Motor paralysis increases brain uptake of lidocaine during status epilepticus

The effect of pH on brain uptake of lidocaine during status epilepticus was studied by comparing blood and brain lidocaine concentrations and pH in paralyzed and nonparalyzed rats during pentylenetetrazol-induced status. Status produced both brain and blood acidosis; paralysis prevented the blood acidosis. Both brain and blood lidocaine concentrations were increased in the status animals. The increase in brain lidocaine was greatest (10-fold over control) in animals paralyzed during status. These findings probably reflect the fall in brain and blood pH during status affecting the partitioning of the weak base lidocaine (pKa 7.86). Paralysis prevents blood, but not brain, acidosis, thereby maximizing the pH gradient and partitioning of lidocaine into the brain.