Question

A patient receives an antimicrobial dose of 500mg by IV bolus every 8hrs. after steady state is reached, the concentration 2 and 7 hours after the peak are 8.9 mg/l and 4.5mg/l. what dose will attain a new css max of 20mg/l?

Answer 1

Steady state concentration in plasma (CSS max) can be calculated based on formula of the steady state calculation that is, the rate of input is equal to the rate of elimination.

Rate of input = {F*Dose}/{τ} , where τ is the dosing interval
Rate of elimination = CL*Cp
Where, solving for Cp,
we get the following = Css = Cp= {F}/{CL}*{Dose}/{τ}

Using all the above calculations and dosing values we will get 1133mg as final concentration hence,

1133mg of dose will achieve a new CSS max of 20mg/l.