What is a reasonable conversion dose from morphine (Morphine) 30mg orally (PO) every 4 hours (Q4h) to hydromorphone (Hydromorphone) for a patient, considering their individual characteristics such as age, weight, and medical history, including potential impaired renal function?

Morphine to Hydromorphone Conversion

Convert morphine 30mg PO Q4h to hydromorphone 6mg PO Q4h, then reduce by 25-50% to account for incomplete cross-tolerance, resulting in a starting dose of hydromorphone 3-4.5mg PO Q4h.

Conversion Calculation

Step 1: Calculate Total Daily Morphine Dose

• Morphine 30mg Q4h = 6 doses per 24 hours 1
• Total daily morphine = 30mg × 6 = 180mg per day 1

Step 2: Apply Oral Morphine to Oral Hydromorphone Ratio

• The standard conversion ratio is 5:1 (oral morphine to oral hydromorphone) 2, 3, 4, 5
• Some sources suggest hydromorphone is 5-7 times more potent than morphine, but the 5:1 ratio is most consistently recommended across guidelines 2, 3
• Calculated hydromorphone dose = 180mg ÷ 5 = 36mg per day 4, 5

Step 3: Divide into Q4h Dosing

• 36mg per day ÷ 6 doses = 6mg Q4h 1

Step 4: Apply Incomplete Cross-Tolerance Reduction

• Reduce the calculated dose by 25-50% to account for incomplete cross-tolerance 2, 6
• This is a critical safety step when converting between opioids, even when pain is well-controlled 6
• Final starting dose range: 3-4.5mg PO Q4h 2, 6

Dosing Recommendations Based on Clinical Context

If Pain Was Well-Controlled on Morphine

• Start with 3mg PO Q4h (50% reduction) 6
• This conservative approach minimizes risk of oversedation while maintaining adequate analgesia 6

If Pain Was Poorly Controlled on Morphine

• Start with 4.5mg PO Q4h (25% reduction) or consider using the full calculated dose of 6mg 6
• The higher end of the range is appropriate when converting due to inadequate pain control 6

Breakthrough Dosing

• Prescribe immediate-release hydromorphone for breakthrough pain equal to 10-20% of the total 24-hour dose 2
• For a patient on 18-27mg per day, breakthrough doses should be 2-5mg 2
• Alternatively, the breakthrough dose can equal the regular 4-hourly dose (3-4.5mg in this case) 2

Special Population Adjustments

Renal Impairment

• Start with one-fourth to one-half the calculated dose 2, 6
• Hydromorphone is safer than morphine in renal failure, but active metabolites can still accumulate 2
• For a patient with renal impairment, start with 1.5-2.25mg PO Q4h 2

Hepatic Impairment

• Reduce the initial dose by 25-50% (one-fourth to one-half the usual dose) 2, 6
• Hydromorphone undergoes glucuronidation, which may be impaired in hepatic dysfunction 2
• Start with 1.5-3mg PO Q4h in hepatic impairment 2, 6

Mandatory Concurrent Prescriptions

Bowel Regimen

• Institute a stimulant laxative (senna) prophylactically in all patients receiving hydromorphone unless contraindicated 2, 6, 1
• Constipation is universal with opioid therapy and must be prevented, not just treated 6, 1
• Increase laxative dose when escalating opioid dose 1

Antiemetic Prophylaxis

• For patients with a history of opioid-induced nausea, prescribe prophylactic antiemetics 2

Monitoring and Titration

Initial Monitoring

• Reassess pain control and adverse effects within 24 hours after conversion 6
• Steady state is reached within 24 hours after dose adjustment 2, 6

Dose Titration Strategy

• If more than 3-4 breakthrough doses are required per day, increase the scheduled baseline dose by 25-50% rather than shortening the dosing interval 2, 6
• When pain returns consistently before the next dose, increase the dose rather than the frequency 2
• There is no advantage to dosing more frequently than Q4h for immediate-release hydromorphone 2

Critical Safety Considerations

Respiratory Depression

• Monitor oxygen saturation closely, particularly during initiation and after dose increases 2
• Have naloxone readily available; dilute in normal saline and administer every 30-60 seconds until improvement 2

Common Pitfall to Avoid

• Do not use the full calculated equianalgesic dose without reduction for incomplete cross-tolerance 2, 6
• This is the most common error in opioid conversion and can lead to oversedation and respiratory depression 6
• Always reduce by at least 25% when converting between opioids 2, 6