The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Dec 1990
An isobolographic analysis of the antinociceptive effect of systemically and intrathecally administered combinations of clonidine and opiates.
The antinociceptive interaction of opiate analgesics with clonidine was examined with the tail-flick and 55 degrees C hot plate tests. Male Sprague-Dawley rats received fixed ratios of clonidine to fentanyl, meperidine or morphine by i.v. and intrathecal injection. Data are expressed as percentage of maximal possible effect and the dose producing 50 percentage of maximal possible effect for each drug or drug combination is used to index potency. ⋯ This interaction may be additive or synergistic, depending on route of administration and the nociceptive test used. The timing of injections and pharmacokinetic factors may also influence the results. Moreover, these results suggest that the interaction between the opiate and alpha-2 adrenergic receptors occurs within the spinal cord.