Diphenhydramine is commonly involved in overdose or misused. Although it is primarily used for its anti-histamine property, it also has significant antimuscarinic effect.

A recent retrospective study investigated the clinical characteristics associated with severe outcomes in diphenhydramine overdose using the multi-center Toxicology Investigators Consortium (ToxIC) Registry. 

Severe outcomes were defined as any of the following:

• Seizure
• Ventricular dysrhythmia
• Intubation

 

Results

863 cases of isolated diphenhydramine ingestion were identified between Jan 1, 2010 to Dec 31, 2016

• Females: 59.1% 
• Age < 18 years: 51.3%
• Intentional ingestion: 86.0%
  • Self-harm: 37.5%
  • Abuse/misuse: 11.5%

Most common symptoms:

• Delirium/toxic psychosis: 40.1% (n=346)
• Agitation: 33.1% (n=286)
• Severe outcome: 15.6% (n=135)

Factors associated with severe outcome

• Intubation: self-harm ingestion and male
• Acidemia: pH <7.2
• QRS prolongation: QRS > 120 msec
• Elevated anion gap: AG >20

Conclusion

• Acidemia, QRS prolongation and elevated anion gap was associated with severe outcome in diphenhydramine toxicity

References

Hughes AR et al. Clinical and patient characteristics associated with severe outcome in diphenhydramine toxicity. Clin Toxicol (Phila) 2021.

https://doi.org/10.1080/15563650.2021.1892716