Therapeutic time window and dose response of the beneficial effects of ketamine in experimental head injury

Background and Purpose The aim of this study was to determine the time and dose response of the therapeutic effects of the Af-methyl-D-aspartate receptor antagonist ketamine in experimental head injury. Methods Sixty-six male Sprague-Dawley rats were divided into eight groups. Groups A, B, and C were surgically prepared but received no trauma. Groups D through H received a nonpenetrating impact to the left cranium. Group A (n = 7) received no treatment. Groups B (n = 4) and C (n = 5) received 60 and 120 mg/kg IP ketamine, respectively. Group D (n=8) received no treatment. Groups E (n=8) and F (n = 7) received 120 and 180 mg/kg IP ketamine, respectively, 1 hour after head trauma. Groups G (n=7) and H (n=9) were treated with 180 mg/kg IP ketamine 2 and 4 hours after head trauma, respectively. Neurological severity score (NSS, 0 through 25 from no injury to severe injury) was determined at 1, 24, and 48 hours after head trauma. After death at 48 hours, cortical slices were taken adjacent to the lesion on the traumatized hemisphere and from comparable sites in the contralateral hemisphere for determination of tissue specific gravity and water content. Brains were then placed in 4% formaldehyde, and the volume of hemorrhagic necrosis was measured 4 days later. NSS was compared within and between groups using the Kruskal-Wallis test for repeated measurements and Mann-Whitney U test for post hoc testing. Water content, specific gravity, and hemorrhagic necrosis were compared within and between groups using two-way ANOVA followed by Fisher's protected least significant difference procedure. A value of P<.05 was considered statistically significant. Results Head trauma alone increased NSS, decreased specific gravity, increased water content, and caused cerebral infarction in the injured hemisphere. Ketamine given in two time-dose regimens, 180 mg/kg IP at 2 hours (group G) and 120 mg/kg IP at 1 hour (group F) after trauma, improved NSS from 11.6±1.7 and 14.4±0.8 at 1 hour to4.4±1.3 and 8.0±1.4 (mean±SEM) at 48 hours, respectively (P<.03). Compared with the untreated group (group D), 180 mg/kg IP ketamine given at 2 and 4 hours after head trauma decreased the volume of hemorrhagic necrosis from 37.1 ± 9.5 mm3 to 10.1 ± 3.8 and 15.3±3.6 mm3, respectively (P<.05). Brain tissue specific gravity and water content at 48 hours were not significantly different between treated and untreated groups. There was no difference in rectal and temporalis muscle temperature between groups. Conclusions We conclude that 180 mg/kg IP ketamine was effective in ameliorating neurological dysfunction after head trauma in rats when the administration time was delayed for 1 hour to 2 hours but not after 4 hours. When given at 1 hour after head trauma, ketamine at 120 mg/kg but not 60 mg/kg is effective in reducing neurological damage after head trauma.