A short note on Lidocaine therapeutic profile 

When the lidocaine dose is increased from 1 mg/kg to 1.5 mg/kg, the risk of CNS toxicity increases from 10% to 80%. 

Usually, seizures generally do not occur with lidocaine levels of less than 10 mcg/mL but other CNS effects may occur like lightheadedness, dizziness, visual disturbance, headache, numbness, impaired concentration, dysarthria, tinnitus, muscular twitching etc