Chapter 3 – Pharmacokinetics
Pharmacodynamics was concerned w/ what the drug does to the body BUT pharmacokinetics is
concerned w/ what the body does to the drug
The dynamic processes involved in the movement of drugs within biological systems w/
respect to the drug's absorption, distribution, binding or localization in tissues, metabolic
alterations and excretion from the body.
This is what determines the difference btwn 2 drugs' potency
Depends on species, age, ethnicity, genetics, psychological status, physiological status,
2 important factors in a drug's affects are it's rate of accumulation and concentration.
Depends on Solubility!
Drugs must enter the CNS to produce its' psychological effects – but drug molecules are just
too large to cross membranes
So drugs must be soluble in fat!
Drug's capability of being dissolved in fat
Most important factor in a drug's ability to pass through membranes
As drug's lipid solubility increases = better absorption from the blood = will accumulate
in tissues outside the blood = get to brain faster
So drug dissolves in blood & transported by bloodstream – but for this to happen, drugs
should also be water-soluble
Solubility in water & oil
dissolves in blood
oil/water partition coefficient
Routes of Administration
most common, safest, cheapest, & convenient
drug administered through the mouth so that it could be absorbed by the gastrointestinal
What affects absorption from G.I. Tract?
Whether drug is ionized or non-ionized
•Drugs are usually weak bases(alkaloids) or weak acids(acids)
•Weak acid: aspirin
•Alkaloids: Cocaine, heroin
•Such drugs are usually administered in the form of a salt (combo of acid & base)
•Salt exists in ionized & non-ionized form
•ionized = non fat-soluble