In this episode, I’ll discuss why you can’t use the Naranjo algorithm in the setting of drug overdose.
Shout out to “Toxicology Dave” on Twitter for highlighting this issue.
The Naranjo Adverse Drug Reaction Probability Scale (commonly referred to as the Naranjo Scale) attempts to apply objective criteria to answer the subjective question of whether or not an adverse reaction is likely caused by a medication a patient was taking at the time the reaction occurred.
The Naranjo algorithm assigns points to 10 questions about an adverse drug reaction. The points are then added and depending on the total the likelihood of the medication in question causing the ADR is judged to be definite, probable, possible or doubtful.
A Naranjo score is frequently included in reports of toxicology cases. However, the definition of adverse drug reaction that Naranjo and colleagues used in their validation of their scale specifically excludes intentional and accidental medication overdoses.
This definition excludes therapeutic failures, intentional and accidental poisoning, and drug abuse.
A review article published in 2013 highlighted the fact that over a dozen case reports of medication overdoses included a calculation of a Naranjo scale. The authors point out that:
Application of the Naranjo Scale in the overdose setting is not scientifically valid. Erroneous conclusions may be formed regarding treatment modalities when the Naranjo Scale is applied to events occurring in overdose patients.
A large concern highlighted in this article was that overdose treatment and resuscitative measures could be erroneously associated with adverse drug reactions, given the temporal relationship between their administration and clinical consequences of the overdose.
Since this review article was published, various case reports of medication overdoses continue to erroneously include the Naranjo scale as part of the assessment of the case report. One case of rhabdomyolysis after clozapine and benzodiazepine intoxication assigned a “probable” score to clozapine despite the fact that an equal score could have been attributed to the benzodiazepines ingested in the case.
“Toxicology Dave,” an emergency medicine physician and medical toxicologist indicated on Twitter that he has been asked to include the Naranjo Scale in case reports during the peer review process when submitting to medical journals.
From a toxicologist who has been made to calculate a Naranjo score by journal reviewers, be careful not to use this scale in overdose. The authors intentionally excluded its use in overdose. @MikeMullinsMD https://t.co/Ay36eazeHy
— Dave Liss (@dave_liss) May 22, 2020
Many pharmacists are likely to become journal reviewers as a result of ASHP residency preceptor requirements, and we are in a position to correctly apply scoring systems such as the Naranjo scale.
Members of my Hospital Pharmacy Academy have access to a practical training video on Understanding and Fulfilling ASHP Accreditation Requirements for Residency Preceptors, which includes an explanation of how to become a journal reviewer.
In addition there are trainings on Providing Feedback to Pharmacy Residents, Designing and Implementing a PGY-1 Rotation Experience, and Precepting Pearls for Residency Projects.
I’ve created this material as well as 100+ practical trainings and many more resources in the Academy to help hospital pharmacists learn practical critical care and hospital pharmacy skills and translate theoretical knowledge to the bedside. To get immediate access to everything the Academy has to offer go to pharmacyjoe.com/academy to join today.
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