products present. After 8 weeks' storage, TLC was rerun, spotting 50 mcg. (as benzoyl peroxide based upon 5z labeled concentration) of each sample, together with known concentrations of benzoic acid. Estimation of the spots under long-wave UV light (366 mh) indicated approximately 10 to 13 mcg. of benzoic acid present (20 to 26Z of the labeled benzoyl peroxide concentration). Table III(B) illustrates the findings.
These results confirm the spectrophotometric findings of Gruber and Klein (1) who reported considerable loss of benzoyl peroxide dispersed in pharmaceutical preparations but not in benzoyl peroxide-calcium phosphate powder.
While benzoic acid was the only significant deteriorative product separated from benzoyl peroxide pharmaceuticals, the IR spectra and earlier polarographic studies (1) prove the presence of intermediate degradation products. While benzoyl peroxide-calcium phosphate powder exhibited no breakdown after 2 years at room temperature, once this powder was dispersed in its vehicle, decomposition followed closely with other commercial preparations, remaining stable within the period specified in its labeling.
SUMMARY
Previous spectrophotometric and polarographic analyses indicating substantial loss of benzoyl peroxide in pharmaceuticals have been corroborated. The inadequacy of conventional peroxide titration procedures is confirmed.
IR spectra of benzoyl peroxide lotions prove the formation of benzoic and/or related acids as well as aldehydes. TLC studies with semiquantitative analysis indicates degradation of benzoyl peroxide preparations stored at room temperature, with benzoic acid and/or related acids separated. Dry powdered compositions of benzoyl peroxide (benzoyl peroxide-calcium phosphate), however, indicate no breakdown after extended storage.
This study demonstrates that pharmaceutical preparations containing benzoyl peroxide possess limited shelf-life and should bear expiration dates.
While determination of certain specific degradation products in benzoyl peroxide pharmaceutical preparations has herein been determined, further investigations are being conducted in an attempt to ascertain the chemical configuration of the intermediate unstable and metastable decomposition products.