Studies on the stability of injectable solutions of some phenothiazines. Part 2: Effect of chelating agents and antioxidants.

Chelating agents (disodium EDTA, DTPA, HEDTA and NTA) exhibit a stabilizing action towards phenothiazines to different extents. This could be correlated to the stability constants of their metal chelates as well as to the dependency of these constants on the pH-value of the solution. Antioxidants (sodium bisulphite, sodium dithionite, and sodium metabisulphite) also exert a stabilizing effect which could be correlated--in the first place--to the pH-value of the solution. The sulphur content of the antioxidant might also be relevant to such an effect.