PHBP Rates and Orders of Reaction

Pharmacokinetics

is the quantitative measurement of drug absorption, distribution, and elimination (ex. excretion and metabolism) and includes the rate processes for drug movement into the body, within the body, and out of the body.

rate of reaction

refers to the velocity of reaction occurs.

order of a reaction

refers to the way in which the concentration of a drug or reactant in a chemical reaction affects the rate.

Zero-order kinetics

• constant AMOUNT per unit time is metabolized

• rate does not increase as drug concentration increases

first-order kinetics

• constant FRACTION per unit time is metabolized

• rate increases as drug concentration increases

drug metabolism

zero-order kinetics

• the rate is independent of the concentration of the reactants.

• the drug concentration changes with respect to time at a constant rate.

zero order

• Followed by SUSPENSION, ALCOHOL

• Graph (conc vs time) straight line downward

• Slope = -ko

first-order kinetics

• the rate is dependent of the concentration of the reactants

• the drug concentration changes with respect to time equal the product of the rate constant and the concentration of drug remaining.

  

first-order kinetics

Followed by most of the drugs (85%)

•Graph (conc vs time) HYPERBOLA

•Graph ( log conc vs time) STRAIGHT LINE DOWNWARD

•Slope = -k/2.3

half-life

period of time required for the amount or concentration of a drug to decrease by one half

zero-order half-lfe

• not constant

• t1/2= 0.5 Co/Ko

first-order half-life

• constant

• t1/2= 0.693/k

common units used in pharmacokinetics

• zero-order rate constant

• first-order rate constant

• clearance

• half-life

zero-order rate constant

• symbol: k0

• unit: concentration/time

  • mass/time

• example: μg/mL hr & mg/hr

first-order rate constant

• symbol: k

• unit: 1/time or time^-1

• example: 1/hr or hr-1

clearance

• symbol: Cl

• unit: volume/time

• example: mL/hr

half-life

• symbol: t1/2

• unit: time

• example: hr