RESUMO
Background: The different therapeutic schedules used for the prescription of digoxin have little theoretical support. Aim: To measure digoxin plasma levels in patients using four different prescription schedules. Patients and methods: Four groups of patients were studied. Group I corresponded to 56 patients taking digoxin 0.25 mg/day, from Monday to Friday. Group II corresponded to 30 patients taking digoxin 0.25 mg/day, from Monday to Saturday. Group III corresponded to 53 patients taking digoxin 0.25 mg/day continuosly. Group IV corresponded to 36 patients taking digoxin 0.125 mg/day continuosly. Plasma digoxin levels were measured in two consecutive Mondays before taking the daily dose of the drug. Serum creatinine was also measured and creatinine clearance was calculated. The therapeutic plasma concentration range was set between 0.5 and 2 ng/ml. Results: Mean plasma digoxin levels were 1.15±0.8 ng/ml in group I, 1.4±0.55 ng/ml in group II, 1.68±0.7 ng/ml in group III and 1.14±0.43 ng/ml in group IV. 93 percent of patients in group I, 80 percent of patients in group I, 80 percent of patients in group II, 75 percent of patients in group III and 94 percent of patients in group IV had therapeutic digoxin levels. A low creatinine clearance, an age over 65 and interactions with other drugs were risk factors associated with supratherapeutic levels, mostly seen in group II and group III with 20 percent and 24 percent respectively. Conclusions: Most patients using digoxin with different therapeutic schedules had plasma drug levels within the therapeutic range