Synthesis and identification of the primary degradation product in a commercial ophthalmic formulation using NMR, MS, and a stability-indicating HPLC method for antazoline and naphazoline.

HPLC analysis of an anti-infective ophthalmic solution (Albalon-A), containing the active drugs naphazoline and antazoline, revealed a degradation peak of unknown identity. To elucidate the identity of the degradant, the active drugs were each hydrolyzed by refluxing at high pH, and their respective hydrolysis products were isolated and spectrally characterized by NMR, FT-IR, and MS for conclusive structure elucidation. The degradant's identity was confirmed by HPLC-MS analysis of Albalon-A ophthalmic solution to be the antazoline hydrolysis product N-[(N-benzylanilino)acetyl]ethylenediamine (IV). A stability-indicating HPLC method was then developed which was able to resolve IV from the active drugs. This HPLC method was then validated for quantitating the active drugs and IV. Validation studies demonstrated linear UV response at 280 nm, recovery > 98%, good reproducibility, and a detection limit of 2 micrograms/mL IV. Overall, the data demonstrated that the HPLC method was quantitative and specific for antazoline, naphazoline, and IV. Analysis of an expired stabilitry lot of the ophthalmic solution indicated the concentration of IV was 0.002% (w/v).