Final answer:
Hydroxychloroquine (Plaquenil) is not classified as an antimetabolite, unlike the other medications listed, which interfere with DNA synthesis by acting as nucleotide analogs or inhibitors.
Step-by-step explanation:
Among the choices provided, all the following medications are considered antimetabolites except hydroxychloroquine (Plaquenil).
- Fluorouracil (Efusex) is a pyrimidine antimetabolite that inhibits the synthesis of 2-deoxythymidine, affecting DNA production.
- 6-Mercaptopurine (6-MP) is a purine analog that inhibits adenine nucleotide biosynthesis, essential for DNA synthesis.
- Gemcitabine (Gemzar®) is similar to fluorouracil and works through a mechanism that interferes with DNA synthesis.
- Hydroxychloroquine (Plaquenil), on the other hand, is not an antimetabolite but rather has a variety of uses including the treatment of malaria and certain autoimmune diseases, and does not act through interference with nucleotide synthesis.
Therefore, the medication not classified as an antimetabolite is hydroxychloroquine (Plaquenil).