Utilization of the FTIR spectroscopic method for the quantitative determination of the narrow therapeutic index levothyroxine sodium in pharmaceutical tablets

Levothyroxine sodium is a narrow therapeutic index drug used for the treatment of hypothyroidism. The medication is marketed in tablet form with very low doses ranging from 25 to 150 µg, which requires the development of a sensitive quantitative analytical method to ensure a safe and effective pharmacological response. In the present work, a Fourier transform infrared method has been developed and validated for levothyroxine sodium determination in various pharmaceutical formulations. The proposed method involves selectively extracting levothyroxine sodium from the studied tablets using chloroform as solvent, then depositing it on a KBr pellet, followed by infrared measurements and spectra analysis. The peak band area corresponding to the C=C centered at 1409 cm-1 has been chosen for the quantification. The method has been validated according to ICH guidelines and was found to be simple, precise, accurate, and specific. The linearity, detection, and quantitation limits are 25–800, 8.121, and 24.545 µg/pellet, respectively. These values confer the method’s sensitivity and applicability for the determination of different pharmaceutical tablets with various dosages. A statistical comparison with a reference HPLC method showed no significant difference. Accordingly, the developed method can be employed for quality control testing of levothyroxine sodium due to its simplicity and the absence of sophisticated instrumentation and procedures. Graphical abstract: