Question

What is the relationship (directly proportional, inversely proportional, or no relationship) between dose, clearance, bioavailability, and steady state plasma concentration?

Answer 1

1. Clearance (CL) is directly proportional to the Dose (D) and the Bioavailability of drug (BA or F). So, Dose and Bioavailability are inversely proportional.

CL = F * D / AUC.

F is the fraction of dose available to the systemic circulation, otherwise known as Bioavailability (BA). AUC is the area under the concentration time curve.

2. Steady state plasma concentration (Css) is inversely proportional to the total plasma clearance of drug (Cl T). That is, slower the clearance (CL), more of the drug will remain in the system and higher the steady state (Css).

CSS = DR / Cl T. ( DR is the Input rate of drug ).

3. Higher doses (D) will increase the Css values. Therefore, Dose is directly proportional to steady state plasma concentration.

4. AUC = F * D/ CL , Css * constant = AUC. So,

Css * constant = F *D/ CL.

Therefore, steady state plasma concentration (Css) is directly proportional to Bioavailability (F or BA).