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Causality: well established
Causality assessment · Causality: well established
Abacavir and Hypersensitivity reaction: is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Abacavir ↔ Hypersensitivity reaction
n=200 co-reports · PRR 3.8 · ROR 3.9
Abacavir causes a potentially life-threatening hypersensitivity reaction — fever, rash, gut and breathing symptoms that worsen with each dose and can be fatal on rechallenge — and this reaction is strongly tied to the HLA-B*57:01 genetic marker. Because screening for that allele before starting the drug nearly eliminates the risk, abacavir is one of the clearest examples of pharmacogenomic testing preventing a serious adverse reaction. The 200 co-reports (PRR 3.8) reflect both the real effect and the drug's use in HIV therapy.
Regulatory basis: abacavir prescribing information (boxed warning for hypersensitivity; HLA-B*57:01 screening; never rechallenge).
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Reaction appears within weeks of starting and is severe on rechallenge |
| Strength | partial | PRR 4 on a modest co-report count |
| Consistency | met | Reproduced and mechanistically linked to HLA-B*57:01 |
| Specificity | met | A highly distinctive abacavir reaction |
| Biological gradient | partial | Determined by genotype rather than dose |
| Plausibility | met | HLA-B*57:01-restricted T-cell activation is the mechanism |
| Coherence | met | Coheres with the boxed warning and mandatory genetic screening |
| Experiment | met | Genetic screening (a controlled intervention) prevents it — a real-world experiment |
| Analogy | met | Analogous to other HLA-linked drug hypersensitivities (carbamazepine, allopurinol) |
This page's own qualitative read, not an automated/citation-gated assessment.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for abacavir captured the hypersensitivity reaction as a coded event; the risk and its HLA-B*57:01 basis were established through genetics and screening trials rather than a standard AE table.