Abstract
Dantrolene and theophylline have in common pronounced actions on several muscular systems. Therefore we investigated the interaction of these 2 drugs in rats. Normal cases of dantrolene (4 or 2 mg/kg) caused an increase in the lethality produced by theophylline, but without showing the expected seizures of theophylline toxicity. This may be caused by a synergistic action on the heart or blood vessels. On the other hand, a small dose of dantrolene decreased theophylline-induced seizures and death. This may be due to the effect of dantrolene on calcium release in skeletal muscles. The dosage of dantrolene should be decreased when used with theophylline.