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Folinic acid
40%
2/5
Folic acid
0%
0/5
Vitamin B12
60%
3/5
Ferrous sulfate
Thymidine
Select Answer to see Preferred Response
Folinic acid (leucovorin) is a reduced form of folic acid used to "rescue" patients from the macrocytic anemia caused by methotrexate. As the reduced form of folic acid, folinic acid more effectively circumvents the block on dihydrofolate reductase compared to folic acid itself. Folic acid may be used, but it is not as effective and it is not the most appropriate therapy in this case. Davenport reviews that "macrocytic anemias are classified as those resulting from disorders of DNA synthesis of erythrocyte precursors in bone marrow (megaloblastic anemias) or those caused primarily by alcoholism, liver disease and hypothyroidism (nonmegaloblastic anemias). A blood smear should be performed to differentiate the two forms." Shiroky et al. conducted a study of 92 patients comparing methotrexate alone to methotrexate plus leucovorin. They found that the "methotrexate-leucovorin protocol used significantly reduces common side effects of methotrexate therapy without significantly altering efficacy." Illustration A demonstrates the interaction of methotrexate and folinic acid in the process of purine biosynthesis. Incorrect Answers: Answer 2: Folinic acid (the reduced form of folic acid) more effectively circumvents the block on dihydrofolate reductase compared to folic acid itself. Answer 3: Methotrexate causes folic acid (not Vitamin B12) deficiency. Answer 4: Methotrexate causes folic acid (not iron) deficiency. Answer 5: Thymidine is used to treat an overdose of 5-fluorouracil (5-FU)
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