Cockcroft and Gault equation

The Cockcroft and Gault equation cannot be used to estimate creatinine clearance in pediatric patients because muscle mass has not reached the adult proportion of body weight. Therefore/ Schwartz and colleagues (25/ 26) developed the following equation to predict creatinine clearance in these patients ... 

From the standpoint of clinical pharmacology/ the utility of using the Cockcroft and Gault equation/ or other methods/ to estimate creatinine clearance stems from the fact that these estimates can alert healthcare workers to the presence of impaired renal function in patients whose creatinine formation rate is reduced. As discussed in Chapter 5, creatinine clearance estimates also can be used to guide dose adjustment in these patients. 

Pigure 24-9 Relationship between GFR measured using l-iothalamate clearance and estimates of creatinine clearance (CrC ) obtained using the (A) Cockcroft and Gault equation and (B) measured creatinine clearance. (From Coresh JJoto RD, Kirk KA,Whelton PK, Massry S, Jones C, et at. Creatinine clearance os a measure of GFR in screenees for the African-American study of kidney disease and hypertension pilot study. Am J Kidney D/s 1998 32 32-42.)... 

They observed that the MDRD equation provided more accurate assessment of GFR than either the Cockcroft and Gault equation or measured creatinine clearance. The MDRD formula has several advantages (1) it was developed and validated in a large population, (2) it was developed with a population that included both European-Americans and African-Americans, (3) it does not require patient weight, (4) it was validated against an iothalamate clearance estimate... 

When estimating creatinine clearance in the elderly using the Cockcroft and Gault equation, some clinicians choose to round the value up to 1 if the patient s serum creatinine concentration is less than 1. Rounding the serum creatinine concentration may provide an underestimation of creatinine clearance and result in improper dose adjustment of renally eliminated medications. It is important to realize that the equation is merely an estimate, and attempts should be made to determine creatinine clearance accurately with certain medications (e.g., metformin). 

The units for Cl in Equation 1.42 are expressed in ml/min, whereas SrCr s is expressed in mg/dl, or milligrams of creatinine contained within a deciliter (100 ml) of serum. To account for the weight of females, Cl<,r determined from Equation 1.42 is multiplied by 0.85. Equation 1.42 is an approximate assessment of creatinine output and it is most accurate for patients older than 18 years of age. It is not accurate in special situations such as dosing children, the elderly people (>70 years old), or the very obese. Although other equations to calculate Cl have been developed, none has been applied clinically as extensively as Equation 1.42. In the elderly, muscle mass is proportionately less than that of individuals between 18 and 70. Between 18 and 70, corrections for age are accounted for in Equation 1.42. In spite of its limitations, the Cockcroft and Gault equation is widely used clinically. 

In Equation 1.36, Dg is the adjusted maintenance dose for the patient with renal failure, D is the maintenance dose for a normal individual,/is the fraction excreted, and C/r is the patient s creatinine clearance, which can be determined from the serum creatinine value using the Cockcroft and Gault Equation 1.42. If a new dosing interval for the patient with renal failure (x ) is calculated, a reciprocal of the bracketed term in Equation 1.45 is used and the new equation becomes Equation 1.46. ... 

In routine clinical practice it is not practical to collect the urine samples that are needed to measure creatinine clearance directly. However creatinine clearance in adult patients can be estimated either from a standard nomogram or from equations such as that proposed by Cockcroft and Gault (23). For meiy creatinine clearance can be estimated from this equation as follows ... 

The following equation by Cockcroft and Gault, which considers age, weight, sex, and serum Cr at steady state, is commonly used to estimate CrCI rate. 

In practice, there may be little to choose between the Cockcroft and Gault formula and the more recently described MDRD equation,and which is chosen will be... 

Dosage in renal impairment creatinine clearance is difficult to measure in outpatients. In patients with stable renal function, creatinine clearance (CCr) can be reasonably well estimated using the equation of Cockcroft and Gault for females CCr = (0.85) x (140-age) x (weight)/[(72) x (SCr)] for males CCr = (140-age) x (weight)/[(72) x (SCr)] where age is in years, weight is in kilograms and SCr is serum creatinine in mg/dL. 

The Cockcroft and Gault (CG) equation [6] has been shown to overestimate GFR with the use of standardized creatinine assays. The CG equation is reported in units not adjusted for body surface area (BSA), which is appropriate for drug dosage adjustment. However, it is worth noting that the CG equation considers the body weight in the mathematical approach. 

The predicted creatinine production rate in women is 85% of the calculated value, because they have a smaller muscle mass per kilogram and it is muscle mass that determines creatinine production. Muscle mass as a fraction of body weight decreases with age, which is why age appears in the Cockcroft-Gault equation. ... 

When to stop metformin in people with diabetes mellitus and abnormal renal function continues to be debated. It has been suggested that it should not be used in those with an eGFR (MDRD) of less than 60 ml/minute (122). However, this would exclude many people who have been taking metformin for many years without apparent ill effect. Others have recommended using the Cockcroft-Gault equation (SEDA-29, 527), which is preferable. 

The most commonly used equation for estimating creatinine clearance is the Cockcroft-Gault equation. This equation requires knowledge of the patient s gender, age, weight and serum creatinine. The equation is ... 

An example of this initial dosage scheme is provided in the following case. Mr. PO is a 72-year-old, 83-kg, 5-ft, 11-in man admitted to the hospital for the treatment of community-acquired pneumonia. While in the hospital, Mr. PO develops atrial fibrillation, and the decision is made to treat him with digoxin to provide ventricular rate control. His serum creatinine concentration is 2.5 mg/dL and stable. Calculate an intravenous loading dose and oral maintenance dose that will achieve a Cjj of 1.5 ng/mL. The Cockcroft-Gault equation can be... 

Calvert formula for dose modifications Dose (mg) = target AUC x (CLcr -E 25) CIcr calculated using Cockcroft-Gault equation note that the calculated dose is total dose, not dose per m body surface area Bone marrow recovery may require 6-8 weeks postadministration not a vesicant vein irritation and facial flushing may be related to alcohol vehicle... 

For adults (non-obese adults whose serum creatinine is 10mgL or higher and stable [neither increasing nor decreasing] and who do not have chronic renal failure), the Cockcroft-Gault equation is used but adjusted for men and women. For males ... 

Calculate Mr VC s renal function using both Cockcroft-Gault and the Modification of Diet in Renal Disease (MDRD) equations. 

Calculate Mr WD s renal function using the MDRD equation and the Cockcroft-Gault formula. 

A commonly used surrogate marker for actual creatinine clearance is the Cockcroft-Gault formula, which employs creatinine measurements and a patient s age and weight to predict the clearance. It is named after the scientists who first published the formula. The equation is popular because it is easy to calculate. 

---