Carbamazepine‐ and oxcarbazepine‐induced hyponatremia in people with epilepsy

<jats:title>Summary</jats:title><jats:sec><jats:title>Objective</jats:title><jats:p>To ascertain possible determinants of carbamazepine (<jats:styled-content style="fixed-case">CBZ</jats:styled-content>)– and oxcarbazepine (<jats:styled-content style="fixed-case">OXC</jats:styled-content>)–induced hyponatremia in a large cohort of people with epilepsy.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We collected data on serum sodium levels in people with epilepsy who were attending a tertiary epilepsy center while on treatment with <jats:styled-content style="fixed-case">CBZ</jats:styled-content> or <jats:styled-content style="fixed-case">OXC</jats:styled-content>. We defined hyponatremia as Na+ ≤134 <jats:styled-content style="fixed-case">mE</jats:styled-content>q/L and severe hyponatremia as Na+ ≤128 <jats:styled-content style="fixed-case">mE</jats:styled-content>q/L.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>We identified 1,782 people who had used <jats:styled-content style="fixed-case">CBZ</jats:styled-content> (n = 1,424) or <jats:styled-content style="fixed-case">OXC</jats:styled-content> (n = 358), of whom 50 were treated with both drugs. Data on sodium level measurements were available in 1,132 on <jats:styled-content style="fixed-case">CBZ</jats:styled-content> and in 289 on <jats:styled-content style="fixed-case">OXC</jats:styled-content>. Hyponatremia occurred in 26% of those taking <jats:styled-content style="fixed-case">CBZ</jats:styled-content> and 46% of those taking <jats:styled-content style="fixed-case">OXC</jats:styled-content>. This was severe in 7% in the <jats:styled-content style="fixed-case">CBZ</jats:styled-content> group and 22% in the <jats:styled-content style="fixed-case">OXC</jats:styled-content> group. Hyponatremia was symptomatic in 48% and led to admissions in 3%. Age over 40 years, high serum levels of <jats:styled-content style="fixed-case">CBZ</jats:styled-content> and <jats:styled-content style="fixed-case">OXC</jats:styled-content>, and concomitant use of other antiepileptic drugs were the main risk factors for hyponatremia in both treatment groups. Female patients on <jats:styled-content style="fixed-case">OXC</jats:styled-content> were at a higher risk than male patients of hyponatremia. The risk of hyponatremia on <jats:styled-content style="fixed-case">CBZ</jats:styled-content> was significantly associated with the risk of hyponatremia on <jats:styled-content style="fixed-case">OXC</jats:styled-content> within a subgroup that used both drugs consecutively.</jats:p></jats:sec><jats:sec><jats:title>Significance</jats:title><jats:p>Hyponatremia is a common problem in people taking <jats:styled-content style="fixed-case">CBZ</jats:styled-content> or <jats:styled-content style="fixed-case">OXC</jats:styled-content>. Regular ascertainment of sodium levels in those taking either drug is recommended and results should be acted on.</jats:p></jats:sec>