MORPHINE: ACTIONS, DOSE
Morphine acts on the opioid receptors in the brain and spinal cord to produce analgesia. The perception of pain is altered both by a direct effect on the spinal cord, modulating peripheral nociceptive input, and by activation of the descending inhibitory systems from the brain stem and basal ganglia. Opioids also act on the limbic system and on higher centres to modify the emotional response to pain.
The systemic effects, including those affecting the gastrointestinal and respiratory tracts, are partly centrally mediated via the autonomic nervous system and partly due to a direct effect of the drug.
Dose-Morphine has a remarkably wide therapeutic range, producing analgesia in a
dose-dependent manner over a wide range of doses and there appears to be no ceiling effect to the analgesia; the useful dose is limited by adverse side effects.
There is no standard dose of morphine for the treatment of chronic cancer-related pain.
The dose required will depend on the severity of the pain, the type of pain, individual pharmacokinetic variations, the development of tolerance as well as the psychosocial issues which affect the perception of pain.

• The correct dose of morphine is that which controls the pain whilst causing tolerable side effects.
• The dose must be titrated for each individual patient

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