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MON-LB099 The Association between Switching from Synthroid® and Clinical Outcomes: Retrospective Analysis of a US Database

Abstract OBJECTIVE: Compare the likelihood of negative clinical outcomes between continuous users of Synthroid® and patients who switch from Synthroid® to an alternative formulation of A/B rated levothyroxine (LT4). METHODS: Data were obtained from Optum ClinformaticsTM DataMart covering May 1, 2000 to March 30, 2016. Following a 6 month lead-in period of consistent use of Synthroid®, patients were categorized as continuous users of Synthroid® or switchers if they stopped use of Synthroid® and filled a prescription for an alternative LT4. Multivariable logistic analyses on propensity score matched cohorts examined the likelihood of an adverse clinical outcome, defined as a composite of diagnoses of chronic kidney disease (CKD), depression, fatigue, heart failure, hyperlipidemia, hypertension or obesity in the 2 years post identification as a continuous user of Synthroid® or a switcher (i.e., the post-period). The individual components of the composite endpoint and the probability of having a thyroid stimulating hormone (TSH) value out of range recommended by guidelines were also examined. All analyses controlled for patient characteristics, index dose of LT4, index copayment, general health, prior visits to an endocrinologist and prior presence of condition of interest. RESULTS: Propensity score matching resulted in a sample of 19,850 patients - 9,925 continuous uses of Synthroid® and 9,925 switchers. Multivariable analyses revealed that switchers, compared to continuous users, were 23% more likely (P<0.05) to experience the adverse composite clinical endpoint and were significantly more likely to be diagnosed with CKD, depression, fatigue, hypertension or obesity in the post-period (see Figure). Switchers were also significantly more likely to have a TSH value out-of-range post-period (odds ratio = 1.15; 95% confidence interval 1.08 - 1.23). DISCUSSION: Results suggest important potential clinical implications associated with switching from continuous use of Synthroid® to an alternative LT4 formulation. Specifically, continuous use of Synthroid® was associated with a significantly lower likelihood of being diagnosed with an adverse clinical outcome and a significantly higher likelihood of maintaining TSH in a guideline-recommended range. Results complement previous research which has shown that there was a high likelihood of achieving TSH targets as well as economic benefits associated with continuous use of Synthroid® compared to switching. CONCLUSION: Results of this large, retrospective study over an extended time horizon support clinical guideline stating that switches between alternative formulations of LT4 should generally be avoided. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.