Stability of bethanechol chloride in oral liquid dosage forms

The chemical stability of bethanechol aqueous solutions prepared using either tablets, injection or powder was studied. For an aqueous solution prepared using tablets, the initial result was low (86.5%) and the pH value was 7.1. With storage at 25 deg C, the result increased to almost 100% in 12 days and the pH value decreased to about 3.4. For the solution prepared from the injection, the initial result was 100%. After 40 days' storage at 25*C, the pH value decreased from 7.0 to 6.0 and the result was still almost 100% of the label claim. The aqueous solutions prepared from powder in phosphate buffers (pH values between 3.0 and 6.8) retained almost 100% of the potency at all pH values.