Predictability of serum digoxin concentrations in clinical practice

A study was conducted to clarify the reliability of serum digoxin concentration (SDC) predictions in the absence of concurrent quinidine administration. The effects of age, sex, congestive heart failure (CHF), and the method used to estimate creatinine clearance were investigated. Data were collected from patients who were representative of those seen in clinical practice. Patients admitted to the study were required to have not received quinidine, to have stable renal function, to have been taking digoxin for ten consecutive days--the same dose and route of administration, and to have been categorized as having or not having CHF at the time of the SDC determination. There were 44 patients who qualified for admission to the study. SDCs were predicted on the basis of four methods for estimating creatinine clearance and four methods for estimating serum concentrations. After simple linear regression analysis, one method was found to have correlation coefficients ranging from 0.72 to 0.79, regardless of the method used to estimate creatinine clearance. In addition, analysis determined that age and presence of CHF were not factors affecting the reliability of predicted SDCs. Female patients had, on the average, a greater difference between measured and predicted SDCs; however, this was not statistically significant. Thus, in the absence of concurrent quinidine administration, SDCs may be estimated as long as the limitations of the method are acknowledged. Age, CHF, and the common methods used to estimate creatinine clearance do not significantly affect the reliability of predicted SDC values.