Promethazine

Promethazine is used for relieving allergy symptoms, including hives or runny nose.

Product dosage: 25mg
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Synonyms Phenergan plain

Promethazine is a versatile phenothiazine-derived medication with potent antihistaminic, antiemetic, and sedative properties. Clinically utilized since the mid-20th century, it remains a trusted option for managing a range of conditions, from allergic responses and motion sickness to postoperative nausea and adjunctive analgesic sedation. Its multifunctional pharmacologic profile—acting primarily as an H1-receptor antagonist while also exhibiting anticholinergic and central dopamine D2 receptor blockade—makes it a valuable tool in both acute and preventive therapeutic contexts. Proper understanding of its indications, dosing protocols, and safety considerations is essential for optimizing patient outcomes.

Features

• Chemical class: Phenothiazine derivative
• Primary mechanism: Histamine H1-receptor antagonism
• Secondary actions: Anticholinergic and antidopaminergic effects
• Available forms: Oral tablets, syrup, suppositories, injectable solution
• Onset of action: ~20 minutes (IV/IM), ~30–60 minutes (oral)
• Duration of effect: 4–6 hours (may extend to 12 hours with sedative effects)

Benefits

• Provides rapid relief from acute allergic symptoms including urticaria, pruritus, and rhinorrhea
• Effectively prevents and treats nausea and vomiting associated with motion, surgery, or illness
• Offers sedative effects useful for preoperative preparation or adjunctive use in analgesia
• Reduces anxiety and promotes calm in selected clinical scenarios
• Cost-effective compared to many newer antiemetic or sedative alternatives
• Available in multiple formulations allowing flexible administration routes

Common use

Promethazine is commonly prescribed for the management of allergic conditions such as allergic rhinitis, conjunctivitis, and mild allergic skin reactions. It is also widely used as an antiemetic in cases of motion sickness, postoperative nausea, and nausea associated with gastroenteritis or radiation therapy. In clinical settings, it is sometimes employed for its sedative properties to alleviate anxiety or as an adjunct to analgesics for enhanced effect. Off-label uses may include management of migraine-associated nausea and as a short-term sleep aid, though these are not primary indications.

Dosage and direction

Dosage varies by indication, age, and route of administration. For adults with allergies or motion sickness, the typical oral dose is 25 mg taken at bedtime or 12.5 mg before meals and at bedtime. For nausea/vomiting, doses of 12.5–25 mg every 4–6 hours are common. Injectable forms are reserved for severe nausea or postoperative use. Pediatric dosing is weight-based and must be carefully calculated. Administration with food or milk may reduce gastrointestinal upset. Do not crush or break extended-release formulations. Always follow specific prescribing instructions.

Precautions

Use with caution in patients with respiratory conditions (e.g., asthma, COPD), as promethazine may suppress cough reflex and thicken secretions. Avoid in patients with narrow-angle glaucoma, prostatic hypertrophy, or bladder neck obstruction due to anticholinergic effects. May impair mental or physical abilities; caution against driving or operating machinery. Elderly patients are more susceptible to sedative and hypotensive effects. Use during pregnancy only if clearly needed; not recommended during breastfeeding. Periodic liver and blood monitoring may be advised during prolonged use.

Contraindications

Promethazine is contraindicated in individuals with known hypersensitivity to phenothiazines or any component of the formulation. It should not be used in comatose patients, or in those with significant CNS depression. Contraindicated in children under 2 years of age due to risk of fatal respiratory depression. Avoid use in patients with severe hepatic impairment, subcortical brain damage, or bone marrow suppression. Concomitant use with MAO inhibitors is contraindicated.

Possible side effect

Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and constipation. Less frequently, patients may experience hypotension, tachycardia, extrapyramidal symptoms (e.g., dystonia, akathisia), or photosensitivity. Rare but serious adverse effects include neuroleptic malignant syndrome, agranulocytosis, and seizures. Respiratory depression is a risk, particularly in pediatric or debilitated patients. Allergic reactions, though uncommon, may include rash or anaphylaxis.

Drug interaction

Promethazine may potentiate CNS depression when used with alcohol, barbiturates, opioids, or other sedatives. Concurrent use with anticholinergics may increase side effects like dry mouth or urinary retention. May counteract the effects of dopamine agonists. Caution with hypotensive agents, as additive blood pressure-lowering effects may occur. Avoid with MAOIs due to risk of hyperthermia and severe hypertension. May alter absorption of other orally administered drugs.

Missed dose

If a dose is missed, take it as soon as remembered unless it is nearly time for the next dose. Do not double the dose to catch up. Resume the regular dosing schedule. If uncertain, consult a healthcare provider for guidance. Consistent dosing is important for therapeutic effect, particularly when used for prevention (e.g., motion sickness).

Overdose

Overdose may manifest as severe CNS depression (ranging from drowsiness to coma), hypotension, respiratory depression, agitation, hallucinations, or convulsions. Anticholinergic symptoms such as dry mouth, fixed dilated pupils, and flushed skin may occur. Cardiovascular collapse is possible in severe cases. Treatment is supportive and may include airway management, activated charcoal (if recent ingestion), and IV fluids for hypotension. There is no specific antidote. Contact poison control or seek emergency medical attention immediately.

Storage

Store at room temperature (15–30°C), away from light, moisture, and heat. Keep oral solutions and tablets in their original container, tightly closed. Do not freeze liquid formulations. Keep out of reach of children and pets. Do not use beyond the expiration date. Properly discard any unused or expired medication according to local guidelines.

Disclaimer

This information is intended for educational purposes and does not constitute medical advice. Always consult a qualified healthcare professional before starting, changing, or stopping any medication. Individual response to promethazine may vary. Not all uses, precautions, or interactions may be listed. The prescriber should be informed of full medical history and concurrent medications.

Reviews

Clinical studies and decades of use support the efficacy of promethazine for allergic and antiemetic indications. Many clinicians appreciate its rapid onset and cost-effectiveness. However, sedation and potential for extrapyramidal symptoms are frequently noted drawbacks. Parental and geriatric populations require particular caution. Overall, when used appropriately and under medical supervision, promethazine remains a useful agent in specific clinical scenarios.