Nonelectrolytes in Solution

Generally, nonelectrolyte or neutral drugs (such as digoxin, phenytoin, and the benzodiazepines) are dissolved in a nonaqueous or a cosolvent vehicle due to their poor solubility in water. If the drug is placed in an aqueous environment, it may form a precipitate, with concomitant loss of drug activity and/or danger to the patient. The solvents used in nonaqueous parenteral products are usually listed on the product's label. Hence, if the drug is dissolved in a water miscible solvent and one administers it slowly, dilution of the vehicle results in cosolvent fractions that maintain the drug in solution. If a cosolvent system must be used, the fraction of cosolvent in the initial stock solution should be as high as possible, to decrease the probability of precipitation upon administration.