Changes in renal function with aging. Implications for treatment.

The most important clinical renal function to monitor with aging is the glomerular filtration rate (creatinine clearance). Most decisions on drug dosage can be based on this information alone as other (tubular) functions of the kidney decrease at rates paralleling the decrease in glomerular filtration rate. As individuals age, mean creatinine clearances fall at a rate approximating 1% per year and there is an increasing variance in creatinine clearances making it increasingly important to adjust drug dosages for changes in renal function. Since muscle mass and urinary creatinine excretions decrease at nearly the same rate, mean serum creatinine concentrations stay nearly constant. One must be aware of this phenomenon when using serum creatinine concentrations alone to determine drug dosages and intervals.