In this episode, I’ll discuss treating diphenhydramine overdose in the absence of physostigmine.
The usual antidote for anticholinergic drug toxicity is physostigmine, however it is no longer available in the US. Even though the FDA has authorized the importation of an equivalent product, pharmacists may face the need to treat a patient for anticholinergic toxicity without access to this antidote.
That is exactly what happened to a group of clinicians who published a case report in Pharmacotherapy of how they treated a patient with a massive diphenhydramine overdose without using physostigmine.
The case is that of a 21-year-old female with confirmed diphenhydramine overdose of 3600 mg. While in the ED, the patient experienced hallucinations, attempted to remove monitoring systems, struck a nurse, and repeatedly yelled incoherently. Physostigmine would normally have been used but it was unavailable to the clinicians due to the shortage situation. The patient was vomiting, so the oral route for cholinesterase inhibitors like rivastigmine was not feasible. Instead of using oral rivastigmine, a 9.5 mg rivastigmine patch was applied to the patient on her back-left shoulder area where the patient could not remove it. After just 4 hours from when the patch was applied, the patient’s mental status improved, and vomiting subsided.
The authors emphasize that rivastigmine remains a pharmacodynamically based, clinically reasonable, and underutilized option for managing anticholinergic delirium, and that the transdermal route of administration can be considered when the oral route is not an option and IV physostigmine is not readily available
The article in this episode is a selection from my Hospital Pharmacy Academy’s weekly literature digest. Have you ever felt like your physician colleagues are one step ahead of you with new literature developments? Every week, Academy members are provided a summary curated and explained by me of the top hospital pharmacy-related articles published that week from over 20 major journals and sources to save you time and keep you up to date with the literature. To get immediate access, go to pharmacyjoe.com/academy.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.
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