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NNRTI (antiretroviral) Pregnancy: Should not be used during pregnancy unless the clinical condition requires it; perform pregnancy testing before initiation; barrier contraception plus another method, continued for 12 weeks after discontinuation. Retrospective reports of neural tube defects with first-trimester exposure (causal relationship not established). Breast-feeding not recommended (excreted in human milk; and women living with HIV are advised not to breast-feed).

Efavirenz

Brand names: Sustiva

Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI) used as part of combination antiretroviral therapy for HIV-1 infection.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Adults and adolescents over 40 kg: 600 mg orally once daily, in combination with nucleoside reverse transcriptase inhibitors (NRTIs) with or without a protease inhibitor.
Route: Oral (film-coated tablet), recommended on an empty stomach
Frequency: Once daily; bedtime dosing recommended to improve tolerability of nervous-system adverse reactions
Max: 600 mg once daily standard (up to 800 mg/day may be considered with rifampicin in patients >=50 kg)
Must always be given in combination with other antiretrovirals (never as monotherapy — rapid resistance). Efavirenz film-coated tablets are not suitable for children weighing less than 40 kg (hard capsules are available for these patients). Dose adjustment: with voriconazole, increase voriconazole maintenance to 400 mg every 12 h and reduce efavirenz by 50% (to 300 mg once daily), restoring the initial efavirenz dose when voriconazole stops. With rifampicin in patients weighing 50 kg or more, an increase to 800 mg/day may be considered. Mild liver disease: usual recommended dose with careful monitoring. Paediatric population: safety and efficacy not established in children below 3 months or weighing less than 3.5 kg.

Dose adjustments

Renal

Not studied in renal insufficiency, but <1% of a dose is excreted unchanged in urine so the impact on efavirenz elimination should be minimal.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Severe hepatic impairment (Child-Pugh Class C)
  • Co-administration with terfenadine, astemizole, cisapride, midazolam, triazolam, pimozide, bepridil or ergot alkaloids (e.g. ergotamine, dihydroergotamine, ergonovine, methylergonovine)
  • Co-administration with elbasvir/grazoprevir; herbal preparations containing St John's wort
  • Personal/family history of QTc prolongation or relevant arrhythmia risk, severe electrolyte disturbance, or concomitant QTc-prolonging (proarrhythmic) drugs (e.g. class IA/III antiarrhythmics, certain macrolides/fluoroquinolones/azole antifungals, methadone)

Side effects

  • Rash (most frequent; usually mild-to-moderate; severe blistering reactions, Stevens-Johnson syndrome and erythema multiforme reported)
  • Nervous system: dizziness, headache, somnolence, disturbance in attention, cerebellar coordination/balance disturbances (usually begin soon after onset and resolve over the first 2-4 weeks)
  • Psychiatric: abnormal dreams, anxiety, depression, insomnia; (uncommon) aggression, hallucination, psychosis, suicide attempt/ideation; (rare) completed suicide
  • Gastrointestinal: nausea; Metabolism: hypertriglyceridaemia (common), hypercholesterolaemia (uncommon)
  • General: fatigue; Immune: hypersensitivity (uncommon)

Interactions

  • CYP3A4 substrate/inducer: competition for CYP3A4 underlies the contraindicated co-administrations (terfenadine, astemizole, cisapride, midazolam, triazolam, pimozide, bepridil, ergot alkaloids)
  • Voriconazole: reduce efavirenz by 50% and increase voriconazole maintenance dose (see notes)
  • Rifampicin: consider increasing efavirenz to 800 mg/day in patients >=50 kg
  • Direct-acting antivirals not recommended with efavirenz: sofosbuvir/velpatasvir, velpatasvir/sofosbuvir/voxilaprevir, glecaprevir/pibrentasvir, elbasvir/grazoprevir (contraindicated)
  • St John's wort and Ginkgo biloba extracts not recommended (reduced efavirenz effect)

Clinical monograph

How it works

It non-competitively inhibits HIV-1 reverse transcriptase, preventing transcription of viral RNA into DNA and thereby suppressing viral replication.

Prescribing in practice

  • Central nervous system and psychiatric effects, including dizziness, abnormal dreams, mood changes, and depression with reports of suicidal ideation, are common and an important safety concern.
  • It is a cytochrome P450 inducer with numerous drug interactions and can prolong the QT interval.
  • It is typically taken once daily at bedtime to reduce the impact of central nervous system side effects, and food can increase exposure.

Monitoring

Monitor HIV viral load and CD4 count for response, alongside mood and neuropsychiatric symptoms and liver function.

Counselling the patient

  • Take at bedtime to lessen dizziness and vivid dreams, which often ease over the first weeks.
  • Report low mood or distressing thoughts promptly.
  • Take consistently every day to keep the virus suppressed.

Evidence & guidelines

Efavirenz has an extensive evidence base from randomised antiretroviral trials and long-standing inclusion in HIV treatment guidelines.

Reference: BHIVA HIV guidelines; EACS; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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