In elderly patients with depression, which of the following best describes the relationship between CYP2D6 phenotype and O-desmethylvenlafaxine (ODV) levels?
A. Normal metabolizers had lower ODV levels than poor metabolizers
B. All metabolizer groups had similar ODV levels
C. Intermediate metabolizers had the highest ODV levels
D. Poor metabolizers had higher ODV levels than normal metabolizers
E. Ultra-rapid metabolizers had lower ODV levels than normal metabolizers