Pace University
Affinity - ability of a drug to bind to receptor(s)
Efficacy - effect or measurable response of a drug
Agonist - drug with affinity and produces efficacy
Antagonist - drug with affinity no efficacy
Agonist = stimulant
Antagonist = blocker
DEFINITIONS OF CHEMICAL EXPOSURE
- acute exposure is defined as exposure to a chemical for less than 24 hours.
- subacute exposure - one month or less.
- subchronic exposure - 1 to 3 months.
- chronic exposure - more than 3 months.
Chemical Allergy - is an immunologically mediated adverse reaction to a chemical resulting from previous exposure to that chemical.
Chemical Idiosyncrasy refers to a genetically determined abnormal reactivity to a chemical.
Additive Effects occur when the combined effect of two chemicals is equal to the sum of the effects of each agent given alone (example 3 plus 4 = 7).
Synergistic Effects occur when the combined effects of two chemicals are greater than the sum of the effects of each agent given alone (example 2 plus 2 = 200).
Potentiation occurs when one substance does not produce an effect but when added to another chemical makes that chemical much more active (example 0 plus 2=10).
Antagonism occurs when two chemicals administered together interfere with each other's actions or one interferes with the action of the other.
There are 4 types of Antagonism:
a) functional - when two chemicals counterbalance each other by producing opposite effects;
b) chemical - when two compounds react and produce a less toxic product;
c) dispositional - when the absorption, biotransformation, distribution or excretion of a chemical is altered so that the concentration and/or duration of the chemical at the target organ is diminished;
d) receptor - when two chemicals that bind to the same receptor produce less of an effect when given together than the addition of their separate effects (example 4 plus 6=8), or when one chemical antagonizes the effect of the second chemical (example: 0 plus 4=1).
LD50 = lethal dose in 50% of test species.
ED50 = effective dose in 50% of test species.
LC50 = lethal concentration in 50% of test species (fish studies use this one).
TI= Therapeutic Index = LD/ED.
Chemicals taken ORALLY can be either WEAK ACIDS or WEAK BASES.
Weak Acids are absorbed in the acidic stomach and excreted in alkaline urine.
Weak Bases are absorbed in an alkaline (stomach/intestine) and excreted in acidic urine.
Unionized (or uncharged) chemicals cross membranes.
Ionized (or charged) chemicals bind to proteins.
Volume of distribution in L/Kg relates to the distribution of a chemical
- 0.04 or less chemical in plasma water
- 0.6 or less chemical in total body water
- greater than 0.6 chemical in lipids
- > than 1 chemical in tissue structure.