High doses of Levothyroxine increase atrial fibrillation risk in elderly, finds study

Canada: The administration of levothyroxine at a dose above 0.075 mg/day in older adults may increase the risk of atrial fibrillation (AF) compared to exposure to a lower dose, suggests a recent study in the American Heart Journal.

Due to the lack of data pertaining to the effect of levothyroxine dose on the occurrence of AF are lacking, particularly in the older population, Inna Y.Gong, Department of Medicine, University of Toronto, Canada, and colleagues determine the effect of cumulative levothyroxine exposure on AF and ischemic stroke risk in older adults.

For the purpose, the researchers conducted a population-based observational study using healthcare databases from Ontario, Canada. 189,672 older adults aged ≥66 years (mean age 82 years; 72% women) without a history of AF who filled at least one levothyroxine prescription between April 1st, 2007, and March 31st, 2016 were included.

Cases were defined as cohort members who had incident AF (emergency room visit or hospitalization) between the date of first levothyroxine prescription and December 31st, 2017. Cases were matched with up to five controls without AF on the same index date. The index date was the date of AF

The secondary outcome was ischemic stroke. Cumulative levothyroxine exposure was estimated based on total milligrams (mg) of levothyroxine dispensed in the year prior to the index date. 

"Among older persons treated with levothyroxine, levothyroxine at doses above 0.075 mg/day is associated with an increased risk of AF compared to lower exposure," concluded the authors.

"Levothyroxine dose and risk of atrial fibrillation: a nested case-control study," is published in the American Heart Journal.

DOI: https://www.sciencedirect.com/science/article/abs/pii/S0002870320302726