Why is glycocholic acid sodium salt better than deoxycholic acid sodium salt for the preparation of mixed micelle injections?

Classical mixed micelle systems make excellent parenteral drug carriers for lipophilic or poorly soluble drugs, but many formulations details are not fully understood and need further study. Thus, we constructed mixed micelle systems with lecithin and either glycocholic acid sodium salt or deoxycholic acid sodium salt in order to investigate the differences between the bile salts. Vitamin K1, a lipid-soluble drug, was encapsulated in the mixed micelles, and the influence of bile salts on the quality and stability of the mixed micelle systems was analyzed. Both bile salts displayed similar profiles, and the amounts of bile salts used in formulating clear solutions did not differ. Mixed micelle systems formed from glycocholic acid sodium were physically stable at low pH levels (5.5), whereas those formed from deoxycholic acid required higher pH (>8.5). High pH levels hurt active pharmaceutical ingredients that are prone to hydrolytic and oxidative degradation. Hence, when mixed micelle systems formed from deoxycholic acid sodium were sterilized, unexpected chemical unstability occurred. Therefore, we conclude that glycocholic acid sodium salt is more suitable than deoxycholic acid sodium salt for the preparation of mixed micelle injections.