The old and new methods of assessing kidney function.

Chronic kidney disease is a worldwide problem. Accurate assessment of kidney function is important for defining stages of kidney disease and assisting with drug dosing. Glomerular filtration rate (GFR) is a good index of the health of the kidney. Although measured GFR using an exogenous substance is the most accurate, it is difficult to obtain due to cost and resources. Equations calculating creatinine clearance and estimated GFR as a measure of kidney function have been developed using serum creatinine as a marker of kidney function. The Cockcroft-Gault, Modification of Diet in Renal Disease, and Chronic Kidney Disease Epidemiology Collaboration equations have been shown to have statistically significant differences in estimating GFR in various populations. Drug-dosing adjustments based on the various equations may differ. However, without clinical outcome data, it is yet to be determined whether these differences are clinically significant.

A quantitative approach to drug dosing in chronic kidney disease.

Chronic kidney disease (CKD) is increasing at an alarming rate. Medication prescribing in this growing population is especially difficult. Many pharmacological agents or their metabolites are eliminated unchanged through the kidney. Drug dosing in CKD is challenging as most patients have a number of comorbid conditions. Patients with CKD take pharmacological agents with potential for drug interactions. Most patients also have alterations to the normal functioning of a number of different organs or systems (e.g. heart, liver, gastrointestinal system) which affect pharmacokinetics of commonly used drugs in CKD. Pharmacokinetic behaviors of most drugs are highly variable in patients with CKD. In addition, pharmacological management of patients with CKD is imprecise and requires estimating renal function, applying clinical judgment and, if available, therapeutic drug monitoring to provide adequate pharmacotherapeutic concentrations to optimize pharmacodynamic response while minimizing toxicities. For drugs that are removed through the renal system unchanged, a dosing modification should be considered according to patient- and drug-specific factors. Renal replacement therapy and dialysis remove pharmacologic agents extensively, and thus a replacement dose is needed to avoid therapeutic failure. By applying a quantitative approach, health care providers can improve pharmacotherapeutic outcomes while reducing adverse drug reactions.