A 38-year-old man with HIV-1 infection on efavirenz-based antiretroviral therapy (EFV + 2 NRTIs) presents with persistent neuropsychiatric symptoms (dizziness, nightmares, impaired concentration) after 2 weeks of therapy. Which feature best distinguishes efavirenz from integrase strand transfer inhibitors (INSTIs) in this clinical context?

Explanation

## Distinguishing Feature: CNS Toxicity Profile ### Efavirenz (NNRTI) **Key Point:** Efavirenz is notorious for **dose-dependent CNS adverse effects** due to high CSF penetration and lipophilicity. - CNS penetration: ~50% of plasma concentration in CSF - Neuropsychiatric side effects: dizziness, nightmares, impaired concentration, depression, psychosis - Symptoms typically occur in first 2–4 weeks (as in this case) - Dose-dependent: higher plasma levels → worse CNS toxicity - Occurs in 40–50% of patients; often resolves with continued therapy - Lipophilic and crosses blood–brain barrier readily ### Integrase Strand Transfer Inhibitors (INSTIs) **Key Point:** INSTIs (dolutegravir, bictegravir, cabotegravir) have **minimal CNS penetration** and **negligible neuropsychiatric toxicity**. - Poor CNS penetration due to substrate for efflux transporters (P-gp, BCRP) - Excellent tolerability with rare CNS side effects - No dose adjustment needed for CNS toxicity - Preferred in patients with psychiatric comorbidities ### Comparison Table | Feature | Efavirenz | INSTIs (e.g., Dolutegravir) | | --- | --- | --- | | **CNS penetration** | High (~50% CSF:plasma) | Low (efflux transporter substrate) | | **Neuropsychiatric toxicity** | Common (40–50% of patients) | Rare (<5%) | | **Onset of CNS effects** | 2–4 weeks | Not applicable | | **Lipophilicity** | High | Moderate | | **Metabolism** | CYP3A4 and CYP2B6 | UGT1A1 (minimal CYP interactions) | | **Drug interactions** | Extensive | Minimal | | **Preferred in psychiatric patients** | No | Yes | **High-Yield:** Efavirenz's **high CNS penetration and lipophilicity** make it the NNRTI most associated with neuropsychiatric side effects—a defining and clinically important distinction from INSTIs, which are now preferred first-line agents partly because of their superior tolerability. **Mnemonic:** **EFV = Effects on brain** (Efavirenz = Frequent neuropsychiatric effects) **Clinical Pearl:** This patient's symptoms (dizziness, nightmares, impaired concentration at 2 weeks) are classic for efavirenz toxicity. Switching to an INSTI-based regimen (e.g., dolutegravir + 2 NRTIs) would likely resolve these symptoms while maintaining viral suppression. **Tip:** In NEET PG exams, when comparing efavirenz to modern agents (INSTIs, integrase inhibitors), the question almost always hinges on **CNS toxicity** — efavirenz's Achilles heel. [cite:Harrison 21e Ch 197]