Naranjo ADR Probability Scale

Adverse Drug Reaction Probability Scale — Naranjo et al., 1981

Purpose
Standardised causality assessment: estimates the probability that a clinical event (e.g. a cutaneous eruption) is an adverse reaction to a specific suspected drug.
Population
Any patient with a suspected adverse drug reaction. Score each suspected drug separately. Not designed for severe cutaneous reactions with specific instruments (use ALDEN for SJS/TEN, RegiSCAR for DRESS).
Formula
Sum of 10 weighted items (yes / no / do not know), range −4 to +13.
Categories
Definite ≥ 9 · Probable 5–8 · Possible 1–4 · Doubtful ≤ 0 (Naranjo 1981).
❓ Questionnaire

Answer each question for the suspected drug. "Do not know" also covers tests not done.

📋 Categories — reference
Definite
≥ 9
Reaction followed a plausible temporal sequence, with positive dechallenge and rechallenge (or toxic drug levels), and could not be explained by the patient's condition or other drugs.
Probable
5 – 8
Reasonable temporal sequence, improvement on withdrawal, not explained by the patient's condition; rechallenge not available.
Possible
1 – 4
Reasonable temporal sequence, but could be explained by the patient's condition or other drugs; dechallenge information lacking or unclear.
Doubtful
≤ 0
The event is more likely related to factors other than the suspected drug.
📚 References
  1. Naranjo CA, Busto U, Sellers EM, et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther. 1981;30(2):239–45.
  2. Sassolas B, Haddad C, Mockenhaupt M, et al. ALDEN, an algorithm for assessment of drug causality in Stevens-Johnson syndrome and toxic epidermal necrolysis: comparison with case-control analysis. Clin Pharmacol Ther. 2010;88(1):60–8.
  3. Kardaun SH, Sekula P, Valeyrie-Allanore L, et al. Drug reaction with eosinophilia and systemic symptoms (DRESS): an original multisystem adverse drug reaction. Results from the prospective RegiSCAR study. Br J Dermatol. 2013;169(5):1071–80.
Clinical decision support only. This tool is intended to assist clinical assessment and does not replace professional judgment. Always interpret results in the context of the individual patient.