U01.05.004 Clearance (CL)

Clearance (CL) is the volume of plasma that is cleared of a drug per unit time. It is a critical pharmacokinetic parameter used to assess the efficiency with which a drug is eliminated from the body. Clearance can be affected by various physiological conditions such as cardiac, hepatic, or renal dysfunction, which may impair the elimination process.

Formula for Clearance

Clearance can be calculated using the following formula:CL=Rate of elimination of the drug Drug concentration in plasma\text{CL} = \frac{\text{Rate of elimination of the drug}}{\text{Drug concentration in plasma}}CL=Drug concentration in plasma Rate of elimination of the drug

Alternatively, it can also be expressed as:CL=Vd×Ke\text{CL} = V_d \times K_eCL=Vd×Ke

Where:

VdV_dVd: Volume of distribution
KeK_eKe: Elimination constant

Factors Affecting Clearance

Cardiac Function: Decreased cardiac output can lower blood flow to elimination organs, such as the liver and kidneys, reducing clearance.
Hepatic Function: Liver disease or impairment may hinder drug metabolism, lowering clearance.
Renal Function: Kidney dysfunction reduces drug excretion, leading to decreased clearance.

Table: Clearance and Related Parameters

Parameter	Definition	Impact on Clearance
Clearance (CL)	Volume of plasma cleared of drug per unit time	Measures drug elimination efficiency
Volume of Distribution (Vd)	Theoretical volume in which the drug is distributed	Affects the amount of drug available for clearance
Elimination Constant (Ke)	Rate at which the drug is eliminated from the body	Higher Ke indicates faster drug clearance

Table: Clearance and Related Parameters

Points to Remember

Clearance (CL) is a key pharmacokinetic parameter that determines how quickly a drug is removed from the bloodstream.
Impaired cardiac, hepatic, or renal function can significantly reduce clearance, affecting drug dosing and efficacy.
Clearance is derived from the volume of distribution VdV_dVd and the elimination constant KeK_eKe, both of which influence drug elimination.
Accurate estimation of clearance is important for avoiding drug toxicity or therapeutic failure.

USMLE Step 1 Review Series

Curriculum

U01.05.004 Clearance (CL)

Formula for Clearance

Factors Affecting Clearance

Table: Clearance and Related Parameters

Points to Remember

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