What is the dosage signature for promethazine in adults?

Promethazine Dosage for Adults

The recommended dosage of promethazine for adults is 12.5-25 mg orally every 6 hours as needed, with a maximum of 25 mg per dose. 1

General Dosing Guidelines

Oral Administration

• Starting dose: 12.5 mg for most adults
• Maximum single dose: 25 mg
• Frequency: Every 6 hours as needed
• Maximum daily dose: 100 mg (25 mg four times daily)

Indication-Specific Dosing

Allergy

• 25 mg before bedtime, or
• 12.5 mg three times daily (before meals and at bedtime) 1

Nausea and Vomiting

• 12.5-25 mg every 4-6 hours as needed 1
• Low-dose promethazine (6.25 mg) has been shown to be as effective as 12.5 mg for controlling nausea and vomiting while causing less sedation 2, 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

Sedation

• 12.5-25 mg at bedtime for mild sedation
• 25-50 mg for nighttime, pre-surgical, or obstetrical sedation 1

Special Populations

Elderly Patients

• Recommended starting dose: 6.25-12.5 mg
• Maximum daily dose: 25 mg in 24 hours 4
• Lower doses are recommended due to:
  • Increased sensitivity to anticholinergic effects
  • Higher risk of sedation and confusion
  • Altered drug metabolism and elimination
  • Increased risk of extrapyramidal side effects 4, 5

Administration Considerations

• Take with food to reduce gastrointestinal irritation 4
• Ensure adequate hydration during treatment 4
• Onset of action: Within 5 minutes for IV administration, delayed with oral administration
• Duration of action: 4-6 hours (may be prolonged in elderly patients) 4

Common Adverse Effects

• Sedation (most common)
• Anticholinergic effects (dry mouth, urinary retention, blurred vision)
• Extrapyramidal symptoms
• Hypotension
• CNS depression (especially when combined with other CNS depressants) 4

Important Precautions

• Avoid using in children under 2 years of age (contraindicated) 1
• Use caution when combining with other CNS depressants
• Monitor for excessive sedation, especially in elderly patients 4
• Consider lower doses (6.25 mg) in elderly patients, as studies show equal efficacy with fewer adverse effects compared to standard doses 5

Alternative Antiemetics

When promethazine is contraindicated or poorly tolerated, consider:

• Ondansetron 4 mg
• Prochlorperazine 10 mg every 6 hours
• Haloperidol 0.5-1 mg every 6-8 hours 6, 4