Phenergan: Expert Relief for Severe Nausea and Allergic Reactions
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Synonyms
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Phenergan (promethazine hydrochloride) is a phenothiazine-derivative antihistamine with significant sedative, antiemetic, and anticholinergic properties. It is a prescription medication widely utilized in clinical practice for its potent action on the central nervous system, particularly the chemoreceptor trigger zone (CTZ) and vomiting center. Its multifaceted pharmacological profile makes it a versatile agent for managing a range of conditions, from severe nausea and vomiting associated with motion sickness or postoperative recovery to symptomatic relief of allergic reactions. This expert overview details its appropriate use, mechanism, and essential safety considerations for healthcare professionals and informed patients.
Features
- Active Ingredient: Promethazine hydrochloride
- Pharmacological Class: Phenothiazine derivative, first-generation antihistamine (H1-receptor antagonist)
- Available Formulations: Oral tablets (12.5 mg, 25 mg, 50 mg), oral syrup, rectal suppositories, and injectable solution
- Mechanism of Action: Antagonizes histamine H1 receptors, depresses the CTZ, possesses anticholinergic and sedative effects
- Onset of Action: Oral: ~20 minutes; IV: ~3–5 minutes; duration of action is 4–6 hours (may extend to 12 hours)
- Metabolism: Hepatic, primarily via CYP2D6 and CYP2B6 isoenzymes; extensive first-pass metabolism
- Elimination Half-Life: Approximately 9–16 hours
Benefits
- Provides rapid and effective relief from severe nausea and vomiting, including that induced by anesthesia, chemotherapy, or motion sickness
- Offers potent antihistaminic action for alleviating symptoms of allergic conditions such as urticaria, angioedema, and allergic rhinitis
- Acts as a sedative adjunct pre- and postoperatively, or for temporary management of restlessness and agitation
- Serves as an antitussive agent for relieving nonproductive cough
- Augments the effects of analgesics for pain management, reducing required opioid dosage in some cases
- Available in multiple formulations allowing for flexible administration based on clinical need and patient tolerance
Common use
Phenergan is indicated for the management of nausea and vomiting of various etiologies, including postoperative nausea, motion sickness, and radiation sickness. It is also approved for the treatment of allergic conditions such as perennial and seasonal allergic rhinitis, allergic conjunctivitis, and mild uncomplicated allergic skin reactions. Additionally, it is used for sedation, as a preoperative adjunct, and for antiemetic and sedative effects in labor. Off-label uses may include migraine-associated nausea, vertigo, and as an adjunct in anaphylaxis management (though not first-line).
Dosage and direction
Dosage must be individualized based on indication, patient age, and clinical response.
Adults:
- Nausea/Vomiting: Oral/rectal: 12.5–25 mg every 4–6 hours as needed.
- Allergy: Oral/rectal: 12.5 mg before bed or 6.25–12.5 mg three times daily.
- Sedation: Oral/rectal: 25–50 mg at bedtime.
- Preoperative: 25–50 mg IM/IV 1 hour before procedure.
Pediatric (≥2 years):
Dosing based on weight; generally 0.25–1 mg/kg (max 25 mg) every 4–6 hours. Not recommended under age 2 due to risk of fatal respiratory depression.
Administer with food or milk to minimize GI upset. Avoid subcutaneous or intra-arterial injection due to risk of severe tissue injury. Do not administer IV at concentrations above 25 mg/mL or at rates exceeding 25 mg/min.
Precautions
Phenergan may cause marked drowsiness; patients should avoid driving or operating machinery until response is known. Use with caution in patients with cardiovascular disease, seizure disorders, narrow-angle glaucoma, prostatic hypertrophy, stenosing peptic ulcer, or bladder neck obstruction. May impair mental and physical abilities. Avoid alcohol and other CNS depressants. Elderly patients are at increased risk for sedation, confusion, and anticholinergic effects. Use cautiously in patients with respiratory conditions (e.g., asthma, COPD) due to potential suppression of cough reflex and thickening of secretions.
Contraindications
Hypersensitivity to promethazine or other phenothiazines. Comatose states, administration of large doses of CNS depressants. Neonates and children under 2 years of age due to risk of fatal respiratory depression. Not for use in subarachnoid administration. Avoid in patients with known sleep apnea or severe respiratory impairment. Contraindicated in patients with bone marrow suppression or blood dyscrasias.
Possible side effect
Common: Drowsiness, dizziness, blurred vision, dry mouth, nausea, vomiting.
Serious: Respiratory depression (especially in children), neuroleptic malignant syndrome, tardive dyskinesia, seizures, agranulocytosis, leukopenia, hypotension, tachycardia, jaundice, extrapyramidal symptoms (e.g., dystonia, akathisia). Tissue injury/necrosis with extravasation from IV administration. Severe skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis.
Drug interaction
- CNS depressants (e.g., opioids, benzodiazepines, alcohol): Enhanced sedative and respiratory depressant effects.
- Anticholinergics: Increased anticholinergic adverse effects.
- MAO inhibitors: May potentiate extrapyramidal effects; avoid concomitant use.
- Epinephrine: Phenergan may reverse epinephrine’s vasopressor effect; use norepinephrine instead.
- CYP2D6 inhibitors (e.g., fluoxetine, paroxetine): May increase promethazine levels.
- Hypotensive agents: Additive hypotensive effects.
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 catch up. Resume the regular dosing schedule.
Overdose
Overdose may cause severe CNS depression, respiratory depression, hypotension, agitation, hallucinations, convulsions, and coma. Cardiovascular collapse may occur. Treatment is supportive and symptomatic; there is no specific antidote. Maintain airway and assist ventilation if needed. Activated charcoal may be considered if administered soon after ingestion. Avoid stimulants (may induce seizures). Hemodialysis is not effective.
Storage
Store at controlled room temperature (20°–25°C or 68°–77°F). Protect from light. Keep oral formulations tightly closed. Do not freeze. Keep out of reach of children and pets. Discard unused or expired medication appropriately.
Disclaimer
This information is for educational purposes and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, changing, or stopping any medication. Do not disregard professional medical advice based on content herein.
Reviews
“Phenergan remains a valuable tool in our arsenal for managing postoperative nausea, especially in cases refractory to first-line antiemetics. Its sedative properties are an added benefit in anxious patients.” — Clinical Anesthesiologist
“Effective for severe allergic urticaria when second-generation antihistamines fail. Must monitor for sedation and use caution in elderly.” — Allergist-Immunologist
“Rapid-acting and reliable for chemotherapy-induced nausea, though we balance efficacy with risk of extrapyramidal symptoms in younger patients.” — Oncology Pharmacist
“Use with extreme caution in pediatric populations. Respiratory depression is a real and serious risk.” — Pediatric Intensivist