PHARMACOKINETICS
is the study of drug movement throughout the body. It involves 4 processes:
1. ABSORPTION
refers to what happens to a drug from the time it is introduced to the body until it reaches the circulating fluids and tissues.
Areas where drug can be absorbed:
GI tract (oral/rectal)
mucous membrane
skin
lungs
muscle
subcutaneous tissues
Factors Affecting Drug Absorption in the body:
a. Circulation/blood perfusion on the site of absorption
- poor circulation due to shock, vasoconstrictor drugs, or disease hampers absorption
b. Temperature
- cold causes vasoconstriction and decreases absorption; heat causes vasodilation and increases absorption
c. Drug Solubility
- the quality or condition of being soluble or the amount of a substance (water/oil) that can be dissolved in a given amount of solvent.
Lipid-soluble drugs can be easily absorbed than water-soluble drugs that usually need a carrier to be able to pass through lipid membranes.
d. Rate Limiting
Disintegration - the breakdown of a tablet into a smaller particles
Dissolution - dissolving of the smaller particles into the GI fluid before absorption; the rate of dissolution is affected by the acidity of the GI tract.
e. Route of administration
IV drugs are easily absorbed than IM, SQ and oral drugs.
ORAL MEDICATION ABSORPTION
IV MEDICATION ABSORPTION
f. First-pass Effect
-the process in which the drug passes to the liver first, which results to a large percentage of the oral dose being destroyed, never reaching the tissues.
2. DISTRIBUTION
the process by which the drug becomes available to body fluids and body tissues.
FACTORS AFFECTING DRUG DISTRIBUTION
DRUG-BINDING
NICOTINE RECEPTORS IN THE BRAIN
3. METABOLISM (BIOTRANSFORMATION)
- process by which drugs are changed into new, less active chemicals. Liver is the primary site for metabolism.
Most drugs are inactivated by liver enzymes and are then transformed by hepatic enzymes to inactivate metabolites or water-soluble substances for excretion.
4. EXCRETION
-refers to the manner at which the drug leaves the body.
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