How could the drug concentration be ultimately steady in the blood without even minor changes, what is so called Css?
The steady state concentration, Css, is the concentration reached when the drug elimination rate becomes equal to drug administration rate as a result of continued drug administration. Actually it is a range of concentration and not a single concentration. For example when you give Phenytoin in a dose of 300 mg/day for more than 5 half-lives the rate of elimination will increase till it is equal to 300 mg/day. At this point you will reach a Css that fluctuates between10 and15 microgram/ml; 10 is called the trough level and 15 is called the peak level; the mean Css will be 12.5 microgram/ml. Read more…
