Efavirenz is an antiretroviral medication classified as a non-nucleoside reverse transcriptase inhibitor (NNRTI). It is used to treat infection with human immunodeficiency virus (HIV). The drug is available in pill form at strengths of 200 mg and 600 mg. In Hong Kong, efavirenz is a prescription-only medication and is regulated by the Department of Health in line with international standards such as those set by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA).
Efavirenz works by binding directly to the HIV-1 reverse transcriptase enzyme. This binding blocks the enzyme’s ability to convert viral RNA into DNA, a critical step in the HIV replication cycle. By stopping this conversion, efavirenz reduces the amount of virus that can infect new cells, helping to lower viral load and preserve immune function.
Key pharmacologic characteristics include:
Efavirenz is approved for use in combination with other antiretroviral agents to treat HIV-1 infection in adults and adolescents. In Hong Kong, the approved indications align with those of the FDA and EMA:
Efavirenz is not indicated for prevention of HIV infection (pre-exposure prophylaxis) or for use in patients with documented hypersensitivity to the drug.
Efavirenz induces several CYP enzymes, notably CYP3A4, CYP2B6, and CYP2C9, which can lower plasma concentrations of co-administered drugs.
Major interactions:
Decreases concentrations of protease inhibitors (e.g., atazanavir, lopinavir/ritonavir).
Reduces effectiveness of hormonal contraceptives - alternative non-hormonal methods should be considered.
Moderate interactions:
May lower levels of certain antiepileptics (e.g., phenytoin) and anticoagulants (warfarin).
May increase concentrations of drugs metabolised by CYP2C19 (e.g., clopidogrel).
Patients should provide a complete medication list, including over-the-counter products and herbal supplements, before starting efavirenz.
If a dose is missed, take it as soon as remembered unless it is close to the time of the next scheduled dose. Do not double the dose.
Symptoms may include severe CNS depression, seizures, or respiratory compromise. Seek emergency medical care immediately; supportive measures and monitoring are the primary treatment.
Efavirenz does not require tapering. However, abrupt cessation can lead to viral rebound and resistance. Any change in therapy should be supervised by a qualified healthcare professional.
This article provides educational information about efavirenz and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
Efavirenz is intended to be part of a combination regimen that typically includes two nucleoside reverse transcriptase inhibitors (NRTIs). This combination maximises viral suppression and reduces the chance of resistance. Always follow the prescriber's specific regimen plan.
Taking efavirenz at night can lessen the impact of its common central nervous system side effects, such as vivid dreams and insomnia, because sleep may mask these symptoms.
Yes. Efavirenz induces enzymes that lower the effectiveness of hormonal contraceptives (pills, patches, rings). Women using efavirenz should discuss alternative or additional non-hormonal birth control methods with their provider.
A severe or spreading rash may indicate a serious allergic reaction (e.g., Stevens-Johnson syndrome). Seek immediate medical attention, as discontinuation of the drug may be required.
Patients with mild to moderate hepatic impairment can often use efavirenz, but clinicians usually monitor liver enzymes closely and may adjust the regimen if abnormalities develop.
Yes, but keep medication in its original labelled container, carry a copy of your prescription, and be aware of any country-specific import restrictions for antiretroviral drugs. Always have a supply that covers the entire trip plus extra days.
Acetaminophen generally does not interact with efavirenz. Non-steroidal anti-inflammatory drugs (NSAIDs) are also safe, but patients with liver disease should use caution with high-dose acetaminophen.
Efavirenz penetrates the central nervous system and can alter neurotransmitter activity, leading to changes in sleep architecture and vivid dreaming. These effects usually lessen after several weeks of therapy.
Yes. Several manufacturers produce generic efavirenz tablets that meet the same quality standards as the branded product. Availability may vary by pharmacy.
Both belong to the NNRTI class, but newer agents may have fewer central nervous system side effects and a different resistance profile. Choice of therapy depends on individual patient factors, resistance testing, and physician judgment.
