[The effect of flupirtine, various analgesics and muscle relaxants on skeletal muscle tone in the conscious rat].

The influence of the skeletal muscle tone by flupirtine (D-9998, Katadolon; CAS 56995-20-1), some selected analgesics and muscle relaxants was investigated in conscious rats after intraperitoneal administration. Benzodiazepines (diazepam and tetrazepam), baclofen, dantrolene and mephenesine reduced the tone of the skeletal muscle. Opiate analgesics, such as morphine, codeine and tramadol, enhanced the muscle tone. Flupirtine reduced the skeletal muscle tone at doses comparable with its antinociceptive effective doses. In this dose range no sedative side effects as ataxia or decrease of spontaneous motor activity could be observed. The mode of this muscle relaxing effect of flupirtine is not known in all details. It is, however, likely that flupirtine is able to inhibit the mono- and/or polysynaptic reflexes at the spinal level.