The Naranjo Adverse Drug Reaction Probability Scale
Anything applied to the skin or taken by mouth has the potential to cause a side effect. Some medications rarely cause side effects and others tend to cause frequent side effects. Occasionally a patient will report a side effect that perhaps has never been reported before. The question then becomes - is this a real side effect from the drug or is it happening from something else?
In my clinic, the cause and effect relationship of a drug and a side effect become relevant in a wide range of situations. Common examples include:
- Did the drug my doctor prescribed me cause my hair loss?
- Did the drug given for my hair loss cause me to develop this side effect I am worried about (fatigue, muscle pain, leg twitching, abnormal blood tests)?
A Closer Look at the Naranjo Adverse Drug Probability Scale
The Naranjo Scale was created nearly 40 years ago to help standardize how clinicians to about assessing whether or not a drug could be implicated in an adverse drug reaction. It is used in controlled clinical trials. The scale is quite easy to use - and involves asking the patient 10 questions. Answers to the question are recorded as "yes", "no" or "don't know" and different points are assigned to each answer (-1, 0, +1, +2).
Typical Questions in the Naranjo Scale
- Are there previous conclusive reports of this reaction?
- Did the adverse event appear after the drug was given?
- Did the adverse reaction improve when the drug was discontinued or a specific antagonist was given?
- Did the adverse reaction reappear upon readministering the drug?
- Were there other possible causes for the reaction?
- Did the adverse reaction reappear upon administration of placebo?
- Was the drug detected in the blood or other fluids in toxic concentrations?
- Was the reaction worsened upon increasing the dose? Or, was the reaction lessened upon decreasing the dose?
- Did the patient have a similar reaction to the drug or a related agent in the past?
- Was the adverse event confirmed by any other objective evidence?
Determining the Naranjo Score
Scores can range from -4 to + 13. A score of 0 or less means the likelihood of the drug causing the side effect is doubtful, a score 1 to 4 indicates it is 'possible', a score 5 to 8 means it is 'probable' and a score 9 to 13 means it is 'definite'
Calculating the Naranjo Score
The website http://www.pmidcalc.org/index.php provides a free online calculator for clinicians to calculate the Naranjo Score. It is easy to use and has been embedded below as an example. Individuals wanting to know if a specific drug caused hair loss should be sure to speak to their dermatologist.
Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Vancouver office at 604.283.9299