Section 11 · Monograph
Promethazine
Reviewed Nov 2026FDA label
PhenerganPhenothiazine antihistamine
- Forms
- Tab: 12.5, 25, 50mg | Supp: 12.5, 25, 50mg | IM/IV: 25mg/mL
- Dose
- 12.5-25mg q4-6h PRN
- MOA
- H1/D2/muscarinic blockade
Black Box Warning
- Severe tissue injury, including gangrene, can occur with injectable promethazine — deep intramuscular injection is preferred and subcutaneous or intra-arterial injection is contraindicated; IV use is discouraged
- Contraindicated in pediatric patients under 2 years of age because of fatal respiratory depression
Indications
- Allergic conditions, motion sickness, nausea and vomiting, preoperative sedation, adjunct to analgesicsFDA-labeled
Mechanism of Action
- Phenothiazine antihistamine with H1, dopamine D2 and muscarinic antagonist activity
Full Dosing
Adult / usual
- Nausea or vertigo: 12.5-25mg every 4-6 hours as needed, orally, rectally or by deep IM injection
- If IV use is unavoidable, dilute and give slowly into a large vein with a patent line
Contraindications
- Pediatric patients under 2 years of age
- Comatose states
- Hypersensitivity to phenothiazines
- Intra-arterial or subcutaneous injection
Drug Interactions
- Opioids and other CNS depressants: reduce doses
- Additive anticholinergic effects
- MAOIs may prolong and intensify effects
Adverse Effects
- Sedation and dizziness
- Anticholinergic effects
- Extrapyramidal reactions and neuroleptic malignant syndrome (rare)
- QT prolongation
- Tissue injury with injection
Monitoring Parameters
- Sedation and respiratory status
- IV/injection site
- Mental status in older adults
Pregnancy & Lactation
- Limited data; neonatal respiratory depression and withdrawal possible with late-pregnancy use
- Present in milk; use caution