Predicting Creatinine Clearance for Rational Dosage Adjustments in the Elderly

Abstract

It is relevant to measure the 24-hour creatinine clearance (CL_cr) for prescribing renally eliminated drugs for geriatric patients, who have diminished renal function. However, the measurement of CL_cr requires accurate sampling of 24-hour urine, which is often unreliable in the elderly. Hence, the prediction of CL_cr can serve in place of the actual measurement in dosage adjustments. Indeed, predicted CL_cr often differs from the measured CL_cr. However, it should be emphasized that the renal function of aged patients is poorly assessed by serum creatinine (S_cr) alone, while the predicted CL_cr based on S, and easily obtainable parameters, such as age and body weight, can more reasonably approximate the renal clearance of the drugs. It should be noted however, in the use of such predicted CL_cr, that the discrepancy between the predicted and measured CL_cr may not be clinically acceptable in patients with acute renal failure, liver cirrhosis, muscle wasting, and excess fluid retention.