A 30 year old patient on digoxin therapy has developed digitalis toxicity. The plasma digoxin level is 4 ng/ml. Renal function is normal and the plasma t1/2 for digoxin in this patient is 1.6 days. How long should you withhold digoxin in order to reach a safer yet probably therapeutic level of 1 ng/ml?
* We want to decrease the plasma concentration of digoxin from 4 ng/ml to 1 ng/ml. * It will take two half lives (From 4 ng/ml to 2 ng/ml in one half life and from 2 ng/ml to 1 ng/ml in second half life). * Thus time required will be 2 x t 1/2 i.e. 2 x 1.6 = 3.2 days.
1.6 days
2.4 days
3.2 days
4.8 days
Pharmacokinetics