Promethazine Hydrochloride Injection

What is Promethazine Hydrochloride Injection?
Promethazine Hydrochloride Injection is a sterile solution of a potent first-generation antihistamine belonging to the phenothiazine group. Unlike newer antihistamines, Promethazine crosses the blood-brain barrier easily, providing significant sedative, antiemetic (anti-nausea), and anticholinergic effects. In clinical settings, it is a versatile "workhorse" medication used for everything from emergency allergic stabilization to providing pre-operative "twilight" sedation.
Uses of Promethazine Hydrochloride Injection
Allergic Reactions: Management of allergic rhinitis, conjunctivitis, and uncomplicated skin reactions (urticaria). It is also used as an adjunct to epinephrine in anaphylaxis.
Nausea & Vomiting: Prevention and control of nausea and vomiting associated with surgery, anesthesia, or motion sickness.
Sedation: Providing preoperative, postoperative, or obstetric sedation to relieve apprehension and produce light sleep.
Potentiation of Analgesics: Used as an adjunct to opioid painkillers (like Morphine) to enhance their sedative effect and reduce associated nausea.
Motion Sickness: Rapid relief for severe symptoms of motion sickness when oral medication cannot be retained.
How Does Promethazine Hydrochloride Injection Work?
Promethazine works through multiple pathways in the body. Primarily, it acts as an H1-receptor antagonist, blocking the effects of histamine on smooth muscle and blood vessels. Its anti-nausea effect comes from its ability to block dopaminergic receptors in the chemoreceptor trigger zone (CTZ) of the medulla. Additionally, its high affinity for muscarinic and alpha-adrenergic receptors contributes to its sedative and drying (anticholinergic) properties.
FAQs on Promethazine Hydrochloride Injection
1. Can Promethazine be given via any intravenous (IV) site? Extreme caution is required with IV administration. Promethazine is highly alkaline and can be caustic to the veins. It should be administered through a large, high-flow vein, preferably after being diluted. Deep intramuscular (IM) injection is often the preferred and safer route of administration.
2. Why is there a "Black Box Warning" for children? Promethazine is strictly contraindicated in children under the age of 2 years due to the risk of severe, potentially fatal respiratory depression. In children older than 2, the lowest effective dose should always be used.
3. Does it cause significant drowsiness? Yes. Intense drowsiness is the most common side effect. While this is beneficial when used for sedation, patients must be monitored for excessive CNS depression, especially if Promethazine is being used alongside other sedatives or opioids.
Therapeutic Category
Antihistamine / Antiemetic / Sedative
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