(+)-D-threo-PDMP is a ceramide analog and is one of the four possible stereoisomers of PDMP . (+)-D-threo-PDMP is an inhibitor of glucosylceramide synthase. It inhibits glucosylceramide synthase by 50% when used at a concentration of 5 μM in an enzyme assay. (+)-D-threo-PDMP is the active component of racemic DL-threo-PDMP . In vitro, (+)-D-threo-PDMP inhibits the synthesis of glucosylceramide synthase and lactosylceramide in B16 melanoma cells when used at a concentration of 25 µM and inhibits cell binding to laminin and collagen when used at concentrations of 10 and 25 µM. It also inhibits β-1,4-galactosyltransferase 6 (B4GALT6) and prevents lactosylceramide synthesis, which is a promotor of neuroinflammation in mice during chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. (+)-D-threo-PDMP inhibits ganglioside biosynthesis, reduces long-term potentiation (LTP) in mouse hippocampal CA1 neurons, and impairs learning in the four-pellet taking test in mice.