Abstract
The aim of this works is to study the thermal and photo-decomposition of levothyroxine sodium. The effect of light on the stability of the drug in solution was studied under conditions of several parameters (concentration and pH).
Photo-decomposition was carried out by exposing the drug to direct sunlight, while thermal decomposition was carried out by heating the drug at different temperatures.
Quantitative measures were carried out using high performance liquid chromatography (HPLC). Light was found to have a significant effect on the drug stability while temperature has a negligible effect at the same exposure time.
The exposure of levothyroxine sodium in solution form to direct sunlight for 80 min resulted in more than 60% decomposition. On the other hand, temperature of up to 100 degrees C has no effect. The drug seems to be stable in acidic medium. Attempts to isolate the photo-decomposition degradation products of the drug were made.
The photo-decomposition of the drug was found to follow zero-order kinetics with correlation coefficient of 0.98.
Levothyroxine sodium undergoes photo-decomposition reaction and is not stable in the presence of sunlight.
Unless the manufacturing process is carefully consistently controlled, orally administrated levothyroxine sodium products may not be fully potent through the label expiration date.