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Review pertinent laboratory test results prior to dispensing warfarin

November 16, 2016

Pharmacists are reminded to review pertinent laboratory test (INR) results before dispensing prescriptions for warfarin or other vitamin K antagonist anticoagulants. The importance of this practice is highlighted in two real-life patient scenarios that occurred in Alberta last year.

Case #1: A patient went without INR monitoring for eight months despite the fact that 10 prescriptions for warfarin (indication: stroke prevention in atrial fibrillation) were dispensed for the patient during the eight month period, three of which were dispensed with a community pharmacist’s name as the prescriber. The patient presented to an Emergency Room for multiple medical problems and was found to have a critical INR >9.0. 

Case #2: A patient went without INR monitoring for six months despite the fact that one prescription for a large quantity of warfarin (indication: recurrent venous thromboembolic disease) was dispensed for the patient. The patient presented to an Emergency Room with chief complaint of increasing shortness of breath for three days. INR was found to be 1.3 and the patient was admitted with a diagnosis of extensive, bilateral acute pulmonary emboli.

Regular, ongoing monitoring of INR must be completed to ensure patient safety and desired patient outcomes. If review of Netcare coagulation results does not indicate regular or recent INR testing, please ask your patient if she/he performs portable prothrombin time/point-of-care testing at home, or if it is performed by another health professional. If YES, confirm recent INR monitoring has occurred and that results are appropriate; if NO, please order the appropriate laboratory test, or contact an appropriate regulated health professional and request that the laboratory test be ordered.

For further guidance, pharmacists can refer to the following sections of the Standards of Practice for Pharmacists and Pharmacy Technicians:

Standard 3 – pharmacists must consider appropriate information for each patient

Standard 6.1(i) – A pharmacist must determine the appropriateness of a prescription by considering relevant factors that a reasonable pharmacist would consider in the circumstances including the results of laboratory or other tests, if applicable, affect the appropriateness of the drug or blood product.

Article submitted by AHS Calgary Zone Anticoagulation Management Services