Dantrolene as a Treatment for Hyperthermia in Patients After Subarachnoidal Hemorrhage

Background:

Fever episodes occur in more than 50% of patients admitted to the ICU for subarachnoidal hemorrhage, central nervous system infection, seizure control, hemorrhagic stroke, and closed head injury despite antibiotic and antipyretic therapy.

The exact mechanism of hyperthermia-induced brain injury is not known; however, various processes may be involved. For example, hyperthermia might increase the release of excitatory neurotransmitter or trigger an abundant amount of oxygen free radicals. Hyperthermia may also aggravate blood-brain barrier disruption, impair cytoskeletal proteolysis, and/or enhance inhibition of enzymatic protein kinases, which, in turn, would impair recovery of energy metabolism. Antipyretics are effective for conventional fever, but less useful for various central hyperthermia syndromes, especially those resulting from strokes, SAH, and head injuries. Even aggressive cooling is usually insufficient in patients with fever because it is unable to overcome the high metabolic rate in these patients. Likewise, physical cooling is counteracted by the thermoregulatory defenses being activated to maintain hyperthermia. In non-sedated individuals, active cooling increases metabolic stress without decreasing core temperature at all. To date, treatment of centrally mediated hyperthermia remains unsatisfying.

Dantrolene has been available since 1975 as a specific treatment for acute malignant hyperthermia crises. However, dantrolene is increasingly being used for emergency treatment of life-threatening hyperthermia that is unresponsive to conventional treatments. For example, the drug has been used with some success for acute treatment of life-threatening hyperthermia resulting from neuroleptic malignant syndrome and hyperthermia associated with overdoses of various drugs. It has also been used for treatment of various other types of hyperthermia.

Efficacy in these cases appears to be based on a non-specific action of the drug; but to the extent dantrolene is effective, its action must conform to the laws of thermodynamics. Dantrolene must, therefore, reduce metabolic heat production, augment systemic heat loss, or alter the normal distribution of heat within the body. In other words, dantrolene must reverse the abnormal (or ineffective) thermoregulatory control that initiates the hyperthermic crises.