Naranjo Adverse Drug Reaction Probability Scale

The Naranjo Adverse Drug Reaction Probability Scale is a widely used tool in pharmacovigilance for determining the likelihood that a specific drug causes an adverse drug reaction (ADR).

Developed in 1981, it helps standardize the assessment of drug-related adverse events, allowing healthcare professionals to assess the likelihood of causality.

How Naranjo Adverse Drug Reaction Probability Scale Works:

The Naranjo Algorithm consists of 10 questions that assess factors such as:

1. The timing of the drug administration and the adverse event.
2. Improvement of the adverse event after stopping the drug (dechallenge).
3. Recurrence of the event when the drug is reintroduced (rechallenge).
4. Alternative causes for the event.
5. Previous reports of similar reactions to the drug.

It helps in assessing causality by assigning a score based on a set of questions. The higher the score, the stronger the likelihood that the drug caused the adverse event.

The Naranjo Algorithm involves the following 10 questions, each with possible answers of “Yes,” “No,” or “Don’t Know,” which are assigned specific point values:

Naranjo Adverse Drug Reaction Probability Scale

To assess the adverse drug reaction, please answer the following and give pertinent score.

Question	Yes	No	Do Not Know	Score
1. Are there previous conclusive reports on this reaction?				0
2. Did the adverse event appear after the suspected drug was administered?				0
3. Did the adverse reaction improve when the drug was discontinued or a specific antagonist was administered?				0
4. Did the adverse reaction reappear when the drug was readministered?				0
5. Are there alternative causes (other than the drug) that could on their own have caused the reaction?				0
6. Did the reaction reappear when a placebo was given?				0
7. Was the drug detected in the blood (or other fluids) in concentrations known to be toxic?				0
8. Was the reaction more severe when the dose was increased, or less severe when the dose was decreased?				0
9. Did the patient have a similar reaction to the same or similar drugs in any previous exposure?				0
10. Was the adverse event confirmed by any objective evidence?				0

Calculate Score

Total Score: 0

Naranjo Algorithm Scoring:

• Definite ADR: ≥ 9 points
• Probable ADR: 5-8 points
• Possible ADR: 1-4 points
• Doubtful ADR: ≤ 0 points

These ranges refer to a scoring system often used in pharmacovigilance or clinical trials to assess the likelihood that an adverse drug reaction (ADR) is linked to a drug. The Naranjo Algorithm scoring criteria help classify ADRs into categories based on their likelihood, as follows:

1. Definite ADR (≥ 9 points):

• Description: The reaction is very likely to be caused by the drug.
• Characteristics:
  • A strong temporal relationship exists between drug administration and the onset of the ADR.
  • The reaction is well-known to be associated with the drug.
  • The ADR recurs on re-exposure to the drug (positive dechallenge and rechallenge).
  • Other possible causes for the reaction are ruled out.

2. Probable ADR (5-8 points):

• Description: The reaction is likely to be caused by the drug, though some uncertainty remains.
• Characteristics:
  • A clear temporal association is present, but the ADR does not necessarily recur upon re-exposure.
  • There may be other potential causes for the ADR, but the drug is the most plausible cause.
  • There is clinical evidence linking the drug to the ADR, but it may not be definitive.

3. Possible ADR (1-4 points):

• Description: There is a possible but uncertain link between the drug and the ADR.
• Characteristics:
  • A temporal relationship exists, but it’s weak or not clearly established.
  • Other causes for the reaction cannot be ruled out, and the drug is just one of several possibilities.
  • Clinical or experimental evidence is inconclusive or minimal.

4. Doubtful ADR (≤ 0 points):

• Description: It is unlikely that the drug caused the ADR.
• Characteristics:
  • The ADR does not have a strong temporal association with drug use.
  • There are other, more plausible explanations for the reaction.
  • There is little or no evidence linking the drug to the reaction, and the ADR could have occurred by chance or due to another cause.