Renal elimination is an important part of drugs' excretion. At the same time, renal function can be impaired as a side effect of medication, particularly during prolonged treatments. Thus, the assessment of patients' renal function is of major consequence, especially in cases where the therapeutic regimen is adjusted taking into consideration renal clearance. Serum creatinine concentration is the most common indicator of renal clearance, since the most accurate indicator, glomerular filtration rate (GFR), is not easily measured. Using equations developed over the last decades, creatinine clearance (CLCr) is readily estimated taking into account patients' biological sex, age, body composition, and sometimes race. In this work, differences in estimated CLCr between different equations were studied and the influence of some patients' characteristics evaluated. Data collected from 82 inpatients receiving antibiotic therapy was analyzed and CLCr was estimated using a total of 12 equations. Patients were stratified according to their sex, age, and body composition to shed some light on the impact of these parameters in the estimations of renal function. More variability between estimation methods was highlighted (a) in patients between 51 and 60 years old, (b) within the normal body mass index group, and (c) in patients with serum creatinine levels below normal criteria. Furthermore, the Cockcroft-Gault equation considering lean body weight produced lower estimated CLCr in almost all groups.
Keywords: Cockcroft-Gault formula; Corcoran-Salazar formula; Jelliffe formula; Wright formula; antibiotics; creatinine clearance estimation; renal function; therapeutic drug monitoring (TDM).