Title: Serum Digoxin Levels Attained Following Loading Doses in Critically Ill Adults
Introduction: Digoxin may be used to improve rate control in patients with atrial arrythmias or increase cardiac inotropy. Both clinical effect and toxicity of digoxin are dictated by serum drug levels. Loading doses (LD) of digoxin are utilized to quickly attain appropriate serum levels. However, digoxin pharmacokinetics are unpredictable and altered by renal function, age, obesity, and left ventricular function – all of which may be aberrant in critical illness.
Methods: This was a retrospective study including all adult patients admitted to an intensive care unit at an academic medical center between January 1 2019 and December 31 2019 that received digoxin. Patients were excluded if they did not receive a digoxin LD or if serum levels were not obtained within 24 hours of the LD. Patient demographics were recorded including age, weight, creatinine, and left ventricular ejection fraction. The total digoxin LD was recorded. The primary outcome was the serum digoxin level obtained within 24 hours following LD. Patients who received weight-based LD of less than 0.5 mg/kg (actual body weight) were compared to patients receiving higher weight-based doses.
Results: A total of 303 patients were screened, with 39 patients being included in the final analysis. The median digoxin LD administered was 0.5 mg (range 0.25-1.25 mg) and median weight-based LD was 0.60 mg/kg (range 0.25-1.4 mg/kg). Median serum level obtained after the LD was 1.2 ng/mL (range 0.3-3.1 ng/mL). Digoxin levels returned at over 2 ng/mL following the LD in two (5%) cases. No cases of digitalis toxicity occurred. No differences in baseline demographics were present when comparing patients who received weight-based LD of < 0.5 mg/kg (n=11) compared to higher LD (n=28). Patients who received a LD of < 0.5 mg/kg achieved lower serum levels than patients who received higher LD (0.9 vs. 1.3 ng/mL, p=0.09). Patients who received a dose of < 0.5 mg/kg were less likely to have a serum drug level of ≥ 1 ng/mL following a LD (45.5% vs. 71.4%, p=0.12).
Conclusions: LD of digoxin in critically ill adults rarely produced high medication levels or toxicity. These results indicate that weight-based LD of >0.5 mg/kg may be more appropriate when targeting serum drug levels ≥ 1 ng/mL. However, sample size is small and more studies should be done to confirm these results.