2016 Volume 5 Issue 1 Pages 3-18
The gold standard for determining renal function is inulin clearance (GFR: glomerular filtration rate), but the determination of GFR is not usually performed in clinical practice because of the complexity of the procedure. Instead of the GFR, creatinine clearance is estimated by using the Cockcroft-Gault (CG) equation and estimated GFR (eGFR) for the Japanese population. Serum creatinine is affected by sex, muscle volume, and certain medications.Accurate estimation of renal function is necessary to adjust the dosage of renally excreted drugs. In this situation, eGFR (mL/min/1.73 m2) should not be used; rather, eGFR (mL/min) or CCr should be used except in the case of dosage planning where the units are indicated by mg/kg or mg/m2. In obese patients, the ideal body weight should be used in the CG equation.In regard to dosage adjustment based on CCr in package inserts, since almost all data in clinical trials had been obtained in western countries, serum creatinine determination was usually carried out using the Jaffe method. Estimation of CCr by the Jaffe method is close to the GFR. Even though CCr is mentioned in package inserts, actual measured GFR, eGFR ,or actual measured CCr×0.715 should be used as the indicators of renal function in Japan. Even though the contents of Japanese package inserts are the same as those of western countries, serious adverse effects from high-risk drugs might occur in Japan, because of the slight difference between the Jaffe method and the enzyme method of creatinine determination.When eGFR is determined to be high in thin elderly persons because of their low muscular volume, the determination of CCr by urine collection should be used, and the value should be multiplied by 0.715. GFR estimation using cystatin C is also useful. A high GFR due to augmented renal clearance is sometimes observed, particularly in young patients receiving vasoactive agents or transfusions with the systemic inflammatory response syndrome.
