Effective against partial and generalised tonic-clonic seizures. Status epilepticus. Blood testing is essential when using phenytoin as the relationship between dose and blood level is complex. Possible side effects: Skin rash if allergic to phenytoin. Unsteadiness, drowsiness and slurred speech may occur if too high a dose is used. Coarsening of facial features, overgrowth of gums, acne and growth of excess hair may be problems with prolonged therapy, as can some anaemias (treated with folic acid). Unsteady gait, shaky movements, sedation and rapid involuntary movement of the eye.