Stability studies on some benzocycloheptane antihistaminic agents.

The photostability of selected benzocycloheptane antihistaminic agents, namely, loratadine (I), pizotifen (II), ketotifen fumarate (III) and cyproheptatidine (IV), was investigated. Both I and II were photolabile while III and IV were photostable. To perform stability studies on the photolabile compounds (I and II), specific stability-indicating high performance liquid chromatographic (HPLC) methods were established. The accuracy, precision and reliability of the developed HPLC methods for the assay of I and II in their pharmaceutical dosage forms were reported. Assay results for both drugs were within R.S.D. values <2%. The stability-indicating power of the developed methods was validated through study of UV-degraded solutions of I and II contained in quartz cells. The photostability of both drugs was studied under UV-irradiation at 254 nm. The photodegradation kinetics of both drugs, studied in different solvents, are also reported. TLC fractionation of photodegraded solutions of both drugs, revealed two fluorescent photodegradates of drug I. The use of UV-absorbers (ascorbic acid and p-aminobenzoic acid (PABA)) enhanced the photostability of both drugs possibly through a spectral-overlay effect.