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Establishing Standards of Care for Amiodarone Monitoring in an Outpatient Setting

Implementing a quality-improvement project that allows for education and interdisciplinary collaboration among pharmacists, cardiologists, and primary care providers can improve rates of amiodarone monitoring.
Published Online: Jul 28,2017
Sibyl Cherian, PharmD; and Rahemat Amarshi, PharmD, MS

Objectives: To assess rates of monitoring of liver, thyroid, and pulmonary function in the 6 months before and after initiation of a quality improvement project, and to evaluate the effect of pharmacist-managed dual warfarin and amiodarone monitoring on maintaining target international normalized ratio (INR).

Study Design: Retrospective electronic chart review.

Methods: Rates of monitoring according to current guidelines for amiodarone monitoring were evaluated. Patients who filled prescriptions for a) amiodarone AND b) warfarin OR any of the following direct oral anticoagulants: apixaban, rivaroxaban, or dabigatran between May 1, 2014, and April 30, 2015, were reviewed. Percent time spent in target therapeutic INR range (% TTR) was used as an outcome parameter to evaluate effect on maintaining target INR.

Results: Seventy-three subjects were in the pre-intervention group and 69 patients were in the post intervention group. All rates of 6-month monitoring increased in the post intervention group as compared with the pre-intervention group. Both the rates of monitoring of alanine aminotransferase (P = .03) and free thyroxine (P <.001) were found to be significantly higher in the post intervention group, as compared with the pre-intervention group. The % TTR was 64% in the pre-intervention group and 58% in the post intervention group.

Conclusions: Collaboration with pharmacists in an outpatient setting leads to improved rates of recommended laboratory tests for amiodarone monitoring. This study demonstrated the effectiveness of an established anticoagulation clinic in maintaining target INR.

                                                                                             Am J Pharm Benefits. 2017;9(4);108-115

Amiodarone is a Vaughan Williams class III antiarrhythmic agent indicated for the management of ventricular fibrillation or unstable ventricular tachycardia.1 Although not currently approved by the FDA for the treatment of atrial fibrillation (AF), it has been used in the past for this condition.2,3 Amiodarone is a life-saving and effective medication, particularly in patients in whom other agents, such as calcium channel blockers and beta blockers, are contraindicated. Moreover, epidemiologists predict that there will be a rise in the prevalence of AF in North America by 2050 to more than 12 million, which is nearly a 2-fold increase from present numbers.4 Consequently, we expect to see an increase in the use of amiodarone in the future.

Due to the drug’s lipophilic properties and large volume of distribution, the drug is stored in muscle and tissue as well as in highly perfused organs, including the liver, lungs and skin. Consequently, the drug has a variable half-life, averaging about 58 days.1 It is primarily eliminated through hepatic metabolism and biliary excretion. Due to amiodarone’s complex pharmacokinetic properties and lipophilicity, it has numerous drug interactions and can cause numerous potential adverse events (AEs).1

The AEs of amiodarone range from mild—such as nausea, photosensitivity, or skin discoloration—to more serious, such as liver, thyroid, and lung toxicities.1 Amiodarone is an iodine-containing compound that is structurally similar to thyroxine. Through multiple mechanisms, amiodarone has the capability of causing hypothyroidism or hyperthyroidism.5

One of the more serious AEs is interstitial lung disease. In a study by Dusman et al, amiodarone pulmonary toxicity was found to be more common with higher doses, advanced age, lower pretreatment diffusion lung capacity for carbon monoxide (DLCO), and high plasma concentration of the active metabolite, desethylamiodarone.6 Patients who receive a total daily dose of 400 mg for 2 months or 200 mg daily for 2 years are considered at greater risk.7 Pulmonary function tests (PFTs), including DLCO, as well as chest x-rays (CXR) can help diagnose amiodarone-induced pulmonary toxicity.8