Factor affecting steady state

concentration

.

Steady state concentration• Initially amount of drug in the body is zero and hence there is no elimination.

• As the time passes amount of the drug in body rise gradually and after some point rate of elimination equal to rate of administration.

• At this point the concentration of drug in plasma approaches a constant value called as steady state concentration(Css).

Factors affecting steady state concentration

1. Infusion rate(Ro)

2. Total body clearance(CL)

Factors affecting steady state concentrationInfusion rate

• The steady state plasma drug concentration is proportional to infusion rate of drug.

• Increasing the infusion rate of drug cause the proportional increase in the steady state concentration.

• However time to reach steady state concentration is not affected by the infusion rate.

Factors affecting steady state concentrationTotal body clearance

• The steady state plasma drug concentration is inversely proportional to CLT of drug.

• Lower CLT result in higher steady state concentration.

• The same drug can have different CLT in different individuals due to difference in function of eliminating organs.

• When different values for CLT are used in the simulation while keeping the same Vd, the profile for higher CLT reaches steady state concentration faster than the profile for the lower CLT.

Reference• Mohsen A. Hedaya, Basic Pharmacokinetic, CRC publication, page no.

206-207.

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