Drug reaction phenotypes & approach
Reaction phenotype → timing → management approach, per the 2022 Drug Allergy Practice Parameter.
Evidence tier: Guideline-derived.
| Phenotype | Timing | Usual approach |
|---|---|---|
| Benign delayed maculopapular rash | >6 h to days | Risk stratify; often direct or graded oral challenge if low risk |
| Immediate urticaria / anaphylaxis | Minutes to ~1-6 h | Skin testing where validated; graded challenge if negative; desensitization if needed and likely allergic |
| SCAR (SJS/TEN/DRESS/AGEP) | Days–weeks (DRESS 2-8 wk) | Absolute lifelong avoidance; a NEGATIVE test does NOT clear; HLA screening (B*57:01/abacavir, B*15:02 or A*31:01/carbamazepine, B*58:01/allopurinol); no routine challenge |
| Infusion reaction | During infusion | Slow infusion / premedication / graded escalation vs desensitization, by mechanism and severity |
| NSAID cross-intolerant (NERD/NECD/NIUA) | Minutes–hours after COX-1 NSAID | Avoid strong COX-1 inhibitors; COX-2 inhibitors generally tolerated; aspirin desensitization for AERD/need |
| Single-NSAID reaction (SNIUAA) | Variable | NOT cross-reactive, tolerates structurally unrelated NSAIDs; do not globally label "NSAID-allergic" |
Notes
- Drug challenge (provocation) is the gold standard for most antibiotic evaluation; single-dose or 2-step graded challenges are preferred over old multistep protocols in low-risk patients.
- Distinguish predictable (type A) reactions and intolerance (e.g., vancomycin flushing = infusion-rate, not IgE) from true allergy and delabel them.
- Penicillin–cephalosporin cross-reactivity is ~2-3% and follows R1 side-chain similarity, not the legacy ~10%.
Evidence & citations
Clinician decision support. Verify against the cited source. Not a substitute for clinical judgment. 100% on-device; no patient data is stored or transmitted.