Safe Starting Dose of Morphine for a 22kg Male
For a 22kg male, the safe starting dose of morphine is 0.1 mg/kg intravenously, which equals approximately 2.2 mg IV, or 5-10 mg orally for opioid-naïve patients.
Dosing Considerations Based on Weight and Route
The appropriate dosing of morphine depends on several factors, including:
- Patient's weight
- Route of administration
- Prior opioid exposure
- Severity of pain
Intravenous Dosing
- Standard pediatric dose for severe pain: 0.1 mg/kg IV 1
- For a 22kg patient: 2.2 mg IV (can be rounded to 2.5 mg for practical administration)
- Peak plasma concentration reached within 15-60 minutes 1
Oral Dosing
- For opioid-naïve patients: 5 mg oral morphine every 4 hours 2
- For patients previously on weak opioids: 10 mg oral morphine every 4 hours 2
- Oral-to-IV potency ratio is approximately 1:3 1
- Therefore, oral equivalent of 2.2 mg IV would be approximately 6.6 mg
Dosing Schedule and Titration
- Immediate-release morphine should be administered every 4 hours 1
- Elimination half-life of morphine is 2-4 hours 1
- Duration of analgesia is approximately 4 hours 1
- Steady state is reached within 4-5 half-lives (8-20 hours) 1
Titration Protocol
- Start with recommended dose based on weight and opioid exposure
- Allow for breakthrough doses of the same amount as the regular dose
- Assess pain control after 3-5 days
- Adjust dose as needed based on response
Studies have shown significant reduction in pain scores after 3 and 5 days from baseline using this approach 2.
Special Considerations and Monitoring
Adverse Effects
- Common adverse effects include nausea, constipation, sedation, and respiratory depression
- Approximately 6% of patients discontinue treatment due to intolerable adverse effects 3
- Consider prophylactic antiemetics 1
- Always prescribe laxatives to prevent constipation 4
Monitoring Parameters
- Respiratory rate
- Level of sedation
- Pain intensity using age-appropriate scale
- Presence of adverse effects
Cautions
- Use with caution in patients with renal impairment due to accumulation of morphine-6-glucuronide 1
- For patients with respiratory conditions, consider lower starting doses
- Naloxone should be available to reverse accidental overdose 4
Efficacy and Response
Research shows that standard doses of morphine during titration, as recommended by European Association for Palliative Care, are effective in clinical practice 2. Over 90% of patients achieve no worse than mild pain within a reasonably short time period when appropriate dosing is used 3.
The goal of morphine therapy should be to achieve adequate analgesia while minimizing adverse effects, with the endpoint being "no worse than mild pain" (≤30/100 mm on a visual analog scale) 3.