Residual solvents can be classified into three classes based on their toxicity:-
Class 1 solvents are the most toxic and include compounds such as benzene, carbon tetrachloride, and chloroform. These solvents are considered to be unacceptable in pharmaceutical products because of their toxicity.
Class 2 solvents are less toxic than class 1 solvents and include compounds such as ethanol, methanol, and acetone. These solvents are considered to be acceptable in pharmaceutical products, but their levels must be controlled.
Class 3 solvents are the least toxic and include compounds such as glycerin, propylene glycol, and water. These solvents are considered to be acceptable in pharmaceutical products and their levels do not need to be strictly controlled.
