Alternating Levothyroxine Preparations

Clinicians and patients often have concerns about switching between synthetic levothyroxine products. Recent data has shown that this is generally not a clinical problem. In a comparative effectiveness study evaluating changes in TSH levels after switching or not switching between generic levothyroxine products in 2780 propensity-matched patient pairs, the proportion of individuals with TSH levels within the normal range was similar in non-switchers and switchers (82.7 and 84.5 percent, respectively). If a switch from one manufacturer to another is made by the pharmacy and the patient is concerned regarding equivalent efficacy, or if maintaining the serum TSH within a narrow range is important (eg, thyroid cancer treatment), it is recommended to repeat a serum TSH level six weeks after changing preparations to ascertain that the TSH is still within the therapeutic target.