Cystatin C may be better than creatinine for digoxin dosing in older adults with atrial fibrillation

BACKGROUND Patients taking digoxin are older with high probability of having low muscle mass, and current clinical practice in digoxin dosing relies only on estimated glomerular filtration rate from serum creatinine (eGFRcrea). The aim of the study is to compare eGFRcrea and estimated glomerular filtration rate from serum cystatin C (eGFRcys) in older adult patients with atrial fibrillation (AF) overdosed with digoxin. METHODS A total of 80 consecutive patients overdosed with digoxin and 33 controls with AF from Department of Internal Medicine were included in the prospective observational study. The median of age of participants was 81 years in both the overdosed and the control group. The eGFRs were calculated using The Chronic Kidney Disease Epidemiology (CKD- EPI) equations using standardized methods for serum creatinine and cystatin C measurement. RESULTS The median (IQR) of eGFRcrea was higher than that of eGFRcys (45 mL/min/1.73 m2 (35-59) vs 30 (21-38), respectively; P < .0001) in overdosed patients. The median (IQR) of eGFRcrea was higher than that of eGFRcys (61 mL/min/1.73 m2 (49-72) vs 40 (30-56), respectively; P < .0001) in control group of patients. Serum predose digoxin concentration in overdosed patients was inversely associated with eGFRcys (ρ = -0.26, P < .05). CONCLUSION Physicians should consider GFR when changing digoxin dosing. eGFRcys was lower in both the overdosed and the control group. eGFRcys would lead to lower digoxin doses and thus prevent overdose.