THE POSOLOGY AND TROUGH CONCENTRATIONS OF DIGOXIN IN ADULT AND ELDERLY PATIENTS.

Being a narrow therapeutic index drug, digoxin may cause harm if dosed without regular measurements of serum levels. Due to various limitations in its dosing, different challenges still exist in clinical practice. This study aimed to assess digoxin though concentrations after different regimens in adult and elderly patients, and to identify predictor variables for the ratio of given dose and digoxin trough level. This was prospective open-label study. Digoxin was administered per os as 0.125 or 0.25 mg during different continuous and interrupted dosage regimens. Study protocol allowed an additional therapy according to contemporary guidelines. Digoxin concentrations were determined using Abbott AxSYM Digoxin II assay in trough samples (1-3 per patient) after 3-4 weeks stable regimen. In total, 191 concentrations (104 patients) were analyzed. Digoxin weekly dose was in range 0.375-1.75 mg. On average, we observed slightly lower digoxin levels in HF patients. Results showed that in patients receiving digoxin with interrupted dosage regimen post- pause digoxin level was statistically significantly lower than pre-pause (p < 0.05). Based on multi- ple linear regression, the ratio of given dose and trough concentration was mainly predicted by clearance creatinine, and to lesser extent by patient's ideal body weight. Interrupted dosing schedule shows greater variability in drug levels comparing to continuous dosing, and it additionally causes difficulties in reaching and maintaining steady trough levels between doses. Hence, individualization of dosing regimen should be carefully guided based on target levels and not solely on clinical signs and symptoms.