Which is stronger, hydromorphone or morphine, for an adult patient with no significant medical history?

Hydromorphone is Stronger Than Morphine

Hydromorphone is 5-10 times more potent than morphine when given orally and approximately 8.5 times more potent when administered intravenously. 1, 2

Potency Comparison

The equianalgesic dosing demonstrates this potency difference clearly:

• Intravenous route: 1.5 mg hydromorphone = 10 mg morphine 1
• Oral route: Hydromorphone is approximately 5 times more potent than morphine 2
• Parenteral route: The conversion ratio is approximately 1:8.5 2

Clinical Advantages of Hydromorphone's Greater Potency

Faster Onset and Reduced Dose-Stacking Risk

• Hydromorphone has a quicker onset of action compared to morphine 3, 1, 4
• The faster onset reduces the risk of dose stacking that occurs with morphine's longer onset of action 1, 4
• Morphine's longer onset places patients at higher risk for toxicity, hypoventilation, or inadequate analgesia when doses are stacked 3, 1

Psychological Prescribing Advantage

• Because hydromorphone requires much smaller milligram doses (1.5 mg vs 10 mg), physicians may be more likely to adequately treat pain rather than underdosing out of concern about giving "large" doses 3, 1
• This addresses the common clinical problem where physicians hesitate to give more than 5 mg of morphine and often give inadequate 2.5 mg doses 3

Renal Safety Profile

• Hydromorphone may be safer in renal failure due to morphine's greater risk of toxic metabolite accumulation 1, 4
• Both drugs should be used cautiously in patients with fluctuating renal function, but morphine-6-glucuronide accumulation poses particular concern 3
• However, hydromorphone's metabolite may be more neurotoxic than morphine's metabolite, requiring careful monitoring 3, 4

Comparative Efficacy and Side Effects

Analgesic Efficacy

• Meta-analysis suggests hydromorphone provides slightly better clinical analgesia than morphine, though the effect size is small 5
• For cancer pain management, both drugs show no major differences in efficacy when dosed equianalgesically 3, 1, 6
• A Cochrane review found hydromorphone and morphine to be clinically interchangeable for cancer-related pain 3

Adverse Effect Profile

• Side effects are generally similar between the two drugs when used in equianalgesic doses 1, 5, 6
• Some evidence suggests hydromorphone may cause less pruritus, sedation, nausea, and vomiting compared to morphine 2
• Hydromorphone causes little or no histamine release, making it safer for patients with type 2 allergies to morphine (urticaria, pruritus, facial flushing) 3, 4

Clinical Recommendations by Setting

Emergency Department and Acute Pain

For acute severe pain in the emergency department, hydromorphone (0.015 mg/kg IV) is recommended as comparable or potentially superior to morphine (0.1 mg/kg IV) 1

• This represents a strong recommendation with moderate quality evidence 3, 1
• The 1 mg + 1 mg patient-driven protocol with hydromorphone is preferred over standard morphine dosing 3

Cancer Pain Management

• Oral morphine remains the opioid of first choice for moderate to severe cancer pain 3
• Hydromorphone is an effective alternative to oral morphine and can be used interchangeably 3
• Both drugs have properties that make them suitable for cancer pain, with morphine being more widely available and less expensive 3

Acute Pancreatitis

• Most institutions prefer hydromorphone over morphine or fentanyl in non-intubated patients with acute pancreatitis 4
• First-line approach includes hydromorphone 0.015 mg/kg IV with patient-controlled analgesia option 4

Practical Considerations

• Hydromorphone is comparable in cost to morphine 3, 1
• Hydromorphone is more soluble than morphine, allowing smaller volume injections for parenteral administration 1
• The oral-to-parenteral conversion ratio is 1:2 to 1:3 for both drugs 3, 1

Common Pitfalls to Avoid

• Do not assume equal milligram dosing: Always use the 5-10:1 oral ratio or 8.5:1 IV ratio when converting between drugs 1, 2
• Monitor for neurotoxicity in renal impairment: Both drugs accumulate toxic metabolites, but hydromorphone's may be more neurotoxic 3, 4
• Avoid underdosing: Take advantage of hydromorphone's smaller milligram requirements to provide adequate analgesia 3, 1