Converting Short-Acting Morphine to Long-Acting Morphine
The equivalent long-acting morphine dose for a patient taking 27.5 mg of short-acting morphine orally in 24 hours is 27.5 mg of long-acting morphine divided into either two 12-hour doses (13.75 mg every 12 hours) or a single 24-hour dose depending on the formulation used.
Conversion Principles
When converting from short-acting to long-acting morphine:
Calculate the total 24-hour morphine requirement
- In this case, the patient is already taking 27.5 mg of short-acting morphine PO in 24 hours
Use a 1:1 conversion ratio
- For the same drug (morphine to morphine), the total daily dose remains the same
- No dose adjustment is needed when converting between immediate-release and extended-release formulations of the same opioid 1
Determine dosing schedule based on formulation
- For 12-hour formulations: Divide the total daily dose by 2
- For 24-hour formulations: Give the entire daily dose once daily
Dosing Options
12-hour extended-release morphine:
- 13.75 mg every 12 hours (rounded from 13.75 mg)
- May need to round to nearest available dosage form (e.g., 15 mg every 12 hours)
24-hour extended-release morphine:
- 27.5 mg once daily
- May need to round to nearest available dosage form
Important Considerations
Breakthrough Pain Management
- Continue to provide short-acting morphine for breakthrough pain
- Breakthrough dose should be 10-20% of the 24-hour oral morphine dose 1
- For this patient, appropriate breakthrough dose would be approximately 3-5.5 mg of immediate-release morphine
Monitoring
- Assess pain control throughout the dosing interval
- If pain returns consistently before the next regular dose, the regular dose should be increased 1
- Most patients achieve adequate pain control with 12-hour dosing, but some may require 8-hour dosing 1
Side Effect Management
- Constipation is the most common side effect that does not improve over time
- Prophylactic laxative regimen is essential (stool softener plus stimulant laxative) 1
- Titrate laxative dose when increasing opioid dose
Common Pitfalls to Avoid
Failing to maintain the same total daily dose when converting between immediate-release and extended-release formulations of the same drug
Not providing breakthrough medication - Even with stable long-acting dosing, breakthrough pain may occur and requires management with short-acting opioids
Changing between different modified-release products - Although guidelines suggest there are no substantial differences between 12-hour formulations, it's generally best to maintain consistency with a specific product 1
Inadequate monitoring during transition - The first 24-48 hours after conversion require careful monitoring to ensure adequate pain control and manage any side effects
By following these principles, the transition from short-acting to long-acting morphine can be accomplished safely while maintaining effective pain control.