Considering that the Digoxin's therapeutic level is very close to its toxic level, it is important to determine the digoxin dose. Digoxin serum level is affected by multiple pharmacokinetic factors. Therefore, this study aimed to evaluate the serum digoxin level and its relation with the initial dose and other related factors in patients referred to Kashan cardiovascular clinic. Materials and Methods: This cross-sectional study was carried out on 125 patients for whom digoxin was prescribed for

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... at least one month. The patients were excluded in the case of having simultaneous history of thyroid disease and other antiarrhythmic drugs. Serum digoxin, creatinine and potassium level and also the demographic characteristics of the patients for the first time were checked out. Results: The mean age of patients was 63.7±13.42 years. Sixty-six (52.8%) cases were male. The most common reason for drug implication was systolic dysfunction (63.2%) and the most common cause of systolic dysfunction the coronary artery disease (56.61%). Most patients (70.4%) had a glomerular filtration rate (GFR) between 30-90 ml/min. Moreover, Fifty-nine patients (47.2%) with the highest frequency in treatment group were treated with 3.5 tablets per week. Serum digoxin level was significantly associated with the age and GFR (P=0.001 and P=0.008, respectively), but not with gender, potassium level and the reason for drug use and left ventricular ejection fraction. Conclusion: The main factor in determining the digoxin dose is the patient's GFR that includes all pharmacokinetic variables of drug plasma level.