The pharmacology of 5-chloro-4-(2-imidazolin-2-yl-amino)-2,1,3-benzothiadiazole (DS 103-282), a novel myotonolytic agent.

5-Chloro-4-(2-imidazolin-2-yl-amino)-2,1,3-benzothiadiazole (DS 103-282) is a centrally acting agent with a novel chemical structure and a pharmacological profile different from that of myotonolytic drugs in current use such as diazepam, baclofen and dantrolene. It inhibits alpha- and gamma-rigidity in rats, reflex muscle tone in rabbits and the linguomandibular reflex in cats at low doses, but has little or no effect on gross spinal reflexes or electrically-induced segmental reflexes in cats. The mechanism underlying the muscle relaxation is unknown. Effects on convulsions induced by impaired GABA-transmission and by strychnine suggest a possible influence on glycine-mediated neurotransmission. In muscle-relaxing doses, DS 103-282 is without appreciable sedative, haemodynamic or neurochemical effects. Clinical investigations have confirmed the pharmacological predictions with regard to both the myotonolytic activity and the low propensity to produce side-effects.