# HIV Protease Inhibitors

> HIV protease inhibitors for MBBS Pharmacology — ritonavir boosting, atazanavir jaundice, indinavir stones and metabolic toxicity.

- Canonical URL: https://prepelephant.com/topics/mbbs/pharmacology/hiv-protease-inhibitors
- Exam / course: MBBS · Subject: Pharmacology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "HIV Protease Inhibitors", PrepElephant, https://prepelephant.com/topics/mbbs/pharmacology/hiv-protease-inhibitors

## Direct answer

HIV protease inhibitors block the viral aspartyl protease that cleaves the gag-pol polyprotein, so virions assemble but remain immature and non-infectious. Members include atazanavir, darunavir, lopinavir and the boosting agent ritonavir, whose ferocious CYP3A4 inhibition raises levels of partner drugs. Their burden is metabolic — lipodystrophy, hyperlipidaemia and insulin resistance — together with a web of drug interactions that disqualify simvastatin and rifampicin.

## What you must remember

- Mechanism: transition-state analogues occupy the protease active site, preventing post-translational cleavage of viral precursors; the result is structurally defective, non-infectious particles.
- Ritonavir boosting: even low-dose ritonavir inhibits CYP3A4 so profoundly that it pharmacokinetically boosts atazanavir, darunavir or lopinavir, allowing lower doses and longer intervals — lopinavir-ritonavir was the fixed-dose mainstay of Indian programmes.
- Darunavir boosted with ritonavir or cobicistat is the preferred protease inhibitor for treatment-naive and experienced patients, owing to its high genetic barrier.
- Signature toxicities: indinavir — crystalluria, nephrolithiasis and unconjugated hyperbilirubinaemia; atazanavir — benign indirect hyperbilirubinaemia with jaundice and cholelithiasis; darunavir — rash and hepatotoxicity.
- Class metabolic syndrome: peripheral fat wasting with central accumulation, hypertriglyceridaemia, insulin resistance and new-onset diabetes, plus transaminase elevation.
- Interactions dominate prescribing: simvastatin and lovastatin are contraindicated; rifampicin is avoided with protease inhibitors, using rifabutin instead in tuberculosis coinfection; doses of warfarin, steroids and antiarrhythmics spiral unpredictably.
- All are heavily protein-bound, and boiled down to exam essence: protease inhibitors are inhibitors of cytochrome P450 that act as victims and perpetrators of interactions in both directions.

## Common confusion

Ritonavir's role confuses students most: at boosting doses it contributes little antiviral activity and exists purely to inhibit CYP3A4 and raise companion drug levels. The second muddle is treating atazanavir jaundice as hepatotoxicity — it is benign unconjugated hyperbilirubinaemia from bilirubin glucuronidation inhibition that mimics Gilbert syndrome, not liver injury.

## Exam-focused takeaway

Theory answers should explain gag-pol cleavage blockade, ritonavir-boosting logic, the metabolic toxicity cluster and interaction rules. Viva examiners ask why rifampicin and protease inhibitors clash and how tuberculosis-HIV coinfection is handled. MCQs test mechanism, indinavir stones, atazanavir jaundice, contraindicated statins and lipodystrophy.

## Frequently asked questions

### How do protease inhibitors render HIV non-infectious?

By inhibiting the viral protease that cleaves gag-pol polyproteins, so progeny virions are produced with immature cores unable to complete the replication cycle.

### Why is ritonavir given in small doses with other protease inhibitors?

It inhibits CYP3A4-mediated metabolism so strongly that partner drug exposure rises, allowing lower doses, longer dosing intervals and a higher genetic barrier to resistance.

### Which protease inhibitor causes renal stones?

Indinavir, through crystalluria and stone formation — one reason it has disappeared from routine use.

### Why does atazanavir cause jaundice?

It inhibits hepatic glucuronidation of bilirubin, producing reversible unconjugated hyperbilirubinaemia and clinical jaundice without liver damage.

### Which drugs are contraindicated with protease inhibitors?

Simvastatin and lovastatin, risking rhabdomyolysis, and rifampicin, which collapses protease inhibitor levels — alternatives like pravastatin and rifabutin are used instead.