Dose of thiopental, pentobarbital, and phenytoin for maximal therapeutic effects in cerebral ischemic anoxia.

Recent interest in pharmacotherapy for various cerebral insults with potentially dangerous drugs, such as barbiturate anesthetics, has created a need to determine the lowest or optimal dose resulting in maximal therapeutic effects. Our earlier studies suggested that whole brain free fatty acid (FFA) accumulation during complete global ischemia reflects the evolution of brain damage. Various drugs effective in ameliorating ischemic brain injury were also effective in attenuating FFA accumulation. The degree of attenuation by a given drug at various doses may indicate the optimal dose. We studied the attenuation of whole brain FFAs (i.e., 20:4, 18:0, 18:1, and 16:0) by 15-120 mg/kg of thiopental or pentobarbital, or 50-300 mg/kg of phenytoin or ketamine intraperitoneal (IP), during 10-min decapitation ischemia in rats. Plasma and brain drug levels were measured except ketamine. Maximal attenuation of FFAs occurred at pentobarbital, thiopental, and phenytoin doses of 15, 30, and 150 mg/kg IP reducing total FFA by 18, 22, and 31%, respectively. These results indicate that maximal therapeutic effects are obtained at subanesthetic doses of barbiturates and at the anticonvulsant dose of phenytoin.