A case of acute dizziness and eye movement abnormality in the course of long-term treatment with antiepileptic drugs

A 42-years-old woman who had dizziness for the previous 10 days visited our hospital. She had experienced epileptic attacks and suffered from repeated seizures. She was under treatment with 4 antiepileptic drugs ( phenytoin, phenobarbital, valproate, and car-bamazepine). Horizontal gaze-evoked nystagmus was observed. Blood tests and imaging examinations showed no abnormal findings. The blood concentrations of these antiepileptic drugs were at their therapeutic dose. However, the concentration of phenytoin and phenobarbital blood concentrations were slightly high. Following adjustment of the drug dosage for epilepsy, her dizziness and abnormal eye movement improved. Antiepileptic drugs are usually known to cause drug-induced dizziness and eye movement abnormalities. The reduction of dosage or withdrawal of these drugs is often very ef-fective. However, certain patients show symptoms of drug toxicity for drugs at their therapeutic dose. Phenobarbital occasionally induces an increase in phenytoin’s toxicity. Al-though phenobarbital treatment is known to cause dizziness and nystagmus in children, very few reports indicate that phenobarbital causes similar symptoms in adults.