Category: Formulation and Quality
Purpose: The accurate detection and control of impurities in drug substances and products is an essential element of ICH and GMP requirements. In pharmaceutical quality control (QC) laboratories, active pharmaceutical ingredient (API) and related substances are weighed daily or weekly to make multi-analyte stock or working level solutions. This cumbersome approach introduces the potential for inconsistencies and error, especially with difficult to handle materials. Our objective was to develop Certified Pharmaceutical Impurity Solution Standards to address many of the challenges associated with compendial testing of Riboflavin and Diphenhydramine.
Methods: Riboflavin is a light sensitive compound. The system suitability solution, as specified in the European Pharmacopeia (EP) monograph, is obtained by light stress sample preparation. This solution, containing Riboflavin, Lumiflavin (EP Impurity A), and Lumichrome (EP Impurity B), is used for peak identification and resolution evaluation. The Riboflavin resolution mix was prepared by a controlled light stress protocol where the relationship of each impurity concentration and stress duration was studied. The final solution was stored in 2 ml amber ampoules flame-sealed under argon atmosphere. The stability of the final solution was investigated by performing accelerated stability assessment at conditions ranging from -80°C to 40°C over a period of 3 weeks. The effect of light exposure on samples stored at room temperature and 4°C was also investigated. A UHPLC method was developed to monitor concentration and purity across stability time-points and conditions.
A Diphenhydramine multi component solution was designed to include Diphenhydramine and each USP/EP specified impurity (EP Impurity A, Impurity B, Impurity C, Benzhydrol, Impurity E, N-oxide, USP RC-B). It was formulated in 70% acetonitrile and 30% water with 0.05% phosphoric acid at 200 µg/mL each. All single or multi-component solutions were prepared gravimetrically and sealed in ampoules under argon. The stability of these solution standards was investigated by performing accelerated stability assessment at conditions ranging from -80°C to 40°C over a period of 3 weeks. UHPLC methods were developed to monitor concentration and purity across stability time-points.
Results: Riboflavin light degradation produced Impurities A and B at levels proportional to the duration of light exposure. The optimal concentration of both impurities was achieved after 6 hours of light degradation, resulting in a ready-to-use solution that is fully compatible with the EP method (Figures 1). This Riboflavin Impurity Solution eliminates the need for the analyst to generate this reference solution. Accelerated stability assessment at conditions ranging from -80°C to 40°C over a period of 3 weeks provided evidence for long-term stability at -20°C protected from light.
The Diphenhydramine Impurity Solution containing 8 components demonstrated excellent stability across all conditions and proved to be compatible with both USP and EP methods. Single component solutions of each impurity and a Diphenhydramine System Suitability Solution (200 µg/mL API, Impurity A, and Benzhydrol) will be developed with the same formulation. The use of single component solutions allows for greater flexibility and convenience in performing drug substance and drug product testing. In routine pharma QC, analysts can simply combine the desired components into a stock solution and dilute to working level, eliminating the need to frequently weigh and prepare multi-analyte solutions (Figure 2).
Conclusion: Riboflavin and Diphenhydramine Certified Pharmaceutical Impurity Solution Standards have been developed that are traceable to primary compendial standards and certified by mass balance as ISO 17034 Certified References Materials (CRMs). These products were designed to function as stock or working level solutions in diluents proven to be compatible with USP or EP methods. Both the Riboflavin and Diphenhydramine Impurity Solutions offer an innovative and convenient alternative to preparing working level solutions for pharma QC testing.
Zongqin Ruan– Principal Scientist, MilliporeSigma, Round Rock, Texas
Shelby Waddell– Round Rock, Texas
Sarah Aijaz– Round Rock, Texas
Maysa Bakir– Round Rock, Texas
Jenna Milliken– Laramie, Wyoming
Nicolas Hauser– Laramie, Wyoming
Uma Sreenivasan– Round Rock, Texas