What is the recommended dose of promethazine (Phenergan) for pediatric patients?

Promethazine Dosing in Pediatric Patients

Critical Age Restriction

Promethazine is contraindicated in children under 2 years of age due to risk of fatal respiratory depression. 1

Standard Pediatric Dosing by Indication

Allergy

• Children ≥2 years: 6.25 to 12.5 mg orally three times daily, or 12.5 mg at bedtime 1
• After initiation, adjust dosage to the smallest amount adequate to relieve symptoms 1
• Single 25 mg doses at bedtime or 6.25 to 12.5 mg three times daily will usually suffice 1

Motion Sickness

• Children ≥2 years: 12.5 to 25 mg orally twice daily 1
• Initial dose should be taken one-half to one hour before anticipated travel and repeated 8 to 12 hours later if necessary 1

Nausea and Vomiting

• Weight-based dosing: 0.5 mg per pound of body weight (approximately 1.1 mg/kg) 1
• Alternative fixed dosing: 12.5 to 25 mg every 4 to 6 hours as necessary 1
• Adjust dose to the age and weight of the patient and severity of the condition 1
• Important caveat: Antiemetics should not be used in vomiting of unknown etiology in children and adolescents 1

Sedation

• Nighttime sedation: 12.5 to 25 mg orally or by rectal suppository at bedtime 1
• Preoperative medication: 0.5 mg per pound of body weight (approximately 1.1 mg/kg) in combination with appropriately reduced doses of narcotic or barbiturate and atropine-like drug 1
• Postoperative sedation: 12.5 to 25 mg 1

Formulation Considerations

• Available as tablets (12.5,25,50 mg), syrup (6.25 mg/5 mL), and rectal suppositories 2
• Oral syrup is preferred over rectal suppositories when possible due to more consistent absorption 2

Critical Safety Warnings

Respiratory Depression Risk

• Promethazine can cause significant respiratory depression, particularly when combined with other sedatives 3, 4
• In one study, 4 of 95 patients (4.2%) developed respiratory depression, with one requiring naloxone and another experiencing respiratory arrest 4
• Patients with acute or underlying neurologic abnormalities are at significantly increased risk for complications 5

Other Serious Adverse Effects

• High sedation rate: 60-73%, substantially higher than second-generation antihistamines 2
• Can cause agitation, hallucinations, seizures, and dystonic reactions 3
• Possible association with apparent life-threatening events or sudden infant death syndrome 3
• Has substantial anticholinergic effects 2

Management of Dystonic Reactions

• If acute dystonic reactions occur, administer diphenhydramine 1-2 mg/kg or 25-50 mg parenterally 2

Common Pitfalls to Avoid

1. Never use in children <2 years old - this is an absolute contraindication with black box warning 1
2. Avoid in patients with head injuries or neurologic abnormalities - significantly increased complication risk 5
3. Do not combine with other sedatives without extreme caution - additive respiratory depression risk 4
4. Avoid using for vomiting of unknown etiology - may mask serious underlying conditions 1
5. Monitor frequently when used parenterally - respiratory depression can occur within 30 minutes even at recommended doses 4