Katzung Chapter 3: Pharmacokinetics and Pharmacodynamics: Rational Dosing and the Time Course of Drug Action and Chapter 4: Drug Biotransformation

Pharmacokinetics

What the body does to the drug

Volume of distribution

Measure of apparent space in the body available to contain the drug

Clearance

Measure of the ability to eliminate a drug

First-order kinetics

Eliminationof a drug is not saturable therefore clearance is constant and the rate of elimination is proportional to the concentration of the drug

Capacity limited elimination

Clearance depends on the concentration of drug achieved and is therefore saturable

Flow-dependent elimination

The majority of the drug is eliminated in the first pass through the organ responsible for elimination

Half-life

Time required to change the amount of drug by one-half during elimination or constant infusion

Accumulation factor

One over the fraction of drug lost in one dosing interval

Bioavailability

Fraction of unchanged drug reaching the systemic circulation following administration by any route

First pass elimination

Amount of drug that is metabolized after being absorbed across the gut wall and then delivered to the liver via the portal blood system

Systemic bioavailability

Amount of drug that is absorbed after oral administration

Rate of absorption

Determined by the site of administration and the drug formulation.

Maintenance dose

Amount of drug that is given to replace the amount of drug eliminated since last dosing interval

Loading dose

Drugs with a long half-life are given as an initial higher dose to achieve the target concentration more rapidly

Maximum effect

An increase in drug concentration results in no increase in effect

Sensitivity

A lower or higher threshold to the normal pharmacological action fo a drug

Phase I reactions

Introduce or unmask polar group -OH, -NH2, -SH on drugs to make them more polar and more reactive

Phase II reactions

Glucuronic acid, sulfuric acid, acetic acid, amino acids etc. are added to drugs to make them more polar

Microsomes

Contain drug metabolizing enzymes in the endoplasmic reticulum of liver cells and other tissues

CP450 system

Enzymes in microsomes responsible for oxidizing a wide variety of lipophilic substances

Autonomic system

Motor efferent nervous system not under conscious control