Antipsychotics, especially second-generation antipsychotics (SGAs), have been proven effective for treating psychosis as well as mood disorders.1,2 Because antipsychotics can lower the epileptogenic threshold, seizures are a serious potential adverse effect. Antipsychotics can cause isolated EEG abnormalities in 7% of patients with no history of epilepsy, and clinical seizures in .5% to 1.2% of such patients.3 Additionally, the neuropathophysiology underlying epilepsy can predispose patients to psychiatric disorders4; the estimated prevalence of psychosis in patients with epilepsy is approximately 7%.5 This review will shed light on the risk of clinical seizures related to antipsychotics.
Comparing seizure risk among antipsychotics
In a review of the World Health Organization’s adverse drug reactions database, Kumlien and Lundberg6 calculated the ratio of the number of reports of seizures to the total number of reports for each drug. They found that approximately 9% of all adverse drug reaction reports involving clozapine were due to seizures. Equivalent ratios were 5.90% for quetiapine, 4.91% for olanzapine, 3.68% for risperidone, 3.27% for haloperidol, and 2.59% for aripiprazole. Using the database of the Pharmacovigilance Unit of the Basque Country, Lertxundi et al7 reported a 3.2-fold increased risk of seizure with SGAs in comparison with first-generation antipsychotics (FGAs) (95% confidence interval [CI], 2.21 to 4.63), which went down to 2.08 (CI, 1.39 to 3.12) once clozapine was excluded. However, as the authors of both studies noted, the quality and relevance of this data are limited because it relies on spontaneous reporting.
Overall, the evidence regarding the seizure risk associated with antipsychotics is scarce. To the best of our knowledge, only 2 large observational studies have compared the seizure risks associated with different antipsychotics.
Using data from the UK-based Clinical Practice Research Datalink between 1998 and 2013, Bloechlinger et al8 examined the incidence rates of seizures among patients newly diagnosed with schizophrenia, affective disorders, or dementia who were prescribed antipsychotics. They excluded patients with a history of seizures or antiepileptic use. In the cohort of 60,121 patients, the incidence rates of seizures per 10,000 person-years were 11.7 (CI, 10.0 to 13.4) for those who did not use antipsychotics, 12.4 (CI, 10.9 to 13.8) for past users, 115.4 (CI, 50.1 to 180.7) for current users of haloperidol, 48.8 (CI, 30.7 to 66.9) for current users of quetiapine, 25.9 (CI, 11.8 to 40.0) for current users of risperidone, and 19.0 (CI, 8.7 to 29.3) for current users of olanzapine. No data were available about clozapine use.
In subsequent analyses, the authors found that among patients with affective disorders, only current use of medium- to high-potency FGAs (haloperidol, prochlorperazine, and trifluoperazine) was associated with a significantly increased risk of seizures (adjusted odds ratio: 2.51, CI, 1.51 to 4.18) compared with non-users.8 Among patients with dementia, current use of olanzapine or quetiapine and current use of any FGAs were associated with significantly increased odds of seizures. This study suggests that the underlying mental illness might modulate the seizure risk associated with antipsychotics.8
Wu et al9 conducted a study based on the National Health Insurance Research Database in Taiwan. They examined the 1-year incidence of new-onset seizures among patients diagnosed with schizophrenia or mood disorders who were new to antipsychotic treatment, and calculated the risk of seizure associated with each antipsychotic in reference to risperidone. They found that those receiving clozapine, thioridazine, and haloperidol were 2 to 3 times more likely to develop seizures than those treated with risperidone; risks associated with the rest of the FGAs were similar to that of risperidone.
The results of these 2 large cohort studies are somewhat concurrent in indicating that, other than clozapine, SGAs incur similar risks of seizures; furthermore, they specify that, contrary to earlier studies,10 haloperidol is associated with significantly higher odds of seizures. While both of these cohort studies controlled for several sociodemographic and clinical confounders, they have several limitations. First, diagnoses of seizures were based on information available in databases, which might be subject to inaccuracies. Second, neither study evaluated the effect of drug dosage and duration of exposure on new-onset seizures.
Continue to: Most evidence is from case reports