What is the recommended dosing for Phenergan (promethazine)?

Phenergan (Promethazine) Dosing

For adults, the standard dose of promethazine is 12.5-25 mg, with the route and frequency depending on the indication: 25 mg orally/rectally/IV every 4-6 hours for nausea/vomiting, 25 mg twice daily for motion sickness, and 12.5-50 mg for sedation. 1

Adult Dosing by Indication

Nausea and Vomiting

• Standard dose: 25 mg, repeated every 4-6 hours as necessary 1
• Alternative dosing: 12.5 mg may be used and repeated at 4-6 hour intervals 1
• Low-dose option: 6.25-12.5 mg IV has been shown to be equally effective as ondansetron 4 mg, with 74% and 68% relief at one hour respectively, while minimizing sedation 2
• When oral medication cannot be tolerated, use parenteral or rectal routes 1

Motion Sickness

• Dosing: 25 mg twice daily 1
• Take the initial dose 30-60 minutes before anticipated travel 1
• Repeat 8-12 hours later if necessary 1
• On subsequent travel days: 25 mg upon arising and before evening meal 1

Allergies

• Standard dose: 25 mg at bedtime 1
• Alternative: 12.5 mg before meals and at bedtime if necessary 1
• Minimal effective dose: 6.25-12.5 mg three times daily usually suffices 1
• For minor transfusion reactions: 25 mg single dose 1

Sedation

• Nighttime/presurgical sedation: 25-50 mg 1
• Preoperative: 50 mg the night before surgery 1
• Postoperative: 25-50 mg with appropriately reduced narcotic/barbiturate doses 1

Pediatric Dosing

Critical Safety Warning

• Promethazine is contraindicated in children under 2 years of age due to risk of fatal respiratory depression 1
• Use the smallest effective dose in children to minimize risks 1

Pediatric Doses by Indication

• Nausea/vomiting: 0.5 mg per pound of body weight, adjusted for age and severity 1
• Motion sickness: 12.5-25 mg twice daily 1
• Sedation: 12.5-25 mg at bedtime 1
• Preoperative: 0.5 mg per pound with reduced narcotic/barbiturate and atropine-like drug 1
• Postoperative: 12.5-25 mg 1

Route-Specific Considerations

Intravenous Administration

• Lower doses (6.25-12.5 mg IV) provide equivalent antiemetic efficacy to standard 25 mg doses while reducing sedation 2
• This is particularly important when combining with narcotic analgesics 2

Comparative Efficacy

• Prochlorperazine 10 mg IV is significantly more effective than promethazine 25 mg IV for nausea/vomiting, with faster time to complete relief and fewer treatment failures (9.5% vs 31%) 3
• Promethazine causes significantly more sedation (71% vs 38% with prochlorperazine) 3

Important Clinical Considerations

Dose adjustment principle: Always titrate to the smallest amount adequate to relieve symptoms after treatment initiation 1

Duration considerations: After 10 days of use, doses do not need to be tapered 1

Contraindication for unknown etiology: Antiemetics should not be used for vomiting of unknown cause in children and adolescents 1