What is the dose conversion ratio of oral (PO) morphine (M) to oral hydromorphone (HM) in the management of chronic pain?

Oral Morphine to Oral Hydromorphone Conversion Ratio

The conversion ratio from oral morphine to oral hydromorphone for chronic pain management is 5:1, meaning 30 mg of oral morphine is approximately equivalent to 6 mg of oral hydromorphone. 1

Primary Conversion Ratio

• The most widely supported conversion ratio in clinical practice guidelines is 5:1 (oral morphine to oral hydromorphone). 1, 2
• The NCCN guidelines explicitly demonstrate this ratio in their conversion tables, showing that 60 mg oral morphine daily equals 15 mg oral hydromorphone daily, and 120 mg oral morphine equals 30 mg oral hydromorphone. 1
• The FDA label for hydromorphone confirms that 5 mg and 10 mg of oral hydromorphone provided comparable pain relief to 30 mg and 60 mg of oral morphine, respectively, supporting the 5:1 to 6:1 ratio. 3

Evidence Supporting Alternative Ratios

• A systematic review found consistent data supporting the 5:1 conversion ratio between oral morphine and oral hydromorphone across multiple studies. 2
• Some research studies have explored an 8:1 ratio (oral morphine to oral hydromorphone), with one prospective evaluation of 343 patients finding this ratio clinically useful during conversion. 4
• A Japanese randomized controlled trial compared 5:1 versus 8:1 ratios and found both effective, with pain control ratios of 83.3% (5:1 group) and 95.0% (8:1 group), though the 8:1 ratio may provide more conservative dosing. 5

Clinical Application Algorithm

When converting from oral morphine to oral hydromorphone:

1. Calculate the total 24-hour oral morphine dose. 1

2. Divide the total daily morphine dose by 5 to obtain the equianalgesic hydromorphone dose. 1, 2

3. Reduce the calculated hydromorphone dose by 25-50% to account for incomplete cross-tolerance between opioids. 1

   • Use a 25% reduction if pain was well-controlled on morphine
   • Use a 50% reduction for safer, more conservative conversion

4. Divide the total daily hydromorphone dose by the dosing frequency (e.g., every 4 hours for immediate-release or every 12 hours for extended-release formulations). 1

5. Prescribe immediate-release hydromorphone for breakthrough pain at 10-15% of the total daily dose. 6

Practical Example

For a patient taking 60 mg oral morphine daily:

• Step 1: Total daily morphine = 60 mg 1
• Step 2: 60 mg ÷ 5 = 12 mg oral hydromorphone (equianalgesic dose) 1
• Step 3: 12 mg × 0.75 (25% reduction) = 9 mg oral hydromorphone daily, OR 12 mg × 0.5 (50% reduction) = 6 mg oral hydromorphone daily 1
• Step 4: For extended-release: 4.5 mg every 12 hours (or 3 mg every 12 hours for more conservative approach) 1
• Step 5: Breakthrough dose: 1-1.5 mg immediate-release hydromorphone as needed 6

Critical Safety Considerations

• Monitor patients closely during the first 48-72 hours after conversion for both adequate pain control and adverse effects (sedation, respiratory depression, nausea). 1, 4
• The 5:1 ratio is a starting point; individual dose adjustments are frequently required. In one study, 54% of patients required dose increases after initial conversion, while 43% remained stable on the initial converted dose. 4
• If pain was poorly controlled on morphine, consider starting with 100% of the equianalgesic dose (no reduction) or even increasing by 25%. 1
• In renal impairment, use hydromorphone with caution at reduced doses and frequency, though it has less problematic metabolite accumulation compared to morphine. 1, 6

Common Pitfalls to Avoid

• Do not use fixed conversion ratios without clinical judgment—patient variability means these are approximate guides requiring individualized titration. 1, 2
• Do not forget to account for incomplete cross-tolerance—failing to reduce the dose by 25-50% when switching opioids can lead to overdosing. 1, 2
• Do not neglect breakthrough medication—patients need rescue doses during and after conversion, particularly in the first 24-48 hours. 1
• Do not assume the 8:1 ratio is safer for all patients—while more conservative, it may result in inadequate pain control and require more frequent titration steps. 5, 4