Evaluation of the potential drug interaction of melatonin and warfarin: A case series

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Melatonin has the potential to interact with warfarin for many reasons. According to the Micromedex drug interaction database, melatonin has been associated with bleeding complications and reduced prothrombin time (PT) in four case reports of patients who received both melatonin and warfarin. However, there is no primary literature that supports this finding. The objective of this case series is to evaluate potential drug interactions between melatonin and warfarin. Ten adult patients, who admitted to Massachusetts General Hospital (MGH) (Boston, MA) between April 2011 and April 2012 and were treated with melatonin and warfarin concurrently, were evaluated. MGH is a 950-bed teaching hospital. Those 10 patients had changes in INR and PT. They are selected because they were not on any other medications that have major interactions with warfarin, did not receive other anticoagulants, chemotherapy, as needed or 1 dose of melatonin during their hospital stay. The Drug Interaction Probability Scale (DIPS) was used to evaluate the potential drug interaction, and the following outcomes were recorded for each patient: bleeding events, INR, PT, albumin, and LFTs. The 10 patients were 54 years old or older and the duration of concurrent administration of both medications ranged from 2 to 10 days. Melatonin dose was stable in all 10 patients while warfarin dose had changed (increased/ decreased) in some patients. Both INR and PT increased in most patients during concurrent administration of melatonin with warfarin and no bleeding events have been noted. By calculating DIPS score for each patient, we found that 6 patients experienced possible drug interaction, 2 had probable drug interaction, and 2 had doubtful drug interaction. LFTs and albumin were normal in most patients. In conclusion, concurrent use of melatonin and warfarin may result in INR and PT changes and affects coagulation activity. Monitoring INR and PT regularly is suggested when both medications are administered concurrently. � 2016, Zhengzhou University. All rights reserved.

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... The authors concluded that the combined use of warfarin and melatonin leads to a change in PT and INR and influences the coagulation activity. They suggested that regular monitoring of PT and INR is recommended for those concurrently receiving both drugs [82]. ...
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