Activated Charcoal in Diphenhydramine Toxicity
Yes, activated charcoal is appropriate for diphenhydramine toxicity when administered within 1 hour of ingestion in patients with an intact or protected airway, though it should not be given en route to the emergency department due to the risk of rapid deterioration. 1
Key Clinical Decision Points
Timing and Administration
- Administer activated charcoal within 1 hour of diphenhydramine ingestion for maximum benefit, as effectiveness decreases significantly after this window 2
- The standard adult dose is 50g (or 1 g/kg body weight) administered orally or via nasogastric tube 3, 4
- For children under 6 years, use only non-sorbitol-containing formulations to avoid hypernatremic dehydration 5
Critical Contraindications Specific to Diphenhydramine
Do not administer activated charcoal en route to the emergency department because diphenhydramine can cause rapid onset of altered consciousness or seizures, creating aspiration risk 1. This is a unique consideration for antihistamine toxicity that differs from other poisonings.
Airway Protection Requirements
- Activated charcoal is absolutely contraindicated when airway protective reflexes are impaired unless the airway is secured 5, 2
- Diphenhydramine specifically causes loss of consciousness and seizures, making airway assessment critical before any charcoal administration 1
Clinical Algorithm for Decision-Making
Step 1: Assess timing
- If >4 hours post-ingestion with no symptoms: Do not refer to ED, charcoal not indicated 1
- If <1 hour post-ingestion: Charcoal strongly indicated if other criteria met 2
- If 1-4 hours post-ingestion: Consider charcoal but benefit uncertain 2
Step 2: Evaluate airway status
- Any altered consciousness beyond mild drowsiness: Secure airway first, then consider charcoal 1, 2
- Symptoms warranting immediate ED referral WITHOUT charcoal en route: agitation, staring spells, hallucinations, abnormal muscle movements, loss of consciousness, seizures, or respiratory depression 1
Step 3: Confirm toxic dose
- Children <6 years: ≥7.5 mg/kg warrants ED referral and charcoal consideration 1
- Patients ≥6 years: ≥7.5 mg/kg or 300 mg (whichever is less) warrants ED referral and charcoal consideration 1
Important Caveats
Pre-Hospital Setting
- Never induce emesis in diphenhydramine poisoning 1
- Activated charcoal should not be administered by EMS personnel en route due to the unpredictable rapid onset of CNS depression and seizures specific to antihistamines 1
- This differs from other poisonings where pre-hospital charcoal may be appropriate 6
In-Hospital Administration
- In volunteer studies, activated charcoal effectively adsorbs diphenhydramine when given early 7
- Sorbitol-containing formulations showed preserved adsorption capacity for diphenhydramine in vitro and in vivo, but use cautiously due to dehydration risk with repeated doses 7, 3
Common Pitfall
The most critical error is administering activated charcoal to a patient with diphenhydramine toxicity who has subtle early anticholinergic symptoms (mild agitation, confusion) without recognizing that rapid deterioration to seizures or coma can occur, leading to aspiration 1. When in doubt about mental status, secure the airway first 2.