A clinical and experimental investigation of the effects of tizanidine in trigeminal neuralgia.

Experiments in cats anesthetized with alpha-chloralose showed that tizanidine (TZD: 5-chloro-4-(2-imidazolin-2-yl-amino)-2,1,3-benzothiodiazole) partly resembled carbamazepine (CBZ) and baclofen (BCF) in that it depressed excitatory transmission and facilitated segmental inhibition of neurons in the spinal trigeminal nucleus oralis which responded to tapping but did not affect the response of neurons which responded to light stroking of the skin or bending the whiskers. In a double-blind crossover study of TZD in refractory trigeminal neuralgia, 8 of 10 patients had fewer painful paroxysms while on TZD. However, the 6 patients who elected to continue taking TZD experienced a recurrence of their attacks of trigeminal neuralgia within 1-3 months. The limited efficacy of TZD in the treatment of trigeminal neuralgia may be related to the fact that it has no effect on neuronal responses to low-threshold mechanoceptive stimuli, suggesting that low-threshold mechanoceptive neurons play an important role in the pathogenesis of trigeminal neuralgia.