Detection and Characterization of an Unknown Impurity in Levothyroxine Sodium Tablets by UHPLC, LC/MS, MS/MS and MS/MS/MS

Impurities in the active ingredient of a drug are very important for the quality and reliability of the finished product. Therefore, the identification of these impurities constitutes reliability for patients using the drug. Levothyroxine sodium has known but also unknown impurities. Liothyronine sodium is known as the most common impurity of Levothyroxine sodium. Thought to be more active than levothyroxine and with a rapid (few hours) onset and short duration of action, liothyronine sodium is used in the treatment of hypothyroidism, particularly in the cases of hypothyroid coma. In our study, besides known impurities of Levothyroxine sodium, some unknown impurities were observed in samples that were exposed to heat. In these unknown impurities, the most important one that increases the fastest with the temperature that will affect the quality of the product is the impurity at RRT 0.6, according to our impurity method which was developed in-house. The impurity that increases with temperature has been defined by various identification studies, including MS/MS analysis, LC-UV detection etc. The degradation product, which was initially characterized by its retention time as RRT 0.6, was subsequently identified to be a lactose adduct of Levothyroxine API, which is formed by a Maillard reaction between Levothyroxine and lactose.