Parenteral formulations infusions, stability

As a consequence, knowledge of photochemical stability and possible photochemical stability problems is of great importance in regard to parenteral preparations, especially infusions (see Table 14.1). Few systematic studies have been performed. Several factors can influence photochemical stability of dilute solutions and disperse systems, which constitute the main part of parenteral formulations. This chapter is focused on the different parameters that, theoretically, may influence photochemical stability of parenterals. Of course, the best way to stabilize the preparations is by preventing exposure to optical irradiation, an option not often accomplished in practice. Thus, it is valuable to know the factors that can influence photochemical stability of the products, as well as to prepare protocols for the management of parenterals at each hospital ward based on this knowledge. 

Clearly, physical stability is of critical importance for emulsion formulations, and care must be taken to ensure not only that the product itself is physically stable but that any infusion solutions which may be prepared by dilution of the emulsion are also physically stable over the required period of time. In addition, parenteral emulsions should be able to withstand the stresses associated with moist heat sterilization. Alternatively, if this cannot be achieved, it may be possible to prepare an emulsion aseptically from sterile components, provided the process can be suitably validated. For a good introduction to the formulation and preparation of IV emulsions, the reader is referred to Hansrani et al. (1983). 

Parenteral preparations are regularly prepared aseptically a short time or immediately prior to administration. Compounds susceptible to hydrolysis or oxidative decomposition in solution are preferentially stored as dry powders, concentrates under an inert atmosphere, or in combination with stabilizers. Concentrates for injections or infusions (European Pharmacopoeia, 2002) are diluted prior to administration, usually with sterilized Water for injection (European Pharmacopoeia, 2002) or sterile, isotonic solutions of sodium chloride, glucose, dextran, or buffer (see Table 14.3). Powders for injections or infusions (European Pharmacopoeia, 2002) are dissolved or suspended in the same media. Vitamins are aseptically added ex tempore to TPN preparations due to poor stability and the risk of precipitation (Hutchinson, 1998), as are trace metals that may influence the stability of the TPN formulation. A limited number of drugs may also be dissolved in the TPN infusion prior to administration (Hutchinson, 1998). 

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