Clinical Effects of Intravenously Administered Dantrolene

To compare side effects after intravenous administration of dantrolene sodium in subjects susceptible to and those nonsusceptible to malignant hyperthermia (MHS and MHN, respectively). We studied two groups, six patients thought to be MHS and six assumed MHN subjects, and analyzed their responses to intravenously administered dantrolene. Dantrolene (3 mg/kg) was administered slowly into an antecubital vein, and blood samples were withdrawn from the other arm at 5 and 25 minutes after infusion. Shortly thereafter, all subjects underwent a clinical neurologic assessment, and side effects were graded subjectively by the study participants. Side effects occurred in all subjects. Visual symptoms occurred more commonly in MHN than in MHS subjects. Subjective muscle weakness of the extremities, dizziness, and fatigue occurred more commonly and were more severe in MUS patients than in MHN subjects. In patients recovering from an episode of malignant hyperthermia for which dantrolene has been administered, these side effects should be considered. Although the presence of side effects does not outweigh the usefulness of this drug in treating malignant hyperthermia, it may be a consideration in deciding whether to administer dantrolene prophylactically before surgical procedures in known or suspected MHS patients.