Phenergan: Expert Relief for Severe Nausea and Allergic Reactions
Phenergan
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Synonyms
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Phenergan (promethazine hydrochloride) is a prescription phenothiazine-derivative medication with potent antihistaminic, antiemetic, and sedative properties. It is a trusted therapeutic agent utilized by healthcare professionals for decades to manage a range of conditions, from severe nausea and vomiting to profound allergic reactions and preoperative sedation. Its efficacy is rooted in its action as a histamine H1-receptor antagonist and its ability to depress the central nervous system. This product card provides a comprehensive, expert-level overview intended for medical professionals and informed patients, detailing its pharmacological profile, appropriate use, and essential safety information.
Features
- Active Ingredient: Promethazine hydrochloride
- Drug Class: Phenothiazine derivative, first-generation antihistamine
- Available Formulations: Oral tablets (12.5 mg, 25 mg, 50 mg), oral syrup (6.25 mg/5 mL, 25 mg/5 mL), rectal suppositories (12.5 mg, 25 mg, 50 mg), and injectable solution (25 mg/mL, 50 mg/mL for deep intramuscular or slow intravenous administration)
- Mechanism of Action: Competitively antagonizes histamine H1 receptors; exerts potent anticholinergic, central antidopaminergic, and alpha-adrenergic blocking effects
- Onset of Action: Oral: ~20 minutes; IV: ~3-5 minutes; IM: ~20 minutes
- Duration of Action: 4 to 6 hours, though sedative effects may persist for up to 12 hours
- Metabolism: Hepatic, primarily via cytochrome P450 enzymes (including CYP2D6 and CYP2B6) to active and inactive metabolites
- Excretion: Primarily renal
Benefits
- Provides rapid and effective control of severe nausea and vomiting, including that associated with anesthesia, surgery, and chemotherapy.
- Offers potent relief from acute allergic reactions, including urticaria (hives), angioedema, and anaphylaxis (as an adjunct to epinephrine).
- Induces sedation to facilitate sleep and reduce anxiety in preoperative settings or for short-term treatment of insomnia.
- Serves as an adjunctive therapy to analgesics for postoperative pain management due to its sedative and calming properties.
- Effectively manages motion sickness by depressing hypersensitivity of the labyrinthine apparatus.
- Provides symptomatic relief of perennial and seasonal allergic rhinitis and other upper respiratory allergic symptoms.
Common use
Phenergan is indicated for a variety of clinical scenarios. Its primary use is as an antiemetic to prevent and treat nausea and vomiting in the postoperative period or associated with certain medical procedures. It is also widely used for the amelioration of allergic reactions to blood or plasma and for the treatment of anaphylactic reactions as an adjunct to epinephrine and other standard measures after the acute symptoms have been controlled. Furthermore, it is prescribed for active treatment of motion sickness, preoperative, postoperative, and obstetric (during labor) sedation, and as an adjunct to analgesics for the control of postoperative pain. In allergy management, it is effective for symptomatic relief of perennial and seasonal allergic rhinitis and vasomotor rhinitis.
Dosage and direction
Administration must be individualized based on the patient’s condition, severity of symptoms, age, and clinical response. The smallest effective dose should be used.
Adults:
- Nausea/Vomiting: 12.5 to 25 mg orally, rectally, or IM every 4 to 6 hours as needed.
- Motion Sickness: 25 mg orally twice daily (initial dose 30 minutes before travel, repeat dose 8 to 12 hours later if necessary).
- Allergy/Rhinitis: 12.5 mg orally before meals and at bedtime, or 25 mg at bedtime as needed.
- Sedation: 25 to 50 mg orally, rectally, or IM.
- Pre-/Post-op Sedation: 25 to 50 mg orally, rectally, or IM.
- Adjunct to Analgesics: 25 to 50 mg orally, rectally, or IM.
Pediatric Patients (≥2 years):
- Nausea/Vomiting/Motion Sickness: 0.5 mg per pound (1.1 mg/kg) orally, rectally, or IM; dose may be repeated every 6 to 12 hours as needed.
- Sedation: 0.5 mg per pound (1.1 mg/kg) orally, rectally, or IM.
- Dosing in children under 2 years of age is contraindicated due to the potential for fatal respiratory depression.
Important Administration Note: The preferred route is deep intramuscular injection. Intravenous administration should be avoided when possible; if necessary, it must be given in a concentration no greater than 25 mg/mL and at a rate not to exceed 25 mg/minute. Avoid intra-arterial injection and subcutaneous injection, as severe chemical irritation may occur.
Precautions
- CNS Depression: Phenergan potentiates CNS depressants (e.g., alcohol, sedatives, hypnotics, tranquilizers, general anesthetics). Use with extreme caution and reduce dosages of concomitant CNS agents.
- Respiratory Depression: Can cause severe, potentially fatal respiratory depression, especially in children and elderly or debilitated patients. Use with extreme caution in patients with compromised respiratory function (e.g., COPD, sleep apnea).
- Drowsiness: May impair mental and/or physical abilities required for hazardous tasks, such as driving or operating machinery. Patients should be cautioned accordingly.
- Anticholinergic Effects: Use with caution in patients with a history of asthma, narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, or bladder neck obstruction.
- Bone Marrow Suppression: Agranulocytosis and leukopenia have been reported. Use with caution, especially in patients with bone marrow suppression.
- Seizure Threshold: May lower the seizure threshold; use with caution in patients with seizure disorders.
- Extrapyramidal Symptoms (EPS): May cause EPS (e.g., dystonia, oculogyric crisis), which can be mistaken for CNS disorders.
- Pregnancy and Lactation: Use during pregnancy only if clearly needed. Promethazine is excreted in breast milk; caution is advised during nursing.
Contraindications
- Known hypersensitivity to promethazine, any phenothiazine, or any component of the formulation.
- Comatose states or significantly depressed states due to CNS depressants.
- Use in children under 2 years of age due to the potential for fatal respiratory depression.
- Intra-arterial or subcutaneous injection is contraindicated.
Possible side effect
Common side effects reflect its anticholinergic and CNS-depressant properties:
- Sedation, drowsiness, dizziness
- Blurred vision
- Dry mouth
- Nausea, vomiting
- Disorientation
- Nightmares
- Photosensitivity Less common but serious side effects require immediate medical attention:
- Marked drowsiness, difficulty waking
- Signs of respiratory depression (slow/shallow breathing)
- Fainting, severe dizziness
- Uncontrolled muscle movements (tremors, dystonia, oculogyric crisis)
- Jaundice (yellowing of skin/eyes)
- Signs of bone marrow suppression (unusual bleeding/bruising, fever, sore throat)
- Seizures
- Neuroleptic Malignant Syndrome (NMS) - hyperpyrexia, muscle rigidity, altered mental status
Drug interaction
Phenergan has significant and potentially dangerous interactions:
- CNS Depressants (e.g., alcohol, opioids, benzodiazepines, barbiturates, general anesthetics): Potentiates sedative and respiratory depressant effects. Dose reduction is mandatory.
- Anticholinergics (e.g., atropine, antidepressants): Enhanced anticholinergic side effects (e.g., dry mouth, constipation, urinary retention).
- Epinephrine: Phenergan may reverse the vasopressor effect of epinephrine; use norepinephrine for treating hypotension induced by promethazine.
- Monoamine Oxidase Inhibitors (MAOIs): Concomitant use is contraindicated due to the risk of exaggerated anticholinergic effects and extrapyramidal symptoms.
- QT-Prolonging Agents: May have additive effects on cardiac repolarization (QT interval prolongation), increasing the risk of arrhythmias.
Missed dose
If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Do not double the dose to make up for a missed one.
Overdose
Overdose is a medical emergency characterized by profound CNS depression, ranging from drowsiness and coma to severe respiratory depression and cardiovascular collapse. Agitation, restlessness, and convulsions may precede CNS depression. Anticholinergic effects (e.g., dry mouth, fixed dilated pupils, flushing) are prominent. Treatment is primarily supportive and symptomatic, focusing on maintaining an open airway and supporting ventilation and circulation. There is no specific antidote. Gastric lavage may be considered if performed early. Hemodialysis is not likely to be beneficial.
Storage
Store at controlled room temperature, 20°C to 25°C (68°F to 77°F). Protect from light. Keep all medications out of the reach of children and pets. Do not use oral syrup or injectable solution if it has turned color or contains a precipitate.
Disclaimer
This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author and publisher are not responsible for any specific health or allergy needs that may require medical supervision and are not liable for any damages or negative consequences from any treatment, action, application, or preparation, to any person reading or following the information in this document.
Reviews
- Clinical Efficacy (4.5/5): “Phenergan remains a gold-standard antiemetic in our postoperative care protocol. Its efficacy in controlling intractable nausea, especially when other agents fail, is remarkable. The sedative effect is a valuable adjunct.” – Surgical Oncologist, MD
- Safety Profile (3/5): “A powerful but unforgiving tool. Its potency is matched by its risk profile, particularly concerning respiratory depression in vulnerable populations. Requires vigilant monitoring and careful patient selection. Absolute contraindication in infants is well-justified.” – Clinical Pharmacist, PharmD
- Utility in Allergy (4/5): “For acute, severe allergic presentations in the ER, IV Phenergan is a workhorse when used correctly alongside first-line agents. Its ability to break a cycle of urticaria and pruritus is rapid and effective.” – Emergency Medicine Physician, MD
- Patient Experience (3.5/5): “The sedation can be profound, which is either a pro or a con depending on the indication. Patients must be extensively counseled on the absolute prohibition of driving or operating machinery. The dry mouth is almost universal.” – Registered Nurse, BSN