Promethazine injection

PHENERGAN IM

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Pronunciation: proe-METH-a-zeen

Promethazine injection ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Promethazine injection ballicule

Promethazine injection PHENERGAN mascot mnemonic cartoon — Visual mnemonic: Promethazine injection mascot
**“Finnegan’s Prom hazing”**
hazing of Finnegan at prom
purple drank, a.k.a. Sizzurp, a concoction of promethazine/codeine syrup mixed with Sprite

What it isInjectable H1, muscarinic, and dopamine antagonist; allergy, nausea, and procedural sedation.

Why this oneIt combines antihistamine, antiemetic, and sedative effects in one parenteral agent.

What limits itSevere tissue injury, including gangrene and amputation, can occur regardless of route; deep IM is preferred. It can fatally depress breathing in children under 2.

Promethazine injection molecular structure (skeletal formula) — Molecular structure: Promethazine injection

FDA-approved for

allergic conditions / nausea / sedation (~1956)

Classes and tags

Clinical profile

Therapeutic safety burden1 / 4

Overdose danger2 / 4

Weight-gain liability1 / 4

Sedation liability3 / 4

QT / Torsades2 / 4

Direct muscarinic antagonism3 / 4

Embryofetal risk1 / 4

Legacy pregnancy categoryC

Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.

FDA label

Read the full label on DailyMed ↗

BOXED WARNING Respiratory depression in pediatrics (contraindicated <2 years; fatal respiratory depression); severe tissue injury including gangrene with any parenteral route (IV >1 mg/mL, intra-arterial, and subcutaneous routes contraindicated).

FDA dosing	Population	Start	Target	Max
Allergic conditions	Adults		25 mg IM; may repeat within 2 h if needed
Sedation (hospitalized)	Adults		25–50 mg IM
Nausea and vomiting	Adults		12.5–25 mg IM, not repeated more often than every 4 h
Pre-/postoperative adjunct	Adults		25–50 mg IM (with reduced analgesic/atropine-like doses)
Obstetric sedation (labor)	Adults	50 mg IM (early labor)	25–75 mg (avg 50 mg) in established labor; may repeat at 4 h intervals	100 mg/24 h in labor
Sedation/allergic/antiemetic (various)	Children ≥2 yr		Should not exceed half the adult dose; premedication 1.1 mg/kg

Renal Undefined.

Hepatic Use cautiously in impaired liver function.

Instructions

Preferred route is deep intramuscular; avoid SC and intra-arterial
IV only after dilution, at ≤1 mg/mL, into a large/central vein over 20–40 min
Discontinue infusion immediately if injection-site pain occurs

Available strengths

inj 25, 50 mg/mL
tab 12.5, 25, 50 mg
sol 6.25 mg/5 mL
supp 12.5, 25, 50 mg

Contraindications

Pediatric patients less than 2 years of age (fatal respiratory depression)
Intravenous injection at concentrations greater than 1 mg/mL
Intra-arterial injection
Subcutaneous injection
Comatose states

Cautions

Respiratory depression (avoid in compromised respiratory function/COPD/sleep apnea)
Severe tissue injury/gangrene
CNS depression/sedation
Extrapyramidal symptoms
Anticholinergic effects
Avoid in suspected Reye's syndrome

Adverse reactions

Drowsiness/sedation
Respiratory depression
Severe tissue injury (burning, necrosis, gangrene)
Extrapyramidal symptoms
Blood pressure changes
Dry mouth

Pregnancy Undefined.

Lactation Undefined.

Cost

Promethazine injection (PHENERGAN IM)

What pharmacies pay · NADAC 9/30/26

Strength		#/mo	generic $/unit	CostPlus
25 mg/mL	inj	per unit	$1.54/mL	not offered
50 mg/mL	inj	per unit	$2.34/mL	not offered

Other forms: Promethazine (PHENERGAN)

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Self-check

Promethazine injection: Which injection route is preferred?
Deep IM.
Promethazine injection: Can severe tissue injury occur despite route choice?
Yes; regardless of route.