The aim of this study was to evaluate the local anesthetic effect of nisoxetine as infiltrative cutaneous analgesic. After rats were injected subcutaneously with nisoxetine, dose-response curves were constructed. The cutaneous anesthetic effect of nisoxetine or MK-801 (dizocilpine) was compared with lidocaine, a traditional local anesthetic. We found that nisoxetine and MK-801 acted like lidocaine and elicited dose-related cutaneous (local) anesthesia. The relative potency was nisoxetine > MK-801 > lidocaine (P<0.01) as infiltrative anesthesia of skin. On an equianesthetic doses (20% effective dose [ED 20], ED 50, and ED 80), nisoxetine produced longer action of cutaneous anesthesia than that of lidocaine or MK-801 (P < 0.01). Coadministration of nisoxetine or lidocaine with MK-801 showed an additive cutaneous anesthesia. Neither local injection of a large dose of nisoxetine, MK-801 nor lidocaine in the thigh area produced cutaneous anesthesia (data not shown). In conclusion, nisoxetine had a local anesthetic effect as infiltrative cutaneous analgesia with durations of actions longer than that of lidocaine or MK-801. That N-methyl-d-aspartate receptors may not contribute to the cutaneous (local) anesthetic effect of nisoxetine or lidocaine.
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