Diphenhydramine injection
BENADRYL IM / IV
What it isInjectable H1 and muscarinic antagonist; allergic reactions and acute dystonia or parkinsonism.
Why this oneThe B-52 ingredient: anticholinergic cover against haloperidol dystonia while it sedates.
What limits itSedation, delirium, urinary retention, and hypotension make its anticholinergic burden especially hazardous in older adults.
FDA-approved for
- anaphylaxis adjunct / allergic reactions (~1946)
- dystonia / parkinsonism (~1946)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Allergic reactions/anaphylaxis adjunct, motion sickness, parkinsonism (when oral impractical) | Adults | 10–50 mg IV/IM (up to 100 mg if required) | 400 mg/day | |
| Allergic reactions, motion sickness, parkinsonism (when oral impractical) | Pediatric (not neonates/premature infants) | 5 mg/kg/day or 150 mg/m²/day IV/IM divided into 4 doses | 300 mg/day |
Renal Undefined.
Hepatic Undefined.
Instructions
- IV or IM only; IV rate generally not exceeding 25 mg/min
- Administer deep intramuscularly
- Do not use subcutaneously/intradermally (risk of necrosis)
Contraindications
- Use in neonates or premature infants
- Use in nursing mothers
- Use as a local anesthetic (risk of local necrosis)
Cautions
- Caution in narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal/bladder-neck obstruction, prostatic hypertrophy
- Overdose in pediatrics may cause hallucinations, convulsions, death
- More sedation/dizziness/hypotension in the elderly
Adverse reactions
- Sedation/sleepiness
- Dizziness
- Hypotension
- Dry mouth/nose/throat
- Tachycardia
- Thickening of bronchial secretions
- Urinary retention
Pregnancy Undefined.
Lactation Contraindicated in nursing mothers (higher antihistamine risk for infants).
NO BOXED WARNINGS
Principal riskAnticholinergic burden; on every elderly deprescribing list
Classes and tags
Clinical profile
Mechanism of action: Diphenhydramine injection ballicule
