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Chapter 19. Colorectal Cancer

GC is a 58-year-old man with a recent diagnosis of stage IV colon cancer. His prior medical history is significant for hypertension (on lisinopril and hydrochlorothiazide [HCTZ]), deep vein thrombosis (on warfarin), and atrial fibrillation (on amiodarone). The oncologist informs the patient the plan is for him to receive neoadjuvant chemotherapy followed by surgery. The oncologist informs GC that he will receive the chemotherapy regimen XELOX (capecitabine and oxaliplatin).

  • XELOX:

  • Capecitabine 1000 mg/m2 orally twice daily for 14 days

  • Oxaliplatin 130 mg/m2 IV on day 1

  • Repeat cycle every 3 weeks

GC presents to your pharmacy with a prescription for capecitabine. Which of his home medications has a significant drug interaction with his capecitabine?

a. Lisinopril

b. HCTZ

c. Warfarin

d. Cetirizine

Answer c is correct. Capecitabine has a black boxed warning for increased risk of bleeding in patients receiving warfarin therapy. This is thought to be due to an increase in S-warfarin. R-warfarin levels are not affected. Consideration should be given to switching anticoagulants in patients who are to receive warfarin. In patients receiving concomitant capecitabine and warfarin, strict monitoring of prothrombin time (PT)/international normalized ratio (INR) is recommended.

Answer a is incorrect. Lisinopril does not interact with capecitabine.

Answer b is incorrect. Theoretically, HCTZ may increase risk of myelosuppression in patients receiving chemotherapy. However, this is not considered to be a clinically significant drug interaction and concomitant use of HCTZ and capecitabine is not contraindicated.

Answer d is incorrect. Cetirizine does not interact with capecitabine.

GC is a 58-year-old man with a recent diagnosis of stage IV colon cancer. His prior medical history is significant for hypertension (on lisinopril and hydrochlorothiazide [HCTZ]), deep vein thrombosis (on warfarin), and atrial fibrillation (on amiodarone). The oncologist informs the patient the plan is for him to receive neoadjuvant chemotherapy followed by surgery. The oncologist informs GC that he will receive the chemotherapy regimen XELOX (capecitabine and oxaliplatin).

  • XELOX:

  • Capecitabine 1000 mg/m2 orally twice daily for 14 days

  • Oxaliplatin 130 mg/m2 IV on day 1

  • Repeat cycle every 3 weeks

Which of the following points should the pharmacist council GC on regarding his capecitabine?

a. Take tablets with food.

b. If he has trouble swallowing the tablets, crush them and mix in applesauce.

c. Avoid eating grapefruit or drinking grapefruit juice while taking capecitabine.

d. Avoid drinking cold liquids while taking capecitabine.

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