ABSTRACT
The drug product must meet the predetermined requirements of minimum potency of the active pharmaceutical ingredient and maximum concentration of known and unknown impurities. The required solubility of a drug and its solubility in water and biocompatible water-miscible solvents help decide the dosage form composition. Solubility and stability of most ionic drugs change with pH. Therefore, most pharmaceutical solutions are pH controlled using an appropriate buffer. The most important characteristics of a buffer solution are its pH, which can be calculated using the Henderson–Hasselbach equation, and its buffer capacity, which is defined as the magnitude of the resistance of a buffer to pH changes. Tinctures are alcoholic or hydroalcoholic solutions of chemical or soluble constituents of vegetable drugs. In addition to chemical stability of the drug, adequate potency of other additives critical to the stability and performance of the dosage form, such as antimicrobial agents and antioxidants, must be demonstrated throughout a product's shelf life.
