M.T., a 75-year-old, white 60kg IBW woman with a serum creatinine of 1.8 mg/dL, has atrial fibrillation. A decision has been made to use digoxin for heart failure. The target concentration of digoxin for the treatment of atrial fibrillation is 0.5 ng/mL to less than 1 ng/mL, but her current level is high at 2 ng/mL.
1. What is her estimated creatinine clearance using the Cockcroft/Gault method? GFR using the MDRD method?
2. Assuming a half-life of four days, how long will it take for M.T. to achieve a 1 ng/mL level? A 0.5 ng/mL level?