What is the recommended pediatric dose of Phenargen (promethazine)?

Phenargen (Promethazine) Pediatric Dosing

Promethazine is contraindicated in children under 2 years of age due to risk of fatal respiratory depression, and for children 2 years and older, the dose is 0.5 mg per pound (approximately 1 mg/kg) of body weight, adjusted to the smallest amount adequate to relieve symptoms. 1

Critical Age Restriction

• Promethazine is absolutely contraindicated for children under 2 years of age due to severe respiratory depression risk, including potential sudden infant death syndrome and apparent life-threatening events 1, 2
• This is an FDA Black Box Warning that must be strictly observed 1

Standard Pediatric Dosing (Children ≥2 Years)

For Allergies

• Initial dose: 6.25 to 12.5 mg three times daily 1
• Alternative regimen: 12.5 mg before meals and at bedtime 1
• Adjust to the smallest amount adequate to relieve symptoms after initiation 1

For Nausea and Vomiting

• Standard dose: 0.5 mg per pound of body weight (approximately 1 mg/kg) 1
• Adjust based on age, weight, and severity of condition 1
• May repeat 12.5-25 mg doses every 4-6 hours as necessary 1
• Important caveat: Antiemetics should not be used in vomiting of unknown etiology in children and adolescents 1

For Motion Sickness

• Dose: 12.5 to 25 mg twice daily 1
• Give initial dose one-half to one hour before anticipated travel 1
• Repeat 8-12 hours later if necessary 1

For Sedation

• Bedtime sedation: 12.5 to 25 mg at bedtime 1
• Preoperative sedation: 0.5 mg per pound of body weight in combination with appropriately reduced doses of narcotic or barbiturate and atropine-like drug 1
• Postoperative sedation: 12.5 to 25 mg 1

Important Safety Considerations

Adverse Effects Profile

• Promethazine can cause significant sedation, agitation, hallucinations, seizures, and dystonic reactions 2
• First-generation antihistamines like promethazine have substantial anticholinergic effects 3
• If acute dystonic reactions occur, administer diphenhydramine 1-2 mg/kg or 25-50 mg parenterally 4

Formulation Considerations

• Available as tablets (12.5,25,50 mg), syrup (6.25 mg/5 mL), and rectal suppositories 3, 1
• Oral syrup is preferred over rectal suppositories when possible due to more consistent absorption 3

Common Pitfall

• The ease of administration as a syrup and its historical widespread use may lead to inappropriate use in children under 2 years—this must be avoided 2
• The sedation rate with promethazine is 60-73%, which is substantially higher than second-generation antihistamines 3