What is the appropriate intravenous (IV) morphine bolus dose and patient‑controlled analgesia (PCA) settings for an opioid‑naïve adult (or elderly) patient with acute pain?

IV Morphine Dosing for Opioid-Naïve Adults with Acute Pain

For opioid-naïve adults with acute pain, administer 1–5 mg IV morphine as the initial bolus, reassess every 15 minutes, and repeat with 50–100% dose escalation until pain is controlled (typically to a numeric rating ≤3/10). 1

Initial Bolus Dose

• Start with 2–3 mg IV morphine for most opioid-naïve adults with moderate-to-severe acute pain 2, 3
• Use 2 mg for patients ≤60 kg and 3 mg for patients >60 kg 3, 4
• Reduce the initial dose by 30–50% in elderly patients (≥70 years), starting with approximately 2 mg, due to decreased clearance and increased opioid sensitivity 2, 3
• Reduce to 25–50% of the usual dose in renal impairment to avoid accumulation of morphine-6-glucuronide, which causes neurotoxicity 2
• Administer each bolus slowly over 2–3 minutes to minimize adverse effects 5

Titration Protocol

• Reassess pain intensity every 15 minutes after each IV bolus 1, 2, 4
• If pain is unchanged or increased, administer 50–100% of the previous dose 1, 2
• If pain decreases to moderate level (4–6/10), repeat the same dose and reassess in 15 minutes 1, 2
• Continue titration until pain score is ≤3/10 or until sedation occurs (Ramsay score >1) 4
• There is no dose ceiling when titrating to symptoms during acute pain management 2
• The mean time to achieve significant analgesia is approximately 10 minutes, using a mean total dose of 8.5 mg IV morphine 6

Common Pitfall to Avoid

Do not use fixed 5-minute intervals between boluses without considering the patient's response—morphine's relative onset is approximately 6 minutes, but effect delay can extend to 1.6–4.8 hours in some patients, making 15-minute reassessment intervals more appropriate for safe titration. 7 However, boluses can be given every 5 minutes if pain remains severe and no sedation is present, as demonstrated in postoperative protocols. 3, 4

Patient-Controlled Analgesia (PCA) Settings

Once initial pain control is achieved with bolus titration:

• Calculate the total morphine dose used during titration and assume this will provide approximately 4 hours of analgesia 6
• PCA demand dose: 1 mg IV morphine (approximately 10–20% of the hourly requirement) 1
• Lockout interval: 5–10 minutes 4, 7
• Background infusion: generally not recommended for opioid-naïve patients to reduce risk of respiratory depression 1
• Reassess within 24 hours after establishing PCA settings, as steady state is reached within this timeframe 8

Monitoring Requirements

• Monitor respiratory rate, sedation level, and vital signs every 15–30 minutes during initial titration 2
• Bradypnea with marked somnolence is the primary warning sign requiring immediate dose reduction or cessation 9
• Oxygen saturation should be monitored continuously during titration 8
• Document the specific rationale for each dose (e.g., "for severe pain rated 8/10") 2

Supportive Care

• Initiate a prophylactic bowel regimen with stimulant laxatives simultaneously with morphine therapy 8, 2
• Order antiemetics pro re nata to manage opioid-induced nausea 8, 2
• For patients with a history of nausea, prophylactic antiemetic treatment is strongly recommended 8

Special Populations

Elderly Patients (≥70 years)

• Start with 2 mg IV morphine regardless of body weight 2, 3
• The same titration protocol (2–3 mg boluses every 5 minutes) can be safely applied to elderly patients, as total morphine requirements per kilogram are similar (0.14 vs. 0.15 mg/kg) and adverse effect rates are equivalent 3

Renal Impairment

• Start with 25–50% of the usual dose (1–1.5 mg IV) 2
• Consider alternative opioids (fentanyl, hydromorphone) in severe renal impairment (eGFR <30 mL/min) 8

Hepatic Impairment

• Use morphine cautiously and consider dose reduction, as hepatic impairment alters metabolism 2

Conversion to Oral Morphine

• Once pain is controlled and the 24-hour IV morphine requirement is stable, convert to oral morphine using a 1:3 ratio for low doses and 1:2 ratio for high doses 6
• Prescribe breakthrough doses equal to 10–20% of the total 24-hour oral morphine dose, available every 4 hours as needed 1, 8
• If the patient requires >3–4 breakthrough doses per day, increase the scheduled baseline dose by 25–50% 8

Critical Safety Considerations

• Never start with doses ≥20 mg in opioid-naïve patients, as this significantly increases adverse effects without proportional analgesic benefit 2
• Do not use extended-release formulations for opioid-naïve patients with acute pain 8
• Naloxone should be immediately available, diluted in normal saline and administered every 30–60 seconds until improvement if respiratory depression occurs 8
• Respiratory depression can occur at any time, particularly during initiation and after dose increases 8