Drugs
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Small spinal (intrathecal or extrathecal) doses of opioids induce a long-lasting and regional analgesic effect in various experimental animal models. Nowadays extrathecal morphine administration is considered an established method of controlling postoperative and cancer-induced pain conditions. The potency of morphine applied by the spinal route is higher than when the drug is applied by the intravenous (IV) route. ⋯ There are risks in replacing opioid administration by the oral or IV route with spinal opioids. Morphine should only be used in selected cases until the advantage of spinal opioid analgesia to control postoperative and cancer pain has been clearly defined in well-designed clinical studies. Spinal morphine dosages must be individualised according to the intensity of the nociceptive stimuli and should take into account intra-individual variability in drug responses due to pharmacokinetic and pharmacodynamic factors.