A 52-year-old Caucasian woman comes to the office for a routine follow-up visit. She complains of weakness and fatigue for the past two weeks. She 'feels tired' even while doing minor household chores. She denies fever or any changes in appetite or weight. Three months ago, she underwent surgery for carcinoma of the breast and has been on chemotherapy ever since. She is a retired nurse and lives at home with her husband. She was diagnosed with hypertension twenty years ago. Her current therapy includes cyclophosphamide, methotrexate, 5-flurouracil, ondansetron, atenolol and famotidine. Her vital signs are within normal limits. Examination is unremarkable, except for moderate pallor. Rectal examination shows no abnormalities. Her lab results reveal the following: The stool test for occult blood is negative. Which of the following is most likely responsible for her condition?

Question

A 52-year-old Caucasian woman comes to the office for a routine follow-up visit.  She complains of weakness and fatigue for the past two weeks.  She 'feels tired' even while doing minor household chores.  She denies fever or any changes in appetite or weight.  Three months ago, she underwent surgery for carcinoma of the breast and has been on chemotherapy ever since.  She is a retired nurse and lives at home with her husband.  She was diagnosed with hypertension twenty years ago.  Her current therapy includes cyclophosphamide, methotrexate, 5-flurouracil, ondansetron, atenolol and famotidine.  Her vital signs are within normal limits.  Examination is unremarkable, except for moderate pallor.  Rectal examination shows no abnormalities.  Her lab results reveal the following:    The stool test for occult blood is negative.  Which of the following is most likely responsible for her condition?

Quizplus · Accepted Answer

Explanation: This patient's laboratory results reveal a macrocytic anemia. Of all the drugs that she is currently taking, methotrexate is the drug that most commonly results in a macrocytic anemia. This side effect is attributed to the fact that methotrexate inhibits the enzyme dihydrofolate reductase (DHFR), which is essential for the conversion of folic acid to its reduced form (FH4- folinic acid), which can be utilized by the cells. The resulting folate deficiency then leads to the macrocytic anemia. Educational Objective: Trimethoprim, methotrexate, and phenytoin can interfere with folate metabolism and result in folic acid deficiency anemia.

A 52-Year-Old Caucasian Woman Comes to the Office for a Routine