How much additional digoxin is needed for optimal therapeutic levels if the current plasma concentration is 0.4 ng/mL and the target is 1.2 ng/mL, given a Vd of 400 L?

To determine the additional amount of digoxin needed to reach the target plasma concentration, we can use the formula:

[ \text{Additional Dose} = \text{Vd} \times (\text{Target Concentration} - \text{Current Concentration}) ]

In this scenario, the volume of distribution (Vd) is 400 L, the target concentration is 1.2 ng/mL, and the current concentration is 0.4 ng/mL.

First, we calculate the difference in concentration:

[ \text{Difference} = 1.2 , \text{ng/mL} - 0.4 , \text{ng/mL} = 0.8 , \text{ng/mL} ]

Now we can substitute the values into the formula:

[ \text{Additional Dose} = 400 , \text{L} \times 0.8 , \text{ng/mL} ]

Since 1 ng/mL is equivalent to 1 mcg/L, we convert the units:

[ 400 , \text{L} \times 0.8 , \text{ng/mL} = 400 ,