The effect of weight reduction surgery on the efficacy and tolerability of epilepsy pharmacotherapy

Background: Bariatric surgery is an increasingly utilized procedure among patients with obesity-related medical complications. The impact of bariatric surgery on seizure frequency and antiseizure drug (ASD) levels are not well described. Methods: We conducted a retrospective chart review of adult patients with a history of epilepsy or seizures undergoing bariatric surgery for morbid obesity from September 1997–September 2019. The median follow-up was 60 months [range 9–220 months]. Results: Forty-six patients with a history of seizures were identified (38 female); 44 patients had recurrent and unprovoked seizures. Seventeen sets of pre- and post-surgery drug concentrations from 14 patients were reviewed. The median age at surgery was 44 years (range, 19–68). Thirty-three patients were prescribed ASDs at the time of bariatric surgery (median 1 drug [range, 1–3]). Laparoscopic Roux-en-Y was performed in 40 patients, and sleeve gastrectomy in 6 patients. Median pre-surgery weight was 120.75 kg (range, 71–230) and BMI 44.4 kg/m² (range, 34–77.6). Six months following surgery the median weight was 89.5 kg (range, 58.2–202) and BMI 34.2 kg/m² (range, 24.5–61.9). Nine patients (19.6%) had a worsening of seizure control on long-term follow-up (median 60, range 9–220 months) following bariatric surgery, including five (10.8%) who suffered seizures within 6 months of bariatric surgery. Five patients developed ASD-associated side effects following bariatric surgery including irritability in two patients (levetiracetam and phenytoin) and one patient each suffering from somnolence (phenytoin), hyperammonemic encephalopathy (sodium valproate), and nausea and vomiting (carbamazepine). Subtherapeutic post-surgery drug concentrations were identified in 5 patients and supratherapeutic concentrations in one patient. In the initial 6 months following surgery, ASD doses were increased in five patients and reduced in five. Conclusions: The majority of patients with epilepsy who undergo bariatric surgery have no change in seizure frequency. However, a significant minority of patients may experience medication side effects or an increase in seizure tendency due to the impact of bariatric surgery on ASD drug absorption and metabolism leading. Pre- and post-surgical serum concentrations should be measured in patients with seizures or epilepsy receiving ASDs.