Question

What is steady state? How would you calculate it?

pharmacology

Answer 1

Answer :

• Steady state : steady state is the amount of drug administered is equal to the amount of drug eliminated within one dosing interval resulting in a plateau or constant serum drug level.
• Drugs with short half life reach steady state rapidly.
• Drugs with long half life take days to weeks to reach steady state.

How to calculate :

The steady state of the drug intake regards a constant mean concentration of drug in which the elimination and absorption of the drug is equal .the time to achieve steady state is relaying on the half life of drug .

Formula :

1 hlaf life : 50 % steady state achieved .

2 half lives : 75% steady state achieved .

3 half lives : 87.5% steady state achieved .

4 half lives : 93.8 steady state achieved.

Rate of input : F*dose/T ,where t is the dosing interval .

Rate of elimination : CL*Cp.

Then replacing terms from the equation For Gas above with AUC, We get the following : Css =AUC/T .

Then We will get Css = R o / CL where Ro is rate of drug input.