Dantrolene sodium for treatment of heatstroke victims: lack of efficacy in a canine model.

Dantrolene sodium, a skeletal-muscle relaxant known to be effective for treatment of malignant hyperthermia, was evaluated for efficacy in treatment of heatstroke. Non-exertional heatstroke was induced in 11 dogs by external heating following barbiturate anesthesia. When core temperature reached 43 degrees C (109.4 degrees F) heating was discontinued and control animals (n = 6) were allowed to cool passively in room air. Treatment animals (n = 5) received 5 mg/kg dantrolene sodium intravenously at the start of room-air cooling. Serial temperatures (pulmonary arterial, rectal, cerebral, and subcutaneous), blood chemistry tests (including electrolytes, liver enzymes, and complete blood count), and hemodynamic parameters (including cardiac output, arterial pressure, and urinary output) were followed for 12 hours after induction of heatstroke. Autopsies, including gross and microscopic examination, were performed on all animals. Dantrolene administration did not significantly affect cooling rates, hemodynamic parameters, pathological changes, or clinical outcome. Statistically significant changes in urinary output and serum creatinine observed in the first hours after dantrolene administration can be attributed to the mannitol vehicle in which the drug was delivered. There were no statistically significant differences in these values at 12 hours. Dantrolene sodium does not appear to enhance passive cooling in treatment of non-exertional canine heatstroke.