What are the recommended IV medications for acute pain management?

IV Medications for Acute Pain Management

For acute moderate-to-severe pain in the emergency department, fentanyl (1 mcg/kg IV, then ~30 mcg every 5 minutes) is recommended over morphine, while hydromorphone (0.015 mg/kg IV) is recommended as comparable or potentially superior to morphine (0.1 mg/kg IV) for acute severe pain. 1

Opioid Selection by Pain Severity

Moderate-to-Severe Pain: Fentanyl vs. Morphine

Fentanyl is the preferred first-line IV opioid for the following reasons 1:

• Faster onset of action due to higher lipid solubility and 100-fold greater potency than morphine 1
• No cross-reactivity in patients with morphine allergies 1
• Better suited for rapid titration in acute settings with time to peak effect of 4.7-6.6 minutes 2
• Equivalent cost to morphine 1

Dosing: Start with 1 mcg/kg IV, then administer approximately 30 mcg every 5 minutes until adequate analgesia is achieved 1

If morphine is used instead, dose at 0.1 mg/kg IV initially, then 0.05 mg/kg at 30 minutes, with a maximum suggested dose of 10 mg 1, 3. The FDA-approved dosing range is 0.1-0.2 mg/kg every 4 hours as needed 3.

Severe Pain: Hydromorphone vs. Morphine

Hydromorphone is strongly recommended as comparable or potentially superior to morphine for acute severe pain 1:

• Quicker onset of action compared to morphine 1
• Lower risk of dose stacking and subsequent toxicity, particularly in renal failure 1
• Reduced risk of oligoanalgesia because physicians may be more willing to administer an appropriate dose of 1.5 mg hydromorphone versus 10 mg morphine 1
• Comparable cost to morphine 1

Dosing: 0.015 mg/kg IV for hydromorphone versus 0.1 mg/kg IV for morphine 1

Patient-Driven Protocols

A hydromorphone 1 mg + 1 mg patient-driven protocol is recommended over physician-driven protocols with other IV opioids 1. This approach is particularly beneficial for:

• Patients unable to clearly communicate pain levels 1
• Patients with acute mental status changes 1
• Non-English speaking patients 1

Special Populations and Considerations

Renal Impairment

Fentanyl is the safest opioid choice in patients with chronic kidney disease stages 4-5 (eGFR <30 mL/min) 1:

• Can be administered IV or transdermally 1
• Does not accumulate toxic metabolites like morphine-6-glucuronide 1
• Buprenorphine is an alternative option 1

For all opioids in renal impairment: Start with lower doses and reduced frequency, titrating slowly while monitoring for side effects 1, 3

Rapid IV Titration for Severe Cancer Pain

IV morphine titration provides the fastest pain relief when severe pain requires urgent control 1:

• Administer 1.5 mg IV bolus every 10 minutes until pain relief or adverse effects occur 1
• 84% of patients achieve satisfactory pain relief within 1 hour versus 25% with oral immediate-release morphine 1
• After stabilization, convert to oral or other routes 1

Pediatric Considerations

IV opioids are appropriate for pediatric acute pain with the following caveats 1:

• Small titrated doses can provide pain relief without affecting clinical examination or neurologic assessments 1
• Pain medication does not mask symptoms or cloud mental status in children with abdominal pain or trauma 1
• Alternative routes (intranasal, transmucosal) may be considered when IV access is not established 1

Critical Safety Warnings

Respiratory Depression Risk

Respiratory depression is the primary risk with all IV opioids 3:

• Higher risk in elderly, debilitated patients, and those with COPD, hypoxia, or hypercapnia 3
• Rapid IV administration may cause chest wall rigidity 3
• Naloxone and resuscitative equipment must be immediately available 3
• Administration should be limited to providers familiar with managing respiratory depression 3

Dosing Error Prevention

Take extreme care to avoid confusion between different concentrations and between mg and mL 3:

• Always prescribe both total dose in mg AND total volume 3
• Morphine is available in multiple concentrations for direct injection 3
• Dosing errors can result in accidental overdose and death 3

Common Pitfalls to Avoid

• Do not use transdermal fentanyl for acute pain or rapid titration - it has a 17-48 hour delay to maximum plasma concentration and is contraindicated in acute postoperative pain 4, 5
• Do not underdose hydromorphone - the smaller milligram amount (1.5 mg vs 10 mg morphine) may lead to psychological barriers to adequate dosing 1
• Do not assume morphine is always first-line - fentanyl and hydromorphone have specific advantages in the acute setting 1
• Do not forget that pain control aids diagnosis - adequate analgesia makes physical examination easier and does not interfere with diagnostic accuracy 1