Chemical Name:Promethazine Hydrochloride
CAS：58-33-3
Synonyms:Phenergan (brand name); 10H-Phenothiazine-10-ethanamine, N,N,α-trimethyl-, monohydrochloride
Molecular Formula:C<sub>17</sub>H<sub>20</sub>N<sub>2</sub>S·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 (H₁ antagonist), phenothiazine derivative
Mechanism of Action:Blocks histamine H₁ 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.
| Test Item | Specification | Test Method |
|---|
| Appearance | White to slightly yellow crystalline powder | Visual inspection (EP/USP) |
| Identification | Complies with IR, HPLC, or TLC comparison | USP <621>, EP 2.2.24 (HPLC) |
| Assay (Purity) | 98.0%–101.0% (anhydrous basis) | USP <621> (HPLC/Titration) |
| Water Content | ≤0.5% | USP <921> (Karl Fischer) |
| Residue on Ignition | ≤0.1% | USP <281> (Sulfated ash) |
| Heavy Metals | ≤10 ppm (e.g., Pb, Cd, Hg) | USP <232>/ICP-MS |
| Related Substances | Individual impurity ≤0.5%, Total ≤1.0% | HPLC (USP <621>) |
| Chloride Content | 10.8%–11.6% (as HCl) | Argentometric titration |
| pH (1% Solution) | 4.5–6.0 | USP <791> (pH meter) |
| Melting Point | 221–225°C | USP <741> (Capillary method) |
| Microbial Limits | TAMC ≤1000 CFU/g, TYMC ≤100 CFU/g | USP <61>, EP 2.6.12 |
| Dissolution (Tablets) | ≥80% released in 30 min (if applicable) | USP <711> (Paddle method) |
| Specific Rotation | -0.10° to +0.10° (20°C, 1% in water) | USP <781> (Polarimetry) |
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