What is the recommended dose of promethazine (Phenergan) for adults and children?

Recommended Dosage of Promethazine (Phenergan) for Adults and Children

The recommended dose of promethazine for adults is 12.5 to 25 mg every 4-6 hours, with a maximum of 25-50 mg in 24 hours, while children over 2 years should receive 0.5 mg/kg/dose (12.5-25 mg) every 4-6 hours as needed; promethazine is contraindicated in children under 2 years of age. 1, 2, 3

Adult Dosing Guidelines

General Dosing

• Starting dose: 12.5 mg for most adults 3
• Usual dose range: 12.5-25 mg 2
• Maximum dose: 25-50 mg in 24 hours 3, 1
• Dosing interval: Every 4-6 hours as needed 1
• Administration: Can be given orally, intravenously (IV), or as rectal suppository 1

Indication-Specific Dosing for Adults

1. Nausea and Vomiting:

   • 25 mg every 4-6 hours as needed
   • When oral medication cannot be tolerated, use parenteral route or rectal suppository 1

2. Allergy:

   • 25 mg before bedtime, or
   • 12.5 mg before meals and at bedtime if necessary 1

3. Motion Sickness:

   • 25 mg twice daily
   • Initial dose: 30-60 minutes before travel
   • Repeat dose 8-12 hours later if needed
   • On subsequent travel days: 25 mg upon waking and before evening meal 1

4. Sedation:

   • 25-50 mg at bedtime for nighttime, presurgical, or obstetrical sedation 1

Pediatric Dosing Guidelines

Important Safety Warning

• Contraindicated in children under 2 years of age due to risk of respiratory depression, seizures, and potential association with sudden infant death syndrome 1, 4

General Dosing for Children (≥2 years)

• Usual dose: 0.5 mg/kg per dose 1
• Typical range: 12.5-25 mg per dose 2
• Maximum: Should not exceed adult dosing
• Frequency: Every 4-6 hours as needed 1

Indication-Specific Dosing for Children (≥2 years)

1. Nausea and Vomiting:

   • 0.5 mg/kg per dose, adjusted to age and weight 1

2. Motion Sickness:

   • 12.5-25 mg twice daily 1

3. Sedation:

   • 12.5-25 mg at bedtime 1

Special Populations

Elderly Patients

• Recommended starting dose: 6.25 mg 3, 5
• Maximum dose: 25 mg in 24 hours 3
• Rationale: Lower doses are equally effective with fewer adverse effects in elderly patients 5, 6
• Research shows 6.25 mg IV is as effective as 12.5 mg for treating nausea with significantly fewer adverse effects 5

Administration Considerations

Intravenous Administration

• Infusion rate: Administer slowly (25 mg/min) to minimize risk of hypotension 2
• Dilution: Should be diluted appropriately
• Monitoring: Monitor for hypotension during IV administration

Timing Considerations

• Onset of action: Within 5 minutes for IV administration 2, 3
• Duration of action: 4-6 hours 2, 3
• Half-life: 9-16 hours in adults, potentially longer in elderly patients 2, 3

Adverse Effects and Precautions

Common Adverse Effects

• Sedation (most common)
• Anticholinergic effects (dry mouth, urinary retention, blurred vision)
• Hypotension
• Dizziness
• Respiratory depression 2, 3

Serious Adverse Effects

• Extrapyramidal symptoms
• Neuroleptic malignant syndrome
• Tissue necrosis with extravasation
• Respiratory depression (especially when combined with other CNS depressants) 2, 3

Common Pitfalls to Avoid

1. Using in children under 2 years - absolutely contraindicated 1, 4
2. Failing to reduce dosage in elderly patients - increases risk of adverse effects 3, 5
3. Rapid IV administration - can cause severe hypotension 2
4. Not recognizing drug-drug interactions - especially with other CNS depressants 3
5. Using standard adult dosing in elderly patients - significantly increases adverse effect risk 3

Alternative Treatment Options

For patients with contraindications to promethazine, consider:

• Ondansetron 4 mg (fewer anticholinergic effects)
• Prochlorperazine 10 mg PO every 6 hours
• Haloperidol 0.5-1 mg PO every 6-8 hours 3

By following these dosing guidelines and being aware of the contraindications and precautions, promethazine can be safely and effectively used for managing nausea, vomiting, allergies, and as a sedative in appropriate patient populations.