Promethazine Hydrochloride

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Cat Number

API0231865

CAS Number

58-33-3

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CAS Number

58-33-3

EINECS

200-375-2

Synonyms

Promethazine HCl; Dimethyl-(1-methyl-2-phenothiazin-10-ylethyl)amine hydrochloride

Molecular Formula

C17H21ClN2S

Molecular Weight

320.88

Smiles

CC(CN1C2=CC=CC=C2SC3=CC=CC=C31)N(C)C.Cl

Appearance

White to faint yellow powder

Melting Point

230-240°C

Boiling Point

430.7℃

General Description

Promethazine hydrochloride is a phenothiazine derivative antihistamine with potent sedative, antiemetic, and anticholinergic properties. As a first-generation H1 receptor antagonist, promethazine is classified as a prescription medication requiring careful patient monitoring due to its central nervous system depressant effects and potential for respiratory depression, particularly in pediatric populations.

Mechanism of Action

Promethazine exerts its pharmacological effects primarily through selective blockade of peripheral H1 histamine receptors, thereby antagonizing histamine-mediated allergic responses. It also blocks central histaminergic receptors in the reticular system, producing dose-dependent sedation and hypnosis. Additionally, promethazine possesses centrally acting anticholinergic properties and inhibits the medullary chemoreceptive trigger zone, which mediates its antiemetic effects. Unlike antipsychotic phenothiazines, it exhibits minimal dopamine receptor antagonism.

Application

Promethazine hydrochloride is indicated for multiple clinical scenarios including seasonal allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis, urticaria, and angioedema. It is widely used for preoperative, postoperative, and obstetric sedation, prevention and control of nausea and vomiting, treatment of motion sickness, and as adjunctive therapy to analgesics for pain management.

Kasai T, et al. investigated whether promethazine hydrochloride (PH) could prevent fatty degeneration in skeletal muscle, a condition that contributes to weakness and loss of function. Using human PDGFRα-positive mesenchymal progenitors, the researchers found that PH inhibited adipogenesis in a dose-dependent manner without cytotoxicity. This effect was mediated through suppression of phosphorylation of cAMP response-element binding protein, a key regulator of adipogenesis. In a mouse model of tendon rupture with intramuscular fat deposition, PH treatment significantly suppressed ectopic adipocyte formation derived from PDGFRα+ cells.

Fig. 1 Drug repositioning (DR) using human platelet-derived growth factor receptor α (PDGFRα)+ cells identifies promethazine hydrochloride (PH) as an adipogenesis-inhibiting drug. (Kasai T, et al., 2017)

References

Kasai T, et al. Promethazine Hydrochloride Inhibits Ectopic Fat Cell Formation in Skeletal Muscle. Am J Pathol. 2017;187(12):2627-2634.

Whitmore CA, et al. reported the development and validation of a novel carbon-11 labeled promethazine positron emission tomography (PET) radioligand for imaging amyloid-beta (Aβ) pathology in Alzheimer's disease. The probe was synthesized with high radiochemical purity (>95%) and molar activity (48 TBq/μmol). Specificity for Aβ binding was demonstrated through autoradiography using human hippocampal tissue.

Fig. 2 Design and synthesis of PMZ and a precursor for the synthesis of [11C]PMZ radioligand. (Whitmore CA, et al, 2021)

References

Whitmore CA, et al. Design, Synthesis, and Validation of a Novel [11C]Promethazine PET Probe for Imaging Abeta Using Autoradiography. Molecules. 2021;26(8):2182.

Does Promethazine Hydrochloride turn blue or darken upon light exposure?

Yes, it is notoriously photosensitive. Even brief exposure to light can cause a color change from white to blue or gray. It must be stored in amber glass or opaque containers at all times.

What is the best way to store Promethazine Hydrochloride in high-temperature warehouses?

In hot climates, we recommend storing it in climate-controlled areas or using insulated, refrigerated storage to prevent softening, caking, or accelerated degradation.

Is Promethazine Hydrochloride compatible with common antioxidant excipients?

Yes, when formulating solutions, the inclusion of antioxidants like ascorbic acid or sodium metabisulfite can help mitigate oxidation, and we can provide compatibility guidance.

How can I verify the integrity of a Promethazine Hydrochloride shipment upon arrival?

Inspect the color immediately upon receipt. If the powder shows any bluish tint, document it with photos and contact us for a quality investigation before use.