, calcium channel blockers, immunosuppressants and warfarin.
Efavirenz may reduce the effectiveness of some hormonal contraceptives (such as the pill, patches or an implant). If you are using this type of contraceptive to prevent pregnancy you should use an additional barrier method or a different type of contraception.
Resistance to efavirenz is likely to cause resistance to nevirapine and possibly to rilpivirine.
Severe rash, psychosis, suicidal feelings, liver failure.
Rash, itching, dizziness, headache, abnormal dreams, anxiety, depression, difficulty sleeping, disturbed concentration, diarrhoea, nausea, vomiting, abdominal pain, tiredness and raised triglyceride and liver enzyme levels.
Mood and sleep problems are most commonly experienced during the first four weeks of treatment and include feeling ‘out of sorts’, confusion, impaired concentration, sleep disturbance, abnormal dreams, anxiety and depression. In most cases these side-effects go away by themselves and it isn’t necessary to stop taking efavirenz. However, some people find them intolerable and need to change treatment as a result. If you have mental health problems, or have had in the past, efavirenz may not be a good choice for you. Talk to your doctor about other treatment options.
Take on an empty stomach. Some people find taking it with food reduces side-effects, but avoid taking it with a high-fat meal; this may increase absorption of the drug, potentially increasing side-effects. If efavirenz causes confusion or dizziness, taking the dose before going to bed can help reduce or prevent these side-effects.
The usual adult dose is one 600mg tablet taken once a day or three 200mg capsules taken once a day. Efavirenz is also available in a combination tablet with emtricitabine and tenofovir disoproxil. Efavirenz is available as a generic drug so appearances will vary.