Best Quality99% Promethazine Hydrochloride CAS:58-33-3 for Antiemetic & antidizziness

1. Chlorpheniramine Maleate
2. Diphenhydramine Hydrochloride
3. Hydroxyzine Hydrochloride

Promethazine hydrochloride, a first-generation phenothiazine derivative with the CAS 58-33-3, has been a clinical staple for over seventy years, widely recognized for its multipurpose therapeutic values. Structurally, this racemic compound differs from antipsychotic phenothiazines due to its branched, non-aromatic side chain, which reduces its dopamine D₂-receptor antagonism compared to chlorpromazine, while maintaining high affinity for histamine H₁ receptors. This structural distinction enables promethazine to retain significant therapeutic versatility, including potent antihistaminic, moderate anticholinergic, sedative, anti-emetic, and local anesthetic properties.

Chemical and Physical Properties

Promethazine hydrochloride manifests as a white to faint-yellow, almost odorless crystalline powder, possessing a bitter taste. It is freely soluble in water and alcohol, soluble in chloroform, and almost insoluble in ether, acetone.It has a molecular formula of C₁₇H₂₀N₂S·HCl and a molecular weight of 320.88. The compound melts at 230–232 °C with decomposition, and its solid form is susceptible to slow oxidation when exposed to air, turning the surface blue over time.

Pharmacokinetics

This compound exhibits excellent oral bioavailability, with measurable plasma levels manifesting within 15–20 minutes post-administration. The clinical effects last around 4–6 hours, though sedation may endure for 12 hours or more. Metabolized predominantly in the liver to promethazine sulfoxide and N-demethylpromethazine, the drug is eliminated via urine, with an elimination half-life ranging between 9–16 hours. Conditions like hepatic impairment or the use of CYP2D6 inhibitors may prolong promethazine exposure.

Therapeutic Applications

Promethazine hydrochloride's diverse receptor profile underpins its varied therapeutic indications. For allergic disorders, it effectively alleviates rhinorrhoea, pruritus, and urticaria by competitively blocking peripheral H₁ receptors. Its efficacy extends to central nervous system applications, where its central H₁ blockade, combined with muscarinic and 5-HT antagonism, depresses critical regions such as the medial forebrain bundle and chemoreceptor trigger zone. This mechanism supports its use in managing motion sickness, post-operative nausea, drug-induced emesis, and morning sickness.

In clinical practice, the drug is exploited for pre-operative anxiolysis, obstetric sedation, and as a facilitator in opioid analgesia, allowing for lower narcotic doses. Additionally, promethazine's type-I anti-arrhythmic activity, through reversible Na⁺-channel blockade, is beneficial for infiltrative anesthesia applications where lidocaine is contraindicated.

Safety Profile and Adverse Effects

Promethazine hydrochloride's extensive receptor occupancy is reflected in its adverse effect profile, predominantly featuring drowsiness, dizziness, psychomotor impairment, and anticholinergic effects such as dry mouth, blurred vision, constipation, and urinary retention. Serious risks include orthostatic hypotension, QT prolongation, and less frequently, blood dyscrasias and hypersensitivity dermatitis. Overuse, renal or hepatic impairment, and vulnerabilities in extremes of age can provoke more severe reactions like confusion, hallucinations, extrapyramidal effects, and respiratory depression. Crucially, it carries a boxed warning against use in children under two years due to the risk of fatal respiratory arrest.

Drug Interactions

Promethazine interacts with numerous substances, potentiating CNS depression with alcohol, barbiturates, benzodiazepines, and opioids. Simultaneous use with anticholinergic agents can heighten the risk of severe side effects.

Special Populations

Promethazine hydrochloride is classified as Pregnancy Category C; hence, it should be used conservatively, only when benefits justify potential fetal risks. It is excreted into breast milk, though its short-term use is generally deemed compatible with breastfeeding.

Conclusion

Despite the advent of newer antihistamines and antiemetics, promethazine hydrochloride remains a cornerstone in managing conditions requiring rapid, effective H₁ blockade and sedation. However, prudence is required when prescribing, particularly in vulnerable populations, to balance its therapeutic benefits against the risk of significant adverse effects.