Approximating creatinine clearance is particularly important when prescribing medications that have a narrow therapeutic index (aminoglycosides, lithium, digoxin, procainamide, vancomycin). Even minimally excessive doses of these drugs will result in a prolonged the half-life, and an increased potential for toxic effects.
Expect and account for these alterations in drug metabolism in elderly patients. Typical changes result in increased active serum concentrations of the drug and extended half-life. Elevated drug concentrations result in more adverse drug events, and these include not only known complications, but also uncommon problems such as blood dyscrasias. If a rare adverse drug reaction does occur, it is most likely to happen in an elderly person.