Methotrexate (an older cancer treatment medication) can be used as first-line therapy for rheumatologic and psoriatic diseases. One of the side effects of methotrexate usage mimics which one of the following vitamin deficiencies?: (A) Pyridoxine (B6), (B) Biotin (B7), (C) Niacin (B2), (D) Folate (B9)
Answer is D. Methotrexate targets and inhibits FH2 reductase, which catalyzes the reduction of FH2 to FH4 . Thus, in the presence of methotrexate, FH4 cannot be regenerated, and the body becomes functionally folate deficient. Methotrexate does not interfere with the absorption or reactions of the other B vitamins listed as potential answers.