Psychiatric comorbidity in patients with epilepsy: a population-based study

Patients with epilepsy often suffer from concomitant psychiatric disorders. Treatment patterns and the extent of comorbidity are insufficiently investigated and appropriate methods are scarce. The purpose of the study was to estimate the prevalence of psychiatric comorbidity in patients with epilepsy and to investigate prescription patterns of drugs prescribed for psychiatric disorders in epilepsy. Prescription data from the Norwegian Prescription Database (NorPD) regarding the use of CNS-active drugs included anonymous data from almost 190,000 patients and 1.1-1.3 million prescriptions per year (2004-2007). Searches were based upon use of specific drugs, defined daily doses, number of patients, prescriptions, gender, and age. Reimbursement codes related to psychiatric diagnosis were used as indicators for clinical use. The prevalence of psychiatric comorbidity in patients with epilepsy was estimated to be 32%. There were 56% women and 44% men participating in the study. Among patients using antidepressants two thirds were women, but no gender differences were seen with antipsychotic medication. Antidepressants and antipsychotics were used 3.4 (20.9%) and 5.8 (13.4%) times more frequently than in the general population, accounting for 7.88 and 1.99 defined daily doses (DDDs)/1,000 inhabitants/day/year respectively. Lamotrigine was the most commonly used antiepileptic drug (AED) in epilepsy, accounting for 33% of the use of AEDs (in total 5.65 DDDs/1,000 inhabitants/day/year). The use of benzodiazepines was 9.55 DDDs/1,000 inhabitants/day/year. The patients had complex pharmacotherapy with two to eight concomitant drugs. The present study gives an estimate of psychiatric comorbidity of 32% in patients with epilepsy in a nation-wide population. The pharmacotherapy in this patient population is complex. The results provide valuable data on prescription patterns that contribute to pharmacovigilance on a national scale.