Impact of famotidine on blood carnitine levels and L-carnitine supplementation dose in tube-fed patients with severe motor and intellectual disabilities.

<i>Introduction:</i> Carnitine is essential for mitochondrial fatty acid transport and energy production. Tube-fed patients with severe motor and intellectual disabilities (SMID) receiving carnitine-free enteral nutrition are at increased risk of carnitine deficiency. Famotidine, used to treat gastroesophageal reflux disease (GERD), inhibits carnitine transport <i>in vitro</i>, but its clinical impact remains unclear. This study investigated the effect of famotidine on blood carnitine concentrations and L-carnitine supplementation requirements in tube-fed patients with SMID. <i>Methods:</i> A retrospective observational study including patients receiving exclusive enteral nutrition and L-carnitine supplementation was conducted at the Tokyo Metropolitan Tobu Medical Center. Blood carnitine level and L-carnitine dose were compared between famotidine users and non-users. <i>Results:</i> Among 25 subjects (45 data points), famotidine users required significantly higher L-carnitine doses to maintain normal free carnitine levels than did non-users (22.0 ± 4.0 mg/kg/day vs. 13.0 ± 2.8 mg/kg/day, respectively [p = 0.024]). A correlation between L-carnitine dose and free carnitine level was observed only among non-users of famotidine (correlation coefficient: 0.352). Additionally, 36.8% of famotidine users exhibited persistently low free carnitine levels despite supplementation, compared to 3.9% of non-users. <i>Conclusion:</i> Famotidine use was associated with increased L-carnitine supplementation requirements, likely due to impaired renal carnitine reabsorption. Routine monitoring of famotidine-treated patients may help prevent L-carnitine deficiency. Further studies should assess possible long-term effects and explore alternative GERD treatments that have minimal impact on carnitine metabolism. Expanding insurance coverage for carnitine testing could improve early detection and intervention.