To characterise the impact of bariatric surgery for weight loss on anti-seizure drug (ASD) levels and seizure frequency in patients with a history of epilepsy or prior seizures.

Bariatric surgery is an increasingly utilised procedure amongst patients with obesity-related medical complications. The impact of bariatric surgery on seizure frequency and ASD levels are not well described.

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.

Forty-six patients with a history of seizures were identified (38 female), median follow up was 60 months [range 12-220 months]. Forty-four patients had recurrent and unprovoked seizures, 2 had a prior single seizure. Thirty-three patients were prescribed ASD at the time of bariatric surgery (median 1 [range, 1-3]).

Roux-en-Y procedure was performed in 40 patients, and sleeve gastrectomy in 6 patients. The median age at surgery was 44 years (range, 19-68). 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)

Five patients suffered a seizure within 6 months of bariatric surgery. Nine patients had increased seizures frequency following bariatric surgery. Sub-therapeutic ASD concentrations post-surgery were identified on 5/18 occasions (14 patients ). ASD doses were increased due to increased seizures frequency in 4 patients 3 who also had sub-therapeutic ASD concentrations. Five patients developed ASD associated side-effects. ASD doses were reduced within 6 months following bariatric surgery in 4 patients;  including 3 with ASD side-effects.