Pharmacokinetic Parameters (F1)

Pharmacokinetics

Study of how a drug moves through the body (ADME)

ADME

Absorption, Distribution, Metabolism, Excretion

Absorption

Movement of drug from site of administration to systemic circulation

Distribution

Reversible transfer of drug between blood and tissues

Metabolism

Chemical conversion of drug into metabolites

Excretion

Removal of unchanged drug from the body

Elimination

Irreversible loss of drug (metabolism + excretion)

What affects drug absorption

Lipophilicity, ionisation, molecular size, membrane transport

Bioavailability (F)

Fraction of administered dose reaching systemic circulation unchanged

Why is oral bioavailability reduced

First-pass metabolism and incomplete absorption

Volume of distribution (Vd)

Relationship between amount of drug in body and plasma concentration

Formula for Vd

Total drug in body divided by plasma concentration

What does high Vd mean

Drug extensively distributed into tissues

Clearance (CL)

Volume of blood cleared of drug per unit time

What does clearance represent

Efficiency of drug elimination

Formula for clearance

CL equals blood flow multiplied by extraction ratio

Extraction ratio (E)

Fraction of drug removed by an organ in one pass

What does extraction ratio of 1 mean

Complete removal of drug

What does extraction ratio of 0 mean

No drug removed

Which organs are most important for drug elimination

Liver and kidneys

What determines rate of drug elimination

Drug concentration and clearance