Vitamin D Levels and Bone Turnover in Epilepsy Patients Taking Carbamazepine or Oxcarbazepine

Authors


Address correspondence and reprint requests to Dr. S. Mintzer at 900 Walnut Street, Suite 200, Philadelphia, PA 19107, U.S.A. E-mail: scott.mintzer@jefferson.edu

Abstract

Summary: Purpose: Evidence suggests that enzyme-inducing antiepileptic drugs (AEDs) may decrease serum 25-hydroxyvitamin D (25-OHD) levels and increase bone turnover. We sought to determine whether these are affected by treatment with carbamazepine (CBZ) or oxcarbazepine (OXC).

Methods: We measured serum levels of 25-OHD, parathyroid hormone (PTH), osteocalcin (OCLN), bone alkaline phosphatase (BAP), and urinary N-telopeptides of type I collagen cross-links (NTX) in normal controls (n = 24) and in epilepsy patients taking CBZ (n = 21) or OXC (n = 24) in monotherapy. CBZ patients were subsequently switched overnight to OXC monotherapy, and after 6 weeks, the tests were repeated.

Results: 25-OHD levels were lower in each drug-treated group (OXC, 19.4 ± 2.3 pg/ml; CBZ, 20.4 ± 2.4) than in the controls (27.5 ± 2.8) (ANOVA, p = 0.052). This difference was significant for the OXC group (p < 0.05). PTH, BAP, and NTX did not differ significantly among groups. OCLN levels were somewhat elevated in the OXC group (2.79 ± 0.47 ng/ml) and more clearly and significantly elevated in the CBZ group (3.63 ± 0.36) compared with controls (2.38 ± 0.41) (p = 0.053). Because the data were very similar between OXC and CBZ groups, they were combined to increase statistical power. The combined drug-treatment group had significantly higher BAP (p = 0.02) and lower 25-OHD (p = 0.015) than did controls. The latter remained significant even after accounting for the confounding effects of age on 25-OHD levels (p < 0.05). No significant differences were found after CBZ patients were switched to OXC.

Conclusions: Epilepsy patients taking OXC or CBZ have significantly lower 25-OHD than do normal controls, with a pattern of changes in other bone biomarkers suggestive of secondary hyperparathyroidism. It may be prudent for patients taking CBZ or OXC to be prescribed 25-OHD replacement.

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