Excipient physical stability

In this section a study is described in which tablets prepared with binary blends of a filler-binder and a disintegrant are evaluated, with respect to their physical stability after storage under tropical conditions. With the results of this study a selection from the excipients can be made, which are suitable for use in tropical countries. Tablet formulations can be developed with the thus selected excipients. 

Some ofthe factors that affect the physical stability of emulsions include the type and concentration of surfactant used to stabilize the emulsion, the phase volume ratio (i.e., ratio of oil to aqueous phase), droplet size, compatibility of drug and excipients with the emulsion, and storage condition ofthe emulsion. 

Once good physical stability of an emulsion is insured, its commercialization mandates chemical stability of the incorporated drug and other essential components for at least 18 months. Key factors that affect the chemical stability of pharmaceutical emulsions include drug stability in oil, drug stability in aqueous media, drug concentration in oil and emulsion, phase volume ratio, droplet size, presence of excipients, and presence of air and/or peroxide radicals. As mentioned earlier, choice of appropriate antioxidant is important. 

There are some useful methods to improve the physical stability of a suspension, such as decreasing the salt concentration, addition of additives to regulate the osmolarity, as well as changes in excipient concentrations, unit operations in the process, origin and synthesis of the drug substance, polymorphic behavior of the drug substance crystals, and other particle characteristics. However, methods based on changes of the particle properties and the surfactants used are the most successful [43],... 

Knowledge of the physical stability of a formulation is very important for two reasons. First, a pharmaceutical product must look fresh and elegant as long as it remains on the shelf. Second, the active ingredient must be available to the patient throughout the expected shelf life of the product. The causes of deterioration in quality of active ingredient could be due to incompatibility with excipients, oxidation, reduction, hydrolysis, and racemization to name a few. 

The above agents are delivered in a variety of forms. Their compatibility with various solvents (propellants, alcohol, water), liquids (glycerol, polyethylene glycol, oleic acid, sorbitan trioleate, lecithin), and solid (lactose) phase excipients is key to the chemical and physical stability of the products. The Handbook of Pharmaceutical Excipients lists most of these materials.35... 

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