The Use of Estimated Glomerular Filtration Rate for Dose Adjustment of Medications in the Elderly

Adverse drug effects as a consequence of inappropriate dosage are a common cause of hospitalization among the elderly. Older individuals are at a particular risk of overdosing because their kidney function decreases with advancing age and the elderly are often prescribed several pharmaceutical drugs. In addition, serum creatinine levels decrease owing to a reduction in muscle mass with age. Therefore, drug dosing based on the serum creatinine level only, instead of using assessment of the renal function, may result in overdosing of frail elderly patients. Renal function, i.e., the glomerular filtration rate can, with simple formulas, be estimated from analysis of creatinine and/or plasma cystatin C (eGFR). Such estimations performed with modern and validated formulas, as a rule present renal function normalized to the body surface area (mL/min/1.73 m2). A good estimation of how much the normal dosing interval should be prolonged, or the dose reduced, to obtain a desired plasma concentration of drugs that are mainly eliminated by glomerular filtration can be obtained by calculating the ratio between the patient’s eGFR and the normal renal function (about 90–125 mL/min/1.73 m2). Increased knowledge and use of eGFR by prescribing physicians will reduce the risk of overdosing drugs in the elderly.