What is the recommended IV (intravenous) morphine dosage for an 11-year-old patient weighing 51 kg?

IV Morphine Dosing for an 11-Year-Old Weighing 51 kg

For an 11-year-old child weighing 51 kg, administer IV morphine at 0.05-0.1 mg/kg per dose (2.5-5 mg), infused over 10 minutes, which can be repeated every 15 minutes as needed for breakthrough pain. 1

Initial Dosing Strategy

Start with 2.5-5 mg IV morphine (0.05-0.1 mg/kg) as the initial bolus dose. 2, 1 This weight-based approach provides the foundation for safe and effective pain control in pediatric patients.

• The American Academy of Pediatrics specifically recommends 0.05-0.1 mg/kg IV for children, with infusion over 10 minutes 1
• For this 51 kg patient, the calculated dose range is 2.5-5 mg IV 1
• The maximum initial single dose should not exceed 1 mg when treating specific conditions like infundibular spasm, but for general acute pain management, higher doses within the weight-based range are appropriate 2

Titration Protocol

Reassess pain at 15-minute intervals and repeat the same dose if inadequate relief is achieved. 1

• Breakthrough doses should equal the regular 4-hourly scheduled dose 1
• For immediate pain control in acute settings, doses of 0.025-0.1 mg/kg IV can be titrated to effect 1
• The Society of Critical Care Medicine supports repeating doses every 15 minutes as needed for breakthrough pain 1

Age-Specific Pharmacokinetic Considerations

Children under 11 years have significantly higher morphine clearance (23.1 mL/min/kg) and larger volume of distribution (5.2 L/kg) compared to older children and adults. 3

• An 11-year-old sits at the transition point where pharmacokinetics begin to approach adult values 3
• This patient may require doses toward the higher end of the weight-based range due to potentially faster clearance 3
• Plasma morphine concentrations above 12 ng/mL are associated with better pain control in children 3

Monitoring Requirements

Monitor respiratory rate, oxygen saturation, and sedation level continuously for at least 2 hours after each dose. 2

• Be prepared to provide respiratory support, as morphine can cause respiratory depression 2
• Naloxone (0.1 mg/kg IV) should be immediately available for reversal of opioid-induced respiratory depression 2
• Watch for common side effects including nausea (occurs in up to two-thirds of patients initially), drowsiness, and constipation 2

Common Pitfalls to Avoid

Do not use the adult dose of 0.1 mg/kg as a single bolus without titration, as research shows this dose is inadequate for controlling severe acute pain in 67% of patients. 4

• Starting with lower doses (0.05 mg/kg) and titrating upward provides safer pain control 5
• Avoid intramuscular administration when IV access is available, as IV provides faster onset (5 minutes vs 20 minutes) and better initial analgesia 6
• Do not administer morphine to patients whose mothers have long-term opioid use due to risk of acute withdrawal and seizures 2

Route Conversion Reference

If transitioning from IV to oral morphine, use a 1:3 ratio (oral dose is 3 times the IV dose). 2, 1

• The oral to IV potency ratio is 1:2 to 1:3, meaning 20-30 mg oral morphine equals approximately 10 mg IV 2
• Subcutaneous administration is the preferred alternative if oral route is unavailable, using the same 1:2 to 1:3 conversion 2

Practical Dosing Algorithm for This Patient

1. Initial dose: Administer 2.5-5 mg IV morphine over 10 minutes 2, 1
2. Assessment: Evaluate pain score at 15 minutes using standardized pain scale 1
3. Repeat dosing: If pain remains severe, give another 2.5-5 mg IV 1
4. Ongoing management: Continue q15min dosing until pain controlled, then establish regular 4-hourly schedule 1
5. Daily review: Assess total 24-hour morphine consumption and adjust regular doses accordingly 1