PHARMACOKINETICS AND ANALGESIC EFFECT OF SLOW-RELEASE ORAL MORPHINE SULPHATE IN VOLUNTEERS

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Abstract
Sustained-release oral morphine sulfate (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 ischemic forearm pain test increased to a maximum .apprx. 40 min after the calculated peak plasma concentration of morphine had been achieved, and remained greater than control values as plasma morphine concentration decayed. 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%.