Chemical Name:Promethazine Hydrochloride

CAS：58-33-3

Synonyms:Phenergan (brand name); 10H-Phenothiazine-10-ethanamine, N,N,α-trimethyl-, monohydrochloride

Molecular Formula:C₁₇H₂₀N₂S·HCl

Molecular Weight:320.88 g/mol

Appearance:White to slightly yellow crystalline powder

Melting Point:221–225 °C (430–437 °F)

Solubility

- Freely soluble in water, ethanol, and chloroform

- Slightly soluble in acetone

- Insoluble in ether

pKa (Dissociation Constant):~9.1 (weak base)

Pharmacological Class:First-generation antihistamine (H? antagonist), phenothiazine derivative

Mechanism of Action:Blocks histamine H? receptors; strong sedative, antiemetic, and anticholinergic effects

Common Uses

- Allergy relief (e.g., hay fever, rash)

- Motion sickness and nausea/vomiting

- Sedation (preoperative or insomnia)

- Adjunct in cold/cough syrups

Stability Stable under normal conditions; protect from light and moisture

Safety Notes

- May cause drowsiness, dizziness, or dry mouth

- Contraindicated in children <2 years (respiratory depression risk)

- Avoid alcohol and CNS depressants

Promethazine Hydrochloride is a phenothiazine-derived antihistamine with potent sedative and antiemetic properties. Marketed under brands like Phenergan, it is widely used for allergies, nausea, and sedation. Its strong central nervous system (CNS) effects necessitate cautious dosing.