Biol. Pharm. Bull. 30(9) 1763—1767 (2007)

and cardiac infarction leads to neuron dysfunction and cell death, and its after-effects such as dementia, perception injury and hemiplegia are serious problems. Excess glutamate released from the neuron, energy disorder from impaired circulation and free radical generation have been clarified as the causes leading to neuron death involved with cerebral ischemia. Busto et al. reported in 1989 that it was possible to prevent neuron dysfunction and cell death in the ischemia by lowering the body temperature of the rats, i.e. surface cooling to 32—33 °C. The multiple mechanisms of hypothermia-induced neuroprotection were identified such as reduction in cerebral metabolism, energy depletion and stabilization of cell membranes as reported previously. Hypothermia therapy has been increasingly applied to the humans since it was proved useful in rats and dogs to treat experimental ischemic brain injury in the early 1990s. On the other hand, hypothermia therapy possibly causes side effects such as arrhythmia, impaired immune function and coagulation disorders as reviewed by Schubert. In order to negate these side effects, several kinds of medicines such as antiarrhythmic drugs, antibiotics and anticoagulants are administered to the patients. Moreover, like other critically ill patients, those with severe head injuries typically receive a large number of medications. In addition, although combination pharmacotherapy with an inhibitor of glutamate and calcium might act synergistically by attenuating an ischemia-induced release of neurotoxic glutamate, it is possible for undesirable drug-interactions to occur. Although hypothermic patients tend to receive many different pharmacologic agents, most of them are administered according to dosing schedules derived from the normothermic host. These schedules do not take into consideration any changes in drug pharmacokinetics or pharmacodynamics associated with hypothermia therapy. Physiological and biochemical changes may happen during hypothermia therapy related to a reduction in blood flow and energy deficiency. Therefore, pharmacokinetics of a drug during hypothermia should differ largely from normothermic conditions. There have been a few reports that recently investigated the influence of hypothermia on drug pharmacokinetics and pharmacodynamics such as phenytoin, neostigmine and vecuronium. As well, the possibility of side effects and drug-interactions caused by variations in drug pharmacokinetics during hypothermia must be sufficiently understood. In the present study, we assessed systematically the influence of hypothermia at 32 °C on the pharmacokinetics of several compounds as models with different elimination processes. Moreover, we examined the pharmacokinetic change in hypothermia at 28 °C, aiming to consider the unexpected conditions such as too much cooling and body temperature dependency on pharmacokinetic change of a drug in the patients fully by three different body temperatures.