Warfarin and Rivaroxaban Duplication A Case Repor

Authors: Julie A Fusco Eric J Paulus Alexandra R Shubat Sharminara Miah

Publish Date: 2015/06/09

Volume: 2, Issue: 1, Pages: 5-

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Abstract

A 62yearold African American man received unintentional duplicate anticoagulation therapy with warfarin 5 mg and rivaroxaban 20 mg daily for the treatment of recurrent pulmonary embolism The patient presented to the anticoagulation clinic 6 days after hospital discharge with an International Normalized Ratio INR of 23 and he was instructed to continue warfarin 5 mg daily Seven days later he returned to the clinic with an INR 80 using a pointofcare device He denied any signs or symptoms of bleeding During the interview he reported starting a new medication for neuropathy 5 days earlier The clinical pharmacist contacted the dispensing pharmacy and determined rivaroxaban 20 mg was the new medication The patient denied receiving new prescription counseling at the dispensing pharmacy Because rivaroxaban can falsely elevate INR results the actual INR value was unknown To minimize the risk for recurrent venous thromboembolism vitamin K was not administered and no warfarin doses were held Rather the patient was instructed to stop rivaroxaban and reduce the warfarin dose Five days later the patient returned with an INR of 43 He still had not experienced any signs or symptoms of bleeding The patient was quickly stabilized on a warfarin maintenance dose of 225 mg weekly The anticoagulation clinic pharmacist notified management at the clinic and at the dispensing pharmacy in an effort to identify process errors and prevent additional incidentsVenous thromboembolism VTE affects an estimated 900000 persons annually in the USA 1 Comprised of deep venous thrombosis and pulmonary embolism PE the disease represents a significant health burden For patients experiencing a thrombotic event the 30day mortality rate is 30  2 Warfarin is an effective traditional anticoagulant however a narrow therapeutic window necessitates laboratory monitoring of the International Normalized Ratio INR 3 One study found that 17  of emergency department visits for adverse drug events ADEs among older adults were related to warfarin 4 Numerous medication interactions with warfarin may be responsible for associated ADEs including bleeding 5Because of the drawbacks of warfarin medications that directly inhibit either coagulation factor II thrombin or factor Xa have more recently been developed These anticoagulants are referred to as nonvitamin K oral anticoagulants NOACs and three of these agents apixaban dabigatran etexilate and rivaroxaban are currently approved for the treatment and prevention of VTE in the USA NOACs have a faster onset shorter halflife as well as fewer medication and dietary interactions Laboratory monitoring is unnecessary because the dose response is more predictable However they are more expensive and a specific antidote does not exist 2 3 In clinical practice patients are increasingly inquiring about switching from warfarin to NOACs During the transition the potential for an ADE exists such as recurrent VTE due to inadequate anticoagulation or bleeding due to therapeutic duplication Classifying an ADE as potentially due to a medication error suggests process improvements can be madeA 62yearold African American man was referred to a pharmacistmanaged anticoagulation clinic for followup status postextensive bilateral PE The patient had received warfarin 10 mg daily for 2 days during the hospitalization then was discharged with 5 mg daily Six days after discharge the patient presented for an initial anticoagulation clinic visit with an INR of 23 goal INR 20–30 He was instructed to continue 5 mg daily and to return 7 days later At the next visit pointofcare testing revealed an INR of 80 His last dose was taken in the morning the same day The patient denied extra warfarin doses There was no suggestion of concurrent acute illness or recent alcohol intake He initially denied any new prescription or supplemental medications and stated adherence with his maintenance medications including chlorthalidone and losartan He denied signs and symptoms consistent with bruising and bleeding His active problem list included hypertension osteoarthritis sleep apnea and gout Past medical history included a PE less than 3 years earlier At that time he was maintained on warfarin 225 mg weekly for a treatment duration of 18 months Laboratory examination prior to hospital discharge revealed hemoglobin 111 g/dL hematocrit 339  and platelets 134 K/mcL Liver function tests were within the normal range The creatinine level was 175 mg/dL with an estimated creatinine clearance of 46 mL/min using ideal body weightOn further questioning the patient reported starting a new prescription medication 5 days earlier The tablet was described as small and triangular shaped The anticoagulation clinic contacted the patient’s community pharmacy and determined the medication was rivaroxaban 20 mg Communication among the anticoagulation clinic staff revealed that this prescription had been placed after the initial visit because the patient inquired about the cost of rivaroxaban with his insurance plan The community pharmacy placed the rivaroxaban prescription on hold rather than discontinue the order as the anticoagulation clinic staff had requested When the patient presented to his pharmacy the next day to pick up a different medication refill the rivaroxaban prescription had been filled and was included in the orders ready for pick up He reportedly did not receive counseling when it was dispensed He thought it was a new medication for neuropathy as this problem had been recently discussed with his primary care physician Despite reading the term ‘blood thinner’ in the medication guide the patient did not clarify its indication with the dispensing pharmacist or anticoagulation clinic He had picked up the original warfarin prescription 8 days earlier

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