Promethazine

PHENERGAN

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Pronunciation: proe-METH-a-zeen

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

Promethazine PHENERGAN mascot mnemonic cartoon — Visual mnemonic: Promethazine 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 isFirst-generation antihistamine with dopamine antagonism; nausea, vertigo and allergy.

Why this oneIt covers both histaminergic and dopaminergic nausea, which ondansetron does not.

What limits itSevere tissue injury including gangrene if it extravasates — the IV route is avoided. Contraindicated under age 2; strongly sedating and anticholinergic.

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

Promethazine prescription history

Animated chart of estimated U.S. prescriptions per year, Antiemetics (1946–2026). Promethazine enters in 1951 (estimated).

FDA-approved for

nausea/allergy (~1951)

Off-label

insomnia
migraine

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 Contraindicated in children under 2 years of age due to potential for fatal respiratory depression.

FDA dosing	Population	Start	Target	Max
Allergy	Adult	25 mg QHS (or 12.5 mg before meals + QHS; or 6.25-12.5 mg TID)	lowest effective	per response
Motion sickness	Adult	25 mg BID (first dose 0.5-1 h before travel)
Motion sickness	Pediatric (≥2 yr)	12.5-25 mg BID
Nausea and vomiting	Adult	25 mg, repeat q4-6h PRN
Nausea and vomiting	Pediatric (≥2 yr)	0.5 mg/lb, adjusted to age/weight
Sedation	Adult	12.5-25 mg QHS

Renal Undefined

Hepatic Undefined

Nausea/vomiting doses may be repeated q4-6h PRN

Instructions

Contraindicated under 2 years of age
Use lowest effective dose; caution with concomitant respiratory depressants
Do not use antiemetics for vomiting of unknown etiology in children/adolescents

Available strengths

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

Contraindications

Children under 2 years of age
Comatose states
Hypersensitivity/idiosyncratic reaction to promethazine or other phenothiazines
Treatment of lower respiratory tract symptoms including asthma

Cautions

Respiratory depression, potentially fatal in young children
Neuroleptic malignant syndrome
Sedation; additive CNS/respiratory depression
Extrapyramidal symptoms; lowers seizure threshold
Paradoxical hyperexcitability

Adverse reactions

Drowsiness, sedation, dizziness
Blurred vision, dry mouth
Extrapyramidal symptoms (oculogyric crisis, torticollis, tongue protrusion)
Respiratory depression/apnea (potentially fatal)
Leukopenia, thrombocytopenia, agranulocytosis
Neuroleptic malignant syndrome

Pregnancy Use only if potential benefit justifies risk; given within 2 weeks of delivery may inhibit newborn platelet aggregation

Lactation Undefined

Cost

Promethazine (PHENERGAN)

What pharmacies pay · NADAC 9/30/26

Strength		#/mo	generic $/mo	CostPlus
12.5 mg	tab	30 qd	$1.63	offered
25 mg	tab	30 qd	$1.36	offered
50 mg	tab	30 qd	$2.46	offered

Other forms: Promethazine injection (PHENERGAN IM)

Generic entry1982

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Self-check

Promethazine: Which parenteral route is avoided because of tissue injury?
IV.
Promethazine: Below what age is it contraindicated?
2 years.