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

Introduction: 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 in vitro, 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. Methods: 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. Results: 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. Conclusion: 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.