A study on the stability of terbinafine and valsartan impurity standard solutions

Abstract

A pharmaceutical molecule's stability is represented by maintaining the quality of the product's defined specification throughout its storage period, transport, dispensing and use. In this study, the stability of four pharmaceutical impurities, namely: Terbinafine EE impurity, Valsartan impurity A, Valsartan impurity B and Valsartan impurity C were studied at three different test conditions. These test conditions were: ambient temperature with light, ambient temperature in dark and refrigerated conditions. The analysis of each impurity was carried out every month, from the initial till the third time-point for Terbinafine EE and till the fourth time-point for the Valsartan impurities. At each time point, a fresh standard solution of each impurity was prepared, together with. any mobile phases and diluents needed for the HPLC analysis runs. The prepared standard solution was used both as an RSD (relative standard deviation or resolution) solution and standard solution to bracket the sample solution vials within the injection sequence. The statistical tools ANOV A two factor with replication (for Terbinafine EE, Valsartan B & C) and ANCOVA (Valsartan A) were used to determine the factors that caused a degree of instability to all four impurities. ·In addition, the student t-test tool was used to determine if the errors present between the test flasks and HPLC vials were significant or not. Furthermore, a regression analysis was carried out for each impurity at each test condition to determine the significance of their correlation. Where possible, the number of days at which the mean impurity concentration reached 90% of the initial concentration was extrapolated. This was also used to indicate the test condition at which the impurity solutions were most stable. These factors were mainly two: duration and test condition. Terbinafine EE and Valsartan impurity C solutions were affected by both factors and their interaction. On the other hand, Valsartan impurity A and B solutions were affected solely by duration. The number of storage days of Terbinafine EE impurity to reach 90% of the initial concentration were calculated to be approximately 10 days for each test condition. On the other hand, Valsartan impurity A could be stored at the refrigerator condition for around 51 days. Furthermore, both Valsartan impurities B and C solutions, could be stored for a maximum of four months at the refrigerator condition.