A Retrospective Analysis of TSH Levels in Levothyroxine-Treated Patients Before and After a Change in Tablet Formulation: A Natural Experiment in Mass-Media Modulated Pharmacokinetics

Background: After a new formulation of levothyroxine was distributed in Israel, side effects began to be reported generating extensive media coverage.  The purpose of this study was to determine whether the new formulation was associated with a change in thyroid-stimulating-hormone (TSH) levels of treated patients and to evaluate the effect of the extensive media-coverage on the incidence of lab test performance.
Methods: All patients from the Leumit Health Fund treated with levothyroxine between October 2009 and February 2012 were included in the study.  A retrospective cohort was constructed of a subpopulation of patients maintained within desired target range from January to July 2010.  Data was stratified for cohort and non-cohort patients.  
Results: Data were captured for 18,106 patients. 1,140 were included into the retrospective cohort.  In both sub-populations a sharp rise in the number of tests performed monthly is observed at the peak of the media coverage. In the retrospective cohort the proportion of TSH results within target-range fell to a low of 68.6% during December 2011, peaking at 3.5% indicating an increase in patients who had stopped taking levothyroxine.
Conclusions: These results demonstrate the power of the mass-media to both influence patient-behavior and to foment a public health scare.