ADR Causality Assessment Scales

Naranjo Causality Scale (adapted)

1. Are there previous conclusive reports on this reaction?
Yes (+1) No (0) Do not know or not done (0)
2. Did the adverse event appear after the suspected drug was given?
Yes (+2) No (-1) Do not know or not done (0)
3. Did the adverse reaction improve when the drug was discontinued or a specific
antagonist was given?
Yes (+1) No (0) Do not know or not done (0)
4. Did the adverse reaction appear when the drug was readministered?
Yes (+2) No (-1) Do not know or not done (0)
5. Are there alternative causes that could have caused the reaction?
Yes (-1) No (+2) Do not know or not done (0)
6. Did the reaction reappear when a placebo was given?
Yes (-1) No (+1) Do not know or not done (0)
7. Was the drug detected in any body fluid in toxic concentrations?
Yes (+1) No (0) Do not know or not done (0)
8. Was the reaction more severe when the dose was increased, or less severe when the
dose was decreased?
Yes (+1) No (0) Do not know or not done (0)
9. Did the patient have a similar reaction to the same or similar drugs in any previous
exposure?
Yes (+1) No (0) Do not know or not done (0)
Scoring
· > 9 = definite ADR
· 5-8 = probable ADR
· 1-4 = possible ADR
· 0 = doubtful ADR

Naranjo et.al. Clin Pharmacol Ther. 1981 Aug;30(2):239-45



WHO Causality Assessment

Certain:
• Clinical event, lab test abnormality with plausible time relationship to drug intake
• Cannot be explained by concurrent disease or other drugs /chemicals
• Response to dechallenge- plausible
• Event must be definitive pharmacologically / immunologically
• Positive rechallenges (if performed).


Probable/ Likely:
• Clinical event, lab test abnormality with reasonable time relationship to drug intake
• Unlikely to be to concurrent disease, drugs / chemicals
• Clinically reasonable response to withdrawal (dechallenge)
• Rechallenge not required

Possible:
• Clinical event lab test abnormality with reasonable time relationship to drug intake
• Could also be explained by concurrent disease or other drugs or chemicals
• Information on drug withdrawal may be lacking or unclear

Unlikely:
• Clinical event , lab test with improbable time relationship to drug intake
• Other drugs , chemicals or underlying disease provide plausible explanations

Inaccessible /unclassifiable:
• Insufficient /contradictory evidence which cannot be supplemented or verified

Conditional / unclassified
• More data is essential for proper assessment or additional data are under examination