Articles: analgesics.
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Pharmacol. Biochem. Behav. · Jan 1987
Determination of cross tolerance in rat spinal cord using intrathecal infusion via sequential mini-osmotic pumps.
Continuous intrathecal (IT) infusion via ALZET mini-osmotic pumps was used to induced spinal tolerance to morphine in the rat. Naloxone (1 mg/kg IP), injected on day 3 of continuous IT morphine (10 micrograms/hr), produced mild withdrawal symptoms in all morphine-treated animals. In rats pretreated with continuous IT morphine (10 micrograms/hr) or saline, systemic morphine (2, 4, 8, 10 and 15 mg/kg IP) produced equivalent, dose-dependent antinociception using the tail-flick and paw pressure tests. ⋯ A sequential, double mini-osmotic pump technique for cross tolerance studies in rat spinal cord is described. In rats pretreated with continuous IT norepinephrine for 4 days, the antinociceptive actions of continuous IT morphine were reduced but not significantly different from saline-pretreated animals. These data suggest that morphine, injected into the spinal cord, does not produce behavioural analgesia by activation of local adrenergic systems.
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During a period of one year, 119 patients with chronic pain received injections of opioids via a catheter inserted in the lumbar epidural space. Twenty-three patients (19%) showed evidence of tolerance and were given droperidol 1.25-5.0 mg epidurally. ⋯ One patient given an accidental overdose of droperidol developed reversible Parkinsonism. It is concluded that epidural administration of the dopamine antagonist droperidol may be beneficial as supplementary medication to epidural opioids when tolerance develops.