Bennett, Annals Int. If a drug is extensively excreted unchanged into urine, alteration of renal function will alter the drug elimination rate. Fortunately creatinine clearance can be used as a measure of renal function. Dose adjustment Creatinine clearance Creatinine is produced in the body by muscle metabolism from creatine phosphate.
Creatinine production is dependent on the age, weight, and sex of the patient.
Elimination of creatinine is mainly by glomerular filtration with a small percentage by active secretion. With the patient in stable condition the production is like a continuous infusion to steady state with the infusion rate controlled by muscle metabolism and the elimination controlled by renal function. Thus as renal function is reduced serum creatinine concentrations increases. Other compounds such as inulin are also used for GFR measurement. Although inulin GFR values are probably more accurate they involve administration of inulin and careful collection of urine for inulin determination.