Influence of Excipients and Pressing Force on the Impurity Content of N-(4-aminobenzoyl)-L-glutamic Acid in Folic Acid Drugs During Storage

Introduction. Excipients, impurities contained in them, and sorbed water are one of the reasons for degradation of the active pharmaceutical substance (API). Excipients effect should be especially evaluated for moisture-sensitive APIs. Folic acid (FA) is an important vitamin for humans. It hydrolyze in water under the action of UV irradiation and main decomposition product is N-(p-aminobenzoyl)glutamic acid (impurity A). We found an increase in the content of impurity A during FA film-coated tablets storage in PVC-film and aluminum foil packaging in the absence of UV irradiation. Aim. Investigate the effect of excipients and parameters of the production process on the content of impurity A during storage of FA drugs. Materials and methods. The FA tablets containing 1.0 mg of API produced by direct compression technology were the objects of study. The pressing force (PF) was varied from 5 to 15 kN. Results and discussion. We found that content of impurity A in tablets containing 93.0 % lactose monohydrate and obtained with PF above 10 kN exceeded limit value during storage for 300 days. Probably lactose simultaneously acts both as a source of free water and as a catalyst for FA hydrolysis. Since the interaction of lactose and FA occurs in the solid phase, pressing accelerates hydrolysis by increasing the contact area of substances and the mobility of water molecules. Conclusion. We found that lactose monohydrate probably is the main cause of FA hydrolysis in drugs. Independently of the mechanism of its action, an increase in the PF above 10 kN leads to an increase in the rate of FA hydrolysis. This is due to an increase in the mobility of water molecules and the contact area between the excipient and API. We have selected the optimum pressure range (5–10 kN) for tablet mix containing lactose monohydrate and FA.