Phenergan: Expert Relief for Severe Nausea and Allergic Reactions
Phenergan
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Synonyms
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Phenergan (promethazine hydrochloride) is a phenothiazine-derivative antihistamine with well-established efficacy in managing severe nausea, vomiting, and allergic conditions. As a prescription medication with potent central and peripheral actions, it operates primarily by antagonizing histamine H1 receptors, though it also exhibits significant anticholinergic, sedative, and antiemetic properties. Its use is reserved for situations where first-line treatments are insufficient, given its potential for serious side effects, including respiratory depression in children and heightened sedation. This expert-oriented guide details its pharmacological profile, appropriate clinical applications, and essential safety considerations for healthcare providers and informed patients.
Features
- Active ingredient: Promethazine hydrochloride
- Available formulations: Oral tablets (12.5 mg, 25 mg, 50 mg), syrup, suppositories, injectable solution
- Mechanism: Potent H1-histamine receptor antagonist with additional anticholinergic and antidopaminergic effects
- Onset of action: Oral—~20 minutes; IV—~3–5 minutes; duration up to 12 hours
- Pregnancy category: Not formally assigned; use only if potential benefit justifies potential risk
- Half-life: Approximately 9–16 hours
Benefits
- Provides rapid and effective relief from severe nausea and vomiting, including postoperative and motion-related nausea
- Controls symptoms of allergic reactions such as urticaria, angioedema, and allergic rhinitis through potent antihistaminic action
- Offers adjunctive sedation and anxiolysis in perioperative and acute clinical settings
- Reduces severity and duration of vertigo and labyrinthine disorders
- Serves as an adjunct to analgesics for postoperative pain management due to its sedative and antiemetic properties
Common use
Phenergan is indicated for the management of severe nausea and vomiting, particularly in postoperative settings or when associated with motion sickness. It is also used for symptomatic relief of allergic conditions, including perennial and seasonal allergic rhinitis, and as a sedative for procedural anxiety or preoperatively. Off-label uses may include migraine-associated nausea, vertigo, and as an adjunct in anaphylaxis management. Its use should be reserved for cases where less sedating alternatives have failed or are contraindicated.
Dosage and direction
Dosage must be individualized based on indication, patient age, and clinical context. For adults: nausea/vomiting—12.5–25 mg every 4–6 hours as needed; allergy—12.5 mg before bed or 6.25–12.5 mg three times daily; sedation—25–50 mg preoperatively or at bedtime. For children ≥2 years: 0.25–1 mg/kg/dose every 4–6 hours, not to exceed 25 mg for initial dose. Administer orally with food or water to minimize gastrointestinal irritation. Avoid intravenous push; administer deep intramuscularly or by slow IV infusion to reduce risk of tissue injury or severe chemical irritation. Do not administer subcutaneously or intra-arterially.
Precautions
Phenergan may cause significant drowsiness; patients should avoid driving or operating machinery until response is known. Caution is advised in elderly patients due to increased risk of confusion, dizziness, and hypotension. Use with care in patients with cardiovascular disease, narrow-angle glaucoma, prostate hypertrophy, or seizure disorders. Avoid use in patients with bone marrow suppression or hepatic impairment. Phenergan can suppress cough reflex; avoid use in patients with asthma, pneumonia, or other respiratory conditions. Not recommended for children under 2 years due to risk of fatal respiratory depression.
Contraindications
Phenergan is contraindicated in patients with known hypersensitivity to promethazine or other phenothiazines. It is contraindicated in comatose states, and in children under 2 years of age. Do not use in patients with suspected Reye’s syndrome or other hepatic encephalopathies. Avoid use in patients with severe CNS depression, bone marrow suppression, or those taking monoamine oxidase inhibitors (MAOIs). Contraindicated in patients with a history of sleep apnea or severe respiratory compromise.
Possible side effect
Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and hypotension. Less frequently, patients may experience confusion, extrapyramidal symptoms (e.g., dystonia, akathisia), or photosensitivity. Rare but serious adverse effects include neuroleptic malignant syndrome, agranulocytosis, seizures, and respiratory depression. Tissue necrosis and gangrene may occur with perivascular extravasation or intra-arterial injection. Paradoxical reactions (e.g., excitation, nightmares) may occur, particularly in children and elderly patients.
Drug interaction
Phenergan may potentiate CNS depression when used with alcohol, barbiturates, opioids, anxiolytics, or other sedatives. Concurrent use with MAOIs may increase risk of extrapyramidal symptoms and hyperthermia. Anticholinergic effects may be enhanced when used with tricyclic antidepressants or other anticholinergic drugs. Phenergan may counteract the effects of dopamine agonists (e.g., levodopa) and may increase the risk of arrhythmias with drugs that prolong QT interval. Use cautiously with antihypertensives due to additive hypotensive effects.
Missed dose
If a dose is missed, administer as soon as remembered unless it is nearly time for the next scheduled dose. Do not double the dose to make up for a missed one. For as-needed use, this guidance may not apply; resume normal dosing schedule with the next required dose.
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 symptomatic; there is no specific antidote. Maintain airway and provide assisted ventilation if needed. Activated charcoal may be considered if ingestion was recent. Avoid stimulants which may precipitate seizures.
Storage
Store at controlled room temperature (20–25°C or 68–77°F). Protect from light and moisture. Keep oral formulations tightly closed. Do not freeze. Keep out of reach of children and pets. Discard unused or expired medication according to local guidelines; do not flush unless instructed.
Disclaimer
This information is intended 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. Individual patient responses may vary.
Reviews
Phenergan is regarded by clinicians as a highly effective agent for refractory nausea and perioperative sedation, though its use is tempered by concerns regarding sedation and respiratory risks, particularly in pediatric and geriatric populations. Clinical studies support its efficacy in controlling emesis and allergic symptoms, but caution is emphasized in patient selection and monitoring. It remains a valuable option in specific clinical scenarios where benefits outweigh risks.