RB is a 65 yo male presenting to your outpatient clinic today after being discharged from the hospital 2 weeks ago. At the hospital, RB had a mitral mechanical valve replacement due to regurgitation, and he was started on Jantoven with unfractionated heparin used for the anticoagulation bridge. His PMH is significant for hypertension, hyperlipidemia, seizures, atrial fibrillation, and T2DM. Current medications include: Jantoven 5 mg daily, lisinopril 20 mg daily, Crestor 40 mg daily, carbamazepine 200 mg daily, and Glucophage 1000 mg BID. RB’s INR (international normalized ratio) today is 2.8 (goal of 2.5-3.5), so no change to his weekly dose of Jantoven will be made today. What key counseling points should you provide RB on his Jantoven? Select all that apply.
A. Jantoven can be affected by the amount of vitamin K you eat. Try to eat a consistent amount of foods high in vitamin K, such as spinach or kale, every week.
B. Since you have a history of atrial fibrillation, you can be switched to a direct-acting oral anticoagulant (DOAC) such as Xarelto in 3 months to limit the amounts of times you have to be monitored.
C. Carbamazepine increases Jantoven’s metabolism which may cause a decrease in your INR. It is fine to continue taking carbamazepine, however you need to consistently take it so you do not fall out of your therapeutic INR range.
D. Consuming alcohol in binge quantities will induce Jantoven’s metabolism, causing your INR to fall
E. Jantoven has a boxed warning for major bleeding which is why you need to get your INR checked regularly
Answers with rationale:
Correct answers are A, C, and E
Warfarin (Jantoven or Coumadin) is an important anticoagulant to know due to its many interactions, narrow therapeutic window, and high risk of bleeding. Unlike other anticoagulants, warfarin’s therapeutic effectiveness is measured using INR, and the range may vary depending on the indication.
Answer A is correct because warfarin works by inhibiting the subunit 1 of the multi-unit VKOR complex, thus depleting functional vitamin K reserves and hence reducing synthesis of active clotting factors. By consuming more vitamin K than normal, this will increase the available vitamin K for clotting factors to work on and decrease the INR. This puts the patient at a higher risk for a blood clot if the INR drops below the therapeutic range. Although DOACs are used in atrial fibrillation, answer B is incorrect because the patient has a mitral mechanical heart valve. These patients must remain on warfarin and cannot be switched to a DOAC due to their contraindication of use. Answer C is correct. Carbamazepine does induce warfarin’s metabolism, but if it is consistently taken it can still be used with warfarin as long as INR is frequently monitored. Answer D is incorrect because consuming high quantities of alcohol (binge drinking) will inhibit warfarin’s metabolism, not induce it. This will cause the INR to rise, not fall. There are some reports that consistent, low daily amounts of alcohol may actually induce warfarin's metabolism. Finally, answer E is correct because warfarin does have a box warning for major bleeding.
Naplex Competency Statements Covered
1.1 – Obtain, interpret, or assess data from instruments, screening tools, laboratory, genomic or genetic information, or diagnostic findings
2.1 – Pharmacology, mechanism of action, or therapeutic class
2.2 – Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names
2.3 – Boxed warnings or REMS physical descriptions; or how supplied
3.6 – Drug contraindications, allergies, or precautions
3.8 – Drug interactions
3.12 – Non-drug therapy: lifestyle, self-care, first-aid, complementary and alternative medicine, or medical equipment