Parenteral preparations incompatibilities

The use of cosolvents in small-volume parenteral preparations is often critical due to the limited volume of solution that can be administered by a single injection. Thus, the required dose of drug must often be incorporated in 1 or 2mL of solution. Table 6 lists parenteral products containing cosolvents. The cosolvents most often used include ethanol, propylene glycol, glycerin, PEG 400, and, sometimes, dimethylacetamide. Other cosolvents, such as DMSO, have been used as solvents for parenteral formulations of experimental anticancer agents however, their use is restricted due to toxicity and potential incompatibilities with plastic administration devices. ... 

Physicochemical incompatibilities are of particular concern when parenteral administration is planned. For example, certain insulin preparations should not be mixed. Similarly, the simultaneous administration of antacids or products high in metal content may compromise the absorption of many drugs in the intestine, eg, tetracyclines. The package insert and the Handbook on Injectable Drugs (see References) are good sources for this information. 

The other three classes of preservatives have been widely used in ophthalmic, nasal, and parenteral products, but not frequently in oral liquid preparations. The neutral preservatives are volatile alcohols their volatility introduces problems of odor and loss of preservative on aging in multidose preparations. The mercurials and quaternary ammonium compounds are excellent preservatives but are subject to incompatibilities.Mercurials are readily reduced to free mercury, and the quaternary compounds are inactivated by anionic substances. 

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