Effect of diazepam and desmethyldiazepam in spasticity and rigidity

Abstract

Benzodiazepines reduce increased muscle stretch reflexes. To investigate the relationship between the necessary plasma concentrations of diazepam and its major metabolite desmethyldiazepam and the phasic and tonic ankle reflex activity on the other, 10 mg diazepam was given i.v. to 9 patients, 7 with spasticity due to multiple sclerosis and 2 with parkinsonian rigidity. Diazepam and desmethyldiazepam both had a normalizing effect on the increased phasic ankle reflex seen in spasticity. No effect was observed on the increased tonic reflexes in rigidity. The concentrations of diazepam necessary to reduce spasticity ranged between 300-2200 mg/l and were so high that drowsiness occurred. Desmethyldiazepam has a higher potency and a more long lasting effect on the increased phasic reflexes than diazepam.