steady state drug conc.

[crackmle]

After starting a continuous IV infusion of a drug whose elimination half life is 2 hours,wht percentage of Css will be achieved at 6.6 hours

A. 70%

B. 87%

C. 90%

D. 94%

E. 97%

PLZ help how to calculate this.

[Dr. X]

what you're calculating for is "# of half lives".

t1/2 = 2hrs and you want to know the number of times in 6.6hrs.

that would be 6.6/2 = 3.3 times

you must memorize the chart from pg. 209 of FA which has standard values. Kind of a same thing like memorizing the confidence intervals in gaussian distribution in stats.

At 3.3, you're looking at 90%. ans - C.

I drew another box for the "# of half lives - 4, concentration at 94%". Dont forget that the number of half lives only applies when Infusion is continous at a constant rate.