The next few slides will review some of the mechanisms for drug interactions in more detail.  Several examples of drug interactions that occur prior to drug administration are listed here.
When phenytoin is added to solutions of dextrose, a precipitate forms and the phenytoin falls to the bottom of the IV bag as an insoluble salt.  When this happens, it is no longer available to control seizures.

Amphotericin is still used widely as a urinary bladder perfusion to treat aggressive fungal infections.  If it is administered in saline, the drug precipitates and can erode through the bladder wall if not removed. The clinical presentation of such cases is an acute abdomen due to perforation of the bladder.(Personal Communication, David Flockhart, MD, PhD., University of Indiana, July 2001)

Lastly, aminoglycosides should not be co-mixed in IV fluids with beta-lactam antibiotics  because covalent bonds are formed  between the two drugs. This can markedly reduce antibiotic efficacy.