Promethazine is a versatile phenothiazine-derivative medication with potent antihistaminic, antiemetic, and sedative properties. It is widely utilized in clinical practice for the management of allergic conditions, nausea and vomiting, motion sickness, and as an adjunct to analgesia for its sedative effects. Its efficacy stems from its antagonistic action on histamine H1 receptors, along with effects on muscarinic and dopamine receptors, making it a multifunctional agent in both outpatient and inpatient settings. This product card provides a comprehensive overview for healthcare professionals to ensure informed, safe, and effective use.

Features

• Active Ingredient: Promethazine hydrochloride
• Pharmacological Class: First-generation antihistamine (H1-receptor antagonist), phenothiazine derivative
• Available Formulations: Oral tablets, syrup, suppositories, and injectable solutions
• Onset of Action: Oral: ~20 minutes; IV/IM: ~5–10 minutes
• Duration of Effect: 4–6 hours for allergic symptoms; up to 12 hours for sedation
• Metabolism: Hepatic, primarily via CYP2D6 and CYP2B6
• Elimination Half-life: Approximately 9–16 hours

Benefits

• Provides rapid and effective relief from symptoms of allergic reactions, including urticaria, rhinorrhea, and pruritus
• Effectively prevents and treats nausea and vomiting associated with motion sickness, surgery, or illness
• Offers sedative effects useful for preoperative preparation, adjunctive analgesia, or managing agitation
• Reduces vestibular disturbances in conditions like Ménière’s disease or vertigo
• Cost-effective and widely available in multiple formulations for flexible administration

Common use

Promethazine is commonly prescribed for the management of allergic conditions such as allergic rhinitis, conjunctivitis, and mild-to-moderate allergic skin reactions. It is also indicated for the prevention and treatment of nausea and vomiting, including postoperative nausea, motion sickness, and nausea associated with gastroenteritis or radiation therapy. Off-label, it is sometimes used for sedation, as an adjunct in pain management, and for treating vertigo.

Dosage and direction

Dosage must be individualized based on indication, patient age, and route of administration.

Adults:

• Allergies: 25 mg orally at bedtime; may increase to 12.5 mg before meals and at bedtime, or 25 mg at bedtime as needed.
• Nausea/Vomiting: 12.5–25 mg orally/IM/IV every 4–6 hours as needed.
• Motion Sickness: 25 mg orally 30–60 minutes before travel; repeat after 8–12 hours if needed.
• Sedation: 25–50 mg orally/IM/IV.

Pediatric Patients (≥2 years):

• Dosing based on weight and indication; generally 0.25–1 mg/kg/dose orally/IM/IV every 4–6 hours, not to exceed adult doses.

Note: Avoid intravenous push; administer IV slowly in a diluted solution to reduce risk of tissue injury. Do not administer subcutaneously or intra-arterially.

Precautions

• Use with caution in patients with respiratory conditions (e.g., asthma, COPD) due to potential suppression of cough reflex and respiratory depression.
• May cause drowsiness or impaired alertness; advise against driving or operating machinery.
• Risk of orthostatic hypotension; monitor in elderly or dehydrated patients.
• Use cautiously in patients with cardiovascular disease, glaucoma, prostatic hypertrophy, or seizure disorders.
• Avoid use in children under 2 years due to risk of respiratory depression and potential fatal respiratory side effects.
• May cause photosensitivity; advise sun protection.

Contraindications

• Hypersensitivity to promethazine or other phenothiazines.
• Comatose states or CNS depression due to barbiturates, alcohol, opioids, etc.
• Neonates and infants under 2 years of age.
• Suspected or established subcortical brain damage.
• Use in nursing mothers is not recommended due to secretion in breast milk and risk of adverse effects in the infant.

Possible side effect

Common side effects include:

• Drowsiness, sedation
• Dry mouth, blurred vision
• Dizziness, hypotension
• Tinnitus
• Fatigue

Less common but serious side effects:

• Extrapyramidal symptoms (e.g., dystonia, akathisia)
• Neuroleptic malignant syndrome (rare)
• Blood dyscrasias (e.g., agranulocytosis)
• Jaundice, hepatotoxicity
• Seizures
• Severe respiratory depression (especially in children and elderly)

Drug interaction

• CNS depressants (e.g., opioids, benzodiazepines, alcohol): Enhanced sedative effects.
• Anticholinergics: Additive effects such as dry mouth, urinary retention.
• MAO inhibitors: Risk of exaggerated anticholinergic and CNS depressant effects.
• Epinephrine: Avoid concomitant use due to potential reversal of pressor effect.
• Drugs metabolized by CYP2D6: Promethazine may inhibit metabolism of substrates like codeine, tramadol, antidepressants.

Missed dose

If a dose is missed, administer as soon as remembered unless it is nearly time for the next dose. Do not double the dose to make up for a missed one. Adjust schedule accordingly and resume regular dosing.

Overdose

Symptoms of overdose may include severe CNS depression (coma, respiratory depression), hypotension, agitation, hallucinations, convulsions, and cardiorespiratory arrest. Treatment is supportive and symptomatic: maintain airway, assist ventilation, administer IV fluids for hypotension. Avoid stimulants. Consider activated charcoal if ingestion was recent. There is no specific antidote.

Storage

Store at room temperature (15–30°C), away from light and moisture. Keep all formulations out of reach of children. Do not freeze liquid formulations. Discany unused or expired medication appropriately.

Disclaimer

This information is intended for healthcare professionals and is not a substitute for clinical judgment. Always verify dosing, indications, and contraindications with current prescribing guidelines and the product monograph. The prescriber is responsible for assessing individual patient factors and monitoring therapy.

Reviews

Promethazine has been extensively used since the 1950s and is generally regarded as effective for its indicated uses, particularly in managing allergies, nausea, and as a sedative. Clinical studies and decades of use support its efficacy, though caution is advised regarding its side effect profile, especially in vulnerable populations. It remains a valuable option in therapeutic arsenals when used appropriately under medical supervision.