A natural experiment in mass media modulated pharmacokinetics after a change in tablet formulation

After a new formulation of levothyroxine was distributed in Israel, side effects were reported to the Ministry of Health 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 laboratory test performance.

Retrospective-cohort and crosssectional analysis.

All patients from the Leumit Health Services of Israel treated with levothyroxine between October 2009 and February 2012 were included in the study. A retrospective cohort was constructed of patients treated and maintained within the desired target range (0.35-5 mIU/L) from January to July 2010. A longitudinal analysis was conducted to calculate the monthly distribution of TSH levels from laboratory tests during routine care over 26 months. Data were stratified by cohort and noncohort patients.

Data were captured for 18,106 levothyroxine-treated patients; 1140 were included into the retrospective cohort. In both subpopulations a sharp rise in the number of tests performed monthly is observed at the peak of media coverage during October and November 2011. In the retrospective cohort the proportion of TSH results within target range fell to a low of 67.5% during December 2011, with 25.3% between 5.01 and 20 mIU/L. Results>20 mIU/L then peaked at 3.8% indicating an increase in patients who stopped taking levothyroxine.

These results demonstrate the power of mass media to influence patient behavior and to foment a public health scare.