Nortriptyline is metabolized by cytochrome P450 2D6. Which statement regarding homozygotes for inactive alleles of cytochrome P450 2D6 is most accurate?
A. Homozygotes for inactive alleles of cytochrome P450 2D6 are not possible.
B. They require a higher dose of nortriptyline to achieve the same concentration seen in heterozygotes.
C. They have lower nortriptyline levels in the blood than patients with 2 active genes.
D. They require a higher dose of nortriptyline to achieve the same concentration seen in patients with 2 active genes.