Author(s): Magda M. Ibrahim*, Maha A. Hegazy and Mohamed A. Abd El- Ghani
Valsartan (VAL) and losartan potassium (LOS) are antihypertensive drugs, which are closely related in structure. Both drugs were subjected to stress conditions of hydrolysis (in acidic, neutral and alkaline media), oxidation (using hydrogen peroxide), dry heat and air. A reversed phase high performance liquid chromatographic method (RP-HPLC) was established by using acetonitrile: phosphate buffer (0.02M, pH 3.5), (60: 40 v/v) as a mobile phase at flow rate of 1.5 ml/ min and detection at 225 nm. Several factors were studied under the different experimental stress conditions. These factors include reagents concentrations, the applied temperature during stress testing and time of reaction. The degradation studies indicated that LOS is highly susceptible to oxidation, while VAL is very sensitive to acid hydrolysis and exhibits higher sensitivity to alkaline medium than LOS. The two drugs showed nearly the same stability under neutral hydrolysis. The RP-HPLC method was validated according to the ICH guidelines; the linearity range is 8-120 and 10-100 μg/mL for VAL and LOS, respectively; precision, accuracy, robustness, ruggedness, specificity were also evaluated. Thermal analysis of the two drugs was achieved in hot air oven and results show that valsartan is less thermally stable than losartan. The proposed RP-HPLC method is simple, accurate, reproducible, stability-indicating and suitable for routine determination of VAL or LOS in bulk and dosage forms.