Effects of enzyme-inducing antiseizure medication on vitamin D dosing in adult veterans with epilepsy

Abstract

Background: The association of antiseizure medication (ASM) and bone density abnormalities has long been recognized; however, there remains a lack of consensus on efficacy and optimal vitamin D dosing in patients receiving enzyme inducing and non-inducing ASMs. The objective was to explore the relationship between ASMs and vitamin D supplementation requirements in a population of adult patients with epilepsy.

Methods: Patients with a diagnosis of epilepsy receiving supplemental vitamin D were included in this retrospective chart review. All instances of 25-hydroxyvitamin D₃ (25-OHD) measured among those patients were compared between patients taking an enzyme inducing antiseizure medication (EIASM) to patients receiving ASM regimens only containing non-enzyme inducing antiseizure medications (NIASM). ASM use, prescription and over the counter (OTC) vitamin D use, 25-OHD plasma concentration, presence of chronic kidney disease (CKD), age, gender, and ethnicity were collected. Multiple linear regression was used to adjust for potentially confounding variables; the model included a cluster by participant term to account for repeated patients in the dataset.

Results: There were 542 vitamin D levels evaluated from 172 unique patients. There was an 11.5 % higher absolute percent increase in patients who achieved a 25-OHD level over 30 ng/mL in the NIASM (p = 0.012). Patients on EIASMs were supplemented with an additional 508 units of vitamin D daily (95 %CI 136-878, p = 0.007). When adjusted for CKD, OTC vitamin D use, OTC multivitamin use, age, gender, and ethnicity, patients on EIASMs were supplemented with an additional 445 units of vitamin D (95 %CI -69 to 960, p = 0.089) compared to NIASM use.

Conclusions: Patients taking EIASMs had an increase in vitamin D deficiency and vitamin D supplementation suggesting that EIASMs impact vitamin D metabolism. Closer monitoring of vitamin D status in patients with epilepsy, especially those on EIASMs, is warranted. This evaluation suggests that for patients taking ASM, use of a lower dose OTC requires closer monitoring of vitamin D status in patients with epilepsy, especially those on EIASMs, is warranted. vitamin D agent may not be adequate.

Keywords: Antiseizure medication; Cholecalciferol; Drug interaction; Epilepsy; Ergocalciferol; Vitamin D.