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Pharmacokinetics and analgesic effect of slow-release oral morphine sulphate in volunteers
Abstract:
Sustained-release oral morphine sulphate (MST) 20 mg was administered to 11 healthy volunteers. Mean peak plasma morphine concentration was 14.8 ng ml-1, and occurred at a mean time of 142.5 min after ingestion. Analgesia assessed by an ischaemic forearm pain test increased to a maximum approximately 40 min after the calculated peak plasma concentration of morphine had been achieved, and remained greater than control values as plasma morphine concentration decayed. However, there was not a significant correlation between analgesia and plasma morphine concentration. This may result from delay in brain penetration by morphine. The mean systemic availability of morphine in the first 7 h after administration of MST was 18.3%.
Insights
Sustained-release oral morphine sulphate (MST) provides pain relief, but its effectiveness doesn't directly correlate with blood levels. This suggests morphine's brain entry may be delayed, impacting immediate pain management outcomes.
Area of Science:
- Pharmacology
- Pain Management
- Clinical Pharmacology
Background:
- Sustained-release oral morphine sulphate (MST) is a common analgesic.
- Understanding the pharmacokinetic and pharmacodynamic relationship of MST is crucial for optimizing pain management.
Purpose of the Study:
- To evaluate the pharmacokinetic profile of sustained-release oral morphine sulphate (MST).
- To assess the pharmacodynamic effects of MST on pain relief in healthy volunteers.
- To investigate the correlation between plasma morphine concentration and analgesia.
Main Methods:
- Administration of 20 mg MST to 11 healthy volunteers.
- Measurement of plasma morphine concentrations over time.
- Assessment of analgesia using an ischaemic forearm pain test.
Main Results:
- Peak plasma morphine concentration reached 14.8 ng/mL at 142.5 minutes.
- Maximum analgesia occurred 40 minutes after peak plasma concentration.
- No significant correlation was found between plasma morphine levels and analgesia.
- Mean systemic availability of morphine was 18.3% within the first 7 hours.
Conclusions:
- Analgesia from MST may be delayed due to factors like brain penetration time.
- The relationship between plasma morphine concentration and pain relief is complex.
- Further research is needed to fully understand MST's central effects and optimize its clinical use.