[Analysis and the stability of codeine phosphate. 2: Stability of aqueous codeine phosphate solutions]

The degradation velocity of aqueous codeine phosphate solutions is of first order. The formation of the degradation products (isomerization products) depends upon temperature, light and pH value. At pH = 3.5, codeine phosphate solutions are relatively stable. Atmospheric oxygen exerts no effect. Of the complexing agents and antioxidants tested, only citric acid and thiourea seem to be capable of reducing the rate of degradation. Besides glass ampoules, plastic containers of low-density polyethylene proved to be suited for codeine phosphate solutions.