The time required to establish a new steady-state plasma drug concentration when maintenance doses are changed is approximately four half-lives, the same amount of time required to establish the initial steadystate level. Because the half-life of digoxin is approximately 1.6 days, the time required to reach a new steady state is approximately 7 days. Digitoxin has a much longer half-life of approximately 7 days and the time required to reach steady state with digitoxin is approximately 4 weeks. The time required to reach steady state is independent of dose or dosage interval