Stability of injection solutions of vitamin B1 Part 1: Influence of chelating agents

The chelating agents EDTA, DTPA and HEDTA increase the stability of thiamine hydrochloride solutions. The stabilizing efficiency of HEDTA and DTPA is highly superior to that of EDTA. There is an optimum concentration of EDTA at which its stabilizing effect is maximum; beyond this concentration, the stability of the vitamin decreases gradually by increasing EDTA concentration. EDTA at a comparatively high concentration (10 mmole/1) catalyzes thiamine degradation. The stabilizing action of DTPA increases gradually as a function of its concentration. On the other hand, HEDTA in a very low concentration (0.5 mmole/1) affords a definite inhibitory effect on the rate of thiamine cleavage. However, increasing HEDTA concentration from 0.5 up to 3.0 mmole/1 does not increase its stabilizing efficiency. At HEDTA concentrations higher than 3 mmole/1, the stability of the vitamin increases gradually as a function of the chelating agent concentration.