Eliglustat-d is intended for use as an internal standard for the quantification of eliglustat by GC- or LC-MS. Eliglustat is an inhibitor of glucosylceramide synthase (IC = 40 nM for inhibition of glucosylceramide production in K562 cells). It is selective for glucosylceramide synthase over α-glucosidase I and II, α-1,6-glucosidase, lysosomal glucocerebrosidase, non-lysosomal glucosylceramidase, sucrase, and maltase (ICs = >10 µM for all). It decreases cell surface levels of the gangliosides GM and GM in K562 and B16/F10 cells with IC values of 24 and 29 nM, respectively. Eliglustat (150 mg/kg per day) decreases glucosylceramide levels in the liver and lungs of D409V/null mice, a model of Gaucher disease. Formulations containing eliglustat have been used in the treatment of type 1 Gaucher disease.