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Relationship between plasma concentration of morphine and analgesic effectiveness
N Yokokawa1, K Hiraga, T Oguma
1National Cancer Centre, Tokyo, Japan.
Postgraduate Medical Journal
|January 1, 1991
Summary
Plasma morphine concentration varies widely, making it difficult to determine effective pain control levels. However, increasing morphine dosage and switching to continuous drip infusion can improve pain relief in cancer patients.
Area of Science:
- Pharmacology
- Oncology
- Pain Management
Background:
- Morphine is a vital analgesic for managing cancer pain.
- Understanding plasma morphine concentration is crucial for optimizing treatment.
Observation:
- Plasma morphine levels showed significant variability among patients with controlled pain at constant doses.
- Oral morphine bioavailability was reduced in patients with gastrointestinal issues or intestinal blockages.
- Fluid accumulation (pleural effusion, ascites, edema) significantly reduced plasma morphine levels.
Findings:
- Morphine plasma concentration increased with dose escalation for oral MS Contin, correlating with improved analgesia.
- Continuous morphine infusion led to higher plasma concentrations and effective pain relief in patients with poor oral absorption.
- Fluid accumulation, such as pleural effusion and ascites, approximately halved plasma morphine levels.
Implications:
- Individualized morphine dosing is necessary due to wide pharmacokinetic variability.
- Continuous infusion may be superior to oral administration in certain patient populations.
- Accurate and rapid measurement of plasma morphine is crucial for effective pain management and dose adjustment.