Guanosine‑analogue NRTI used in combination antiretroviral therapy. After intracellular phosphorylation to the triphosphate, it competitively inhibits HIV reverse transcriptase and causes DNA chain termination.
Widely used NRTI backbone option. Unique risk of a potentially fatal hypersensitivity reaction strongly associated with HLA‑B*57:01; patients must be screened before starting therapy.
Used as part of 2‑NRTI backbone (often with lamivudine) plus an integrase inhibitor.
Pre‑treatment HLA‑B*57:01 testing documented before dispensing.
Hypersensitivity usually within the first 2–6 weeks: fever, malaise, GI upset (nausea, abdominal pain), ± rash, and respiratory symptoms (dyspnea, cough).
Class effects of NRTIs: mitochondrial toxicity → lactic acidosis/steatosis (rare).
Always verify HLA‑B*57:01 is NEGATIVE before initiating; if positive, choose another NRTI (e.g., tenofovir).
If hypersensitivity is suspected: STOP abacavir immediately; symptoms typically resolve after discontinuation; NEVER re‑challenge.
Consider cardiovascular risk profile—some data link abacavir exposure with higher MI risk; prefer alternatives in patients with high ASCVD risk when options exist.
Hepatic metabolism (alcohol dehydrogenase/glucuronidation) → avoid in significant hepatic impairment; no renal adjustment needed.
NNRTI with vivid dreams, CNS effects, and rash/hepatotoxicity (not HLA‑B*57:01–specific).
Indication: part of combination ART for HIV‑1/2.
Dosing: typically once daily in fixed‑dose combinations (e.g., with lamivudine).
Monitoring: document negative HLA‑B*57:01, counsel on early hypersensitivity symptoms, monitor liver enzymes and for lactic acidosis if symptomatic.
Mnemonic: ABC = Always Be Checking HLA‑B*57:01 first.
Hypersensitivity often mimics viral syndrome; presence of fever + GI ± respiratory symptoms after starting ART is a red flag.
Do not confuse with sulfa allergy; mechanism is T‑cell–mediated, allele‑restricted—re‑exposure can be life‑threatening.
Suspected abacavir hypersensitivity → permanent discontinuation; re‑exposure may cause rapid, fatal reactions.
Do not start in patients who are HLA‑B*57:01 positive or with a prior history of abacavir hypersensitivity.
Before starting ART: order HLA‑B*57:01 test.
If positive → avoid abacavir; select alternative NRTI.
If negative → initiate abacavir‑containing regimen with counseling about early symptoms.
If fever ± GI/respiratory symptoms or rash within 2–6 weeks → stop abacavir immediately → switch regimen → document allergy; never re‑challenge.
New ART start; 10 days later develops fever, nausea, abdominal pain, and shortness of breath with a diffuse rash. Best next step → stop abacavir; never re‑challenge.
HIV patient with strong family history of early MI—choose NRTI backbone avoiding abacavir due to potential CV risk signal.
Question asks which pre‑treatment test is required before ABC initiation → HLA‑B*57:01 genotyping.
Case 1
A 32‑year‑old with newly diagnosed HIV begins abacavir/lamivudine + dolutegravir. Ten days later, she develops fever, malaise, nausea, and dyspnea; exam shows a faint maculopapular rash.
Case 2
A 55‑year‑old man with HIV, prior MI, and LDL 170 mg/dL is starting ART. HLA‑B*57:01 is negative.
