Ans: A. To adjust maintenance dose of digoxin required to keep the blood levels within therapeutic range(Ref Goodman Gilman 12/e p33. 37: KDT 7/e p31, 515)Half- life of drug:Determines the maintenance dose of digoxin.Helps maintain therapeutic plasma levels.Maintenance dose also determined by creatinine clearance.Half-life of dioxin:36 to 48 hrs in patients with normal renal function.3.5 to 5 days in anuric patients.In patients with normal renal function, an oral daily maintenance dose without loading dose - steady-state blood concentration in approximately 7 days.Hence daily maintenance dose decided based on half-life ofthe drug.Usual digoxin therapeutic serum concentrations range - 0.8 to 2 ng/mL.(Note: Loading dose governed by volume of distribution).