Effect of dantrolene sodium on muscle contraction

The force of contraction of the adductor pollicis before and after dantrolene sodium was evaluated in 5 paraplegic patients. The muscle was indirectly stimulated through supramaximal stimulation of the ulnar nerve at the wrist, with single pulse and variable number of stimuli at frequency of 50 Hz. There was a marked and significant reduction (an average of 64%) of the single twitch response in all patients while on medication. When the muscle, however, was stimulated with tetanic frequency no significant difference was evident in the force of the sustained contraction with or without medication. The amplitude of evoked electrical potentials, simultaneously recorded from the adductor pollicis remained unchanged irrespective of the status of medication. Decrement of the twitch response, with no effect on the electrical activity, tends to substantiate the distal effects of dantrolene on muscle contraction. The drug, however, does not seem to prevent the muscle from achieving its normal maximal tetanic force when activated with frequencies close to the physiological frequencies of maximal, voluntary effort (50 Hz.) These effects point to the usefulness and limitations of the drug in clinical situations.