Tachyphylaxis to local anesthetics has shown to be promote longer interanalgesic intervals between injections. Previous study demonstrated thermal hyperalgesia accelerates development of tachyphylaxis to sciatic nerve blockade in rats, while MK-801 prevents development of tachyphylaxis. Dextromethorphan is one of NMDA receptor antagonist similar to MK-801. A hypothesis that dextromethorphan would prevent the development of tachyphylaxis was tested in this study. A catheter was surgically implanted along the sciatic nerve a in rat. After recovery from surgery, the animal received repeated injections of 3% 2-chloroprocaine followed by motor block testing with or without hot-plate testing at $56^{circ}C$. In other experiments, dextromethorphan was administrered by intraperiotneal injection prior to an injection of local anesthetic therough the implanted catheter. Sensory and motor testing was then carried out. Rats injected with 2-chloroprocaine and subjected to hot-plate testing, developed tachyphylaxis to motor and sensory blockade. However, animals pretreated with dextromethorphan did not develop tachyphylaxis over series of three injections. Dextromethorphan seems to prevent development of tachyphylaxis to sciatic nerve blockade in this rat model. Dextromethorphan, one of N-Methyl-D-aspartate receptor antagonist, can be applied to prolong the effect of local anesthetic.