Promethazine Oral Solution Dosing for 25 mg
For a 25 mg dose of promethazine oral solution, the pharmacy should dispense 10 mL (10 milliliters).
Dosage Calculation Explanation
Promethazine oral solution is typically available in a concentration of 6.25 mg/5 mL. Therefore:
- For a 25 mg dose:
- 6.25 mg = 5 mL
- 25 mg = (25 ÷ 6.25) × 5 mL = 4 × 5 mL = 20 mL
However, based on more recent guidelines and clinical practice, promethazine is also commonly available in a concentration of 25 mg/10 mL 1. Using this concentration:
- 25 mg = 10 mL
Clinical Context
Promethazine is a phenothiazine derivative with antihistamine, sedative, antiemetic, and anticholinergic effects. It's commonly used for:
- Management of nausea and vomiting
- Sedation for procedures
- Adjunct to analgesia
- Treatment of allergic conditions
Administration Considerations
- The clinical effects of promethazine are evident within 5 minutes of intravenous administration, but may be delayed with oral administration 1
- Duration of action is 4-6 hours, and the plasma half-life is 9-16 hours 1, 2
- For oral administration, the medication can be taken with food to reduce gastrointestinal irritation 3
Dosing Considerations
- Standard adult dosing for promethazine is 12.5 to 25 mg 1, 3
- Lower doses (12.5 mg) are recommended for elderly patients due to increased sensitivity to anticholinergic effects 3
- Maximum recommended dose is typically 25 mg in 24 hours for elderly patients 3
Important Precautions
- Promethazine has sedative properties and may cause drowsiness
- It should be used with caution when combined with other CNS depressants
- Common adverse effects include sedation, anticholinergic effects (dry mouth, urinary retention, blurred vision), extrapyramidal symptoms, and hypotension 3
- Promethazine should be used with caution in patients with respiratory conditions, as it may cause respiratory depression
Remember that accurate measurement of liquid medications is essential for proper dosing. The pharmacy should provide an appropriate measuring device if the patient will be self-administering the medication at home.