Answer
The Dextro and Levo of ephedrine and pseudoephedrine.
Work Step by Step
The Erythro configuration which is ephedrine is where the two groups on the chiral carbons in the same direction either right which is the dextro or left which is the levo.
The Threo configuration which is pseudoephedrine has the two groups of the chiral carbons in different directions and classified according to the methylamino group that have the higher priority to dextro and levo.
