What is the recommended dosage of promethazine (Phenergan) for dispensing?

Recommended Dosage for Promethazine (Phenergan)

The recommended dosage of promethazine (Phenergan) for dispensing is 12.5 to 25 mg for most adults, with a frequency of every 4-6 hours as needed, and a maximum of 25 mg per dose or 100 mg in 24 hours. 1

Dosage by Indication

Nausea and Vomiting

• Standard adult dose: 25 mg every 4-6 hours as needed 1
• Lower dose option: 12.5 mg every 4-6 hours as needed 1
• Elderly patients: 6.25-12.5 mg every 6 hours as needed 2, 3
• Maximum daily dose: 100 mg (four 25 mg doses) 1

Allergy

• Standard dose: 25 mg at bedtime 1
• Alternative dosing: 12.5 mg before meals and at bedtime if necessary 1

Motion Sickness

• Initial dose: 25 mg 30-60 minutes before travel 1
• Maintenance: 25 mg every 8-12 hours as needed 1
• For extended travel: 25 mg upon waking and before evening meal 1

Sedation

• Adults: 25-50 mg at bedtime 1
• Children: 12.5-25 mg at bedtime (contraindicated under 2 years) 1

Special Populations

Elderly Patients

• Start with 6.25 mg for elderly patients due to:
  • Increased sensitivity to anticholinergic effects
  • Higher risk of sedation and confusion
  • Altered drug metabolism and elimination
  • Increased risk of extrapyramidal side effects 2, 3
• Research shows 6.25 mg IV is as effective as higher doses with fewer adverse effects in elderly patients 3

Children

• Contraindicated in children under 2 years of age 1
• For children over 2 years: 0.5 mg per pound of body weight 1

Administration Considerations

• Oral administration: Take with food to reduce gastrointestinal irritation 2
• IV administration: Administer slowly (maximum 25 mg/min) to minimize hypotension risk 4
• Duration of action: 4-6 hours, but may be prolonged in elderly patients 2
• Onset of action: Within 5 minutes for IV administration; may be delayed with oral administration 2

Efficacy and Safety Considerations

• Low-dose promethazine (6.25 mg IV) has been shown to be as effective as ondansetron 4 mg IV for nausea and vomiting relief 5
• The anticholinergic effects of promethazine may provide better control of rhinorrhea compared to second-generation antihistamines 4
• Common adverse effects include sedation, dry mouth, urinary retention, blurred vision, extrapyramidal symptoms, and hypotension 2

Dispensing Recommendations

1. For most adults: Dispense 25 mg tablets with instructions to take 1 tablet every 4-6 hours as needed, not to exceed 4 tablets in 24 hours
2. For elderly patients: Consider dispensing 12.5 mg tablets (or scored 25 mg tablets with instructions to take half) every 6 hours as needed
3. For prolonged therapy: Dispense the smallest amount adequate to relieve symptoms 1
4. For patients with risk of adverse effects: Consider alternative antiemetics with fewer anticholinergic effects 2

Remember to counsel patients about potential sedative effects and to avoid alcohol and other CNS depressants while taking promethazine.