Abstract
L-thyroxine sodium (L-T4) tablets have been administered to patients with hypothyroidism; however, the tablets cannot be administered to patients who are unable to take drugs orally. As the injection formulations are not supplied commercially in Japan, the L-T4 injection formulations are prepared in the hospital for use. In this study, we investigated the stability of L-T4 injection formulations and evaluated the decomposition rate constant (kd) using kinetic analysis. The L-T4 injection formulations were stored in tight and hermetic containers under -80℃, -30℃, 4℃, 20℃, and 30℃. The residual ratio of the L-T4 in the hermetic containers was higher than that in the tight container, and the kd in tight and hermetic containers at 20℃ was 44.38 × 10-3/d and 3.357 × 10-3/d, respectively. The decomposition of L-T4 in the hermetic container under 4℃ was low 1 month after the preparation. Moreover, the frozen storage significantly prevented the decomposition of L-T4, and the decomposition was low after a 6-month period. In conclusion, our results indicate that L-T4 injection formulations prepared in a hospital can maintain a satisfactory quality under refrigeration or in frozen storage for over 1 month and 6 months, respectively. These results support previous reports on L-T4 injection formulations and provide significant information for long-term stability of L-T4.
