Phenergan (promethazine hydrochloride) is a versatile prescription medication belonging to the phenothiazine class of drugs. It is primarily indicated for the management of nausea, vomiting, and allergic conditions. With its potent antihistaminic, antiemetic, and sedative properties, it is a trusted therapeutic option in both hospital and outpatient settings. Its efficacy is supported by decades of clinical use and a well-understood pharmacological profile, making it a cornerstone in symptomatic treatment protocols.

Features

• Active Ingredient: Promethazine hydrochloride
• Available Formulations: Tablets, syrup, suppositories, and injectable solution
• Mechanism of Action: Antagonizes histamine H1 receptors, and possesses significant anticholinergic and central sedative effects
• Onset of Action: Oral administration typically shows effects within 20 minutes, with duration lasting 4–6 hours (may extend to 12 hours)
• Dosage Strengths: Tablets: 12.5 mg, 25 mg; Syrup: 6.25 mg/5 mL; Suppositories: 12.5 mg, 25 mg; Injection: 25 mg/mL, 50 mg/mL

Benefits

• Provides rapid and effective relief from nausea and vomiting associated with motion sickness, surgery, or illness
• Effectively alleviates symptoms of allergic reactions, including rhinitis, urticaria, and conjunctivitis
• Offers sedative effects beneficial for preoperative sedation, adjunctive analgesia, and managing anxiety-related insomnia
• Helps reduce coughing through its mild antitussive properties, often incorporated into cough preparations
• Supports postoperative recovery by minimizing nausea and promoting rest
• Available in multiple formulations to suit varying patient needs and clinical scenarios

Common use

Phenergan is commonly prescribed for the prevention and treatment of nausea and vomiting, including that related to motion sickness, postoperative recovery, and gastroenteritis. It is also widely used for managing allergic conditions such as hay fever, allergic rhinitis, and skin reactions like hives. In clinical practice, it serves as a sedative for procedures, an adjunct to analgesics for pain management, and a component in some cough and cold preparations due to its antitussive effects.

Dosage and direction

Dosage must be individualized based on the patient’s age, condition, and response. Administer with caution due to sedation potential.

• Adults (Nausea/Vomiting): 12.5–25 mg orally, rectally, or IM every 4–6 hours as needed.
• Adults (Allergy): 12.5 mg orally before bedtime or 25 mg at bedtime; may also use 6.25–12.5 mg three times daily.
• Adults (Sedation): 25–50 mg IM or orally preoperatively or at bedtime.
• Pediatric (≥2 years): Dosing based on weight and indication; generally 0.25–1 mg/kg (max 25 mg) every 4–6 hours. Not recommended under age 2 due to risk of respiratory depression.
• Elderly: Use lower doses; increased susceptibility to adverse effects.

Always take as directed by a healthcare provider. Oral forms may be taken with food or milk to reduce GI upset. Avoid alcohol and CNS depressants.

Precautions

• May cause drowsiness; avoid driving or operating machinery until response is known.
• Use with caution in patients with respiratory impairment, asthma, or sleep apnea.
• Risk of severe tissue injury including gangrene if administered intra-arterially or subcutaneously; IV administration should be avoided or used with extreme caution.
• May lower seizure threshold; use cautiously in those with seizure disorders.
• Can cause anticholinergic effects (e.g., dry mouth, blurred vision, urinary retention); use care in patients with glaucoma, prostate hypertrophy.
• Elderly patients are at increased risk for falls, confusion, and anticholinergic effects.

Contraindications

• Known hypersensitivity to promethazine or any component of the formulation.
• Children under 2 years of age due to potential for fatal respiratory depression.
• Comatose states or significant CNS depression.
• Concomitant use with MAO inhibitors (risk of hyperthermia, seizures).
• Intra-arterial or subcutaneous injection.

Possible side effect

Common side effects may include:

• Drowsiness, sedation
• Dizziness
• Blurred vision
• Dry mouth
• Nausea
• Constipation

Less common but serious side effects:

• Respiratory depression
• Neuroleptic malignant syndrome (NMS)
• Severe tissue injury (if improperly injected)
• Seizures
• Blood dyscrasias (e.g., leukopenia, agranulocytosis)
• Jaundice
• Extrapyramidal symptoms (e.g., dystonia, akathisia)

Drug interaction

• CNS Depressants: Enhanced sedation with alcohol, opioids, benzodiazepines, barbiturates.
• MAO Inhibitors: Risk of hyperpyrexia, hypertension, seizures; avoid concomitant use.
• Anticholinergics: Additive effects (e.g., with atropine, tricyclic antidepressants).
• Epinephrine: May reverse epinephrine’s vasopressor effect; use norepinephrine instead if needed.
• Drugs Prolonging QT Interval: Possible additive effect; use with caution.

Missed dose

If a dose is missed, take it as soon as remembered unless it is almost time for the next dose. Do not double the dose to catch up. Resume the regular dosing schedule. Consult a healthcare provider if unsure.

Overdose

Overdose may lead to severe CNS depression, respiratory depression, hypotension, seizures, coma, or anticholinergic crisis (e.g., hyperthermia, flushed skin). Treatment is supportive and symptomatic; there is no specific antidote. Maintain airway, assist ventilation if needed. Activated charcoal may be considered if ingestion recent. Avoid stimulants. Seek immediate medical attention.

Storage

Store at room temperature (20–25°C/68–77°F), away from light and moisture. Keep all forms out of reach of children and pets. Do not freeze liquid formulations. Discard unused medication appropriately; do not flush or pour down drain unless instructed.

Disclaimer

This information is for educational purposes only and 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.

Reviews

“Phenergan has been invaluable in our postoperative care protocols. Its antiemetic efficacy is reliable, though sedation requires careful patient monitoring.” – Dr. A. Lee, Anesthesiologist

“As an allergist, I find Phenergan useful for acute allergic presentations, especially when sedation is also desired. However, I caution against use in very young children and advise lower doses in the elderly.” – Dr. R. Sharma, Allergist-Immunologist

“Effective for nausea, but the drowsiness can be significant. Patients should be counseled not to drive or make important decisions while on this medication.” – Clinical Pharmacist Review