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A drug that activates a receptor by binding to the receptor (a protein)-- the combination is usually reversible and when the receptor is bound to the agonist ligand, the effect of the drug is produced.



A drug that binds to the receptor without activating the receptor.
Antagonists block the action of agonists by merely getting in the way of the agonist and preventing it's binding to the receptor to produce the drug effect.
Competitive vs. Noncompetitive


Competitive antagonism

Increasing concentrations of the antagonist progressively inhibit the response to the agonist


Noncompetitive antagonism

After administration of an antagonist, even high concentrations of an agonist cannot completely overcome the antagonism.


Contributes to variability in response to drugs

changing receptor numbers


When a drug binds to a receptor, it changes the activity of the machine by...

-Enhancing its activity: propofol increases the sensitivity of the y-aminobutyric acid receptor [GABAa] to GABA
-Decreases its activity: ketamine decreases the activity of N-methyl-D-aspartate [NMDA] receptor
-Triggers a chain reaction: opioid binding to the mu opioid receptor activates an inhibitory G protein that decreases adenylyl cyclase activity



The quantitative study of the absorption, distribution, metabolism, and excretion of injected and inhaled drugs and their metabolites (what the body does to the drug).


Anesthetic solubility

Highly lipid soluble (poorly water soluble)


High fat solubility

means that the molecule will have large volume of distribution because it will be preferentially taken up by fat, diluting the concentration in the plasma


Vessel Rich Group (VRG)

Following bolus injection, the drug primarily goes to tissues that receive the bulk of arterial blood flow: the brain, heart, kidneys, and liver.


Protein binding

Only free or unbound drug can readily cross cell membranes and bind to receptors. Age, hepatic and renal disease and pregnancy can all result in decreased plasma protein concentrations.



Convers pharmacologically active, lipid-soluble drugs into water-soluble and usually inactive metabolites; exceptions are metabolism to active compounds as for diazepam and opioids (M6G is more potent than morphine; codeine is the prodrug metabolized to morphine).


Four basic pathways of metabolism

Oxidation, reduction, hydrolysis, and conjugation


Phase I reactions

Oxidation, reduction, and hydrolysis
Increase the drugs.' polarity and prepare it for phase II reactions



Cytochrome P450 enzymes are crucial for oxidation reactions. Examples of oxidation metabolism of drugs catalyzed by cytochrome p450 include hydroxylation, deamination, desulfuration, dealkylation, and dehalogenation.



Cytochrome P450 enzymes are also responsible for reduction. Under conditions of low oxygen partial pressures, cytochrome P450 enzymes transfer electrons directly to a substrate such as halothane rather than oxygen.



With glucuronic acid involves cytochrome p450 enzymes. The resulting water-soluble glucuronide conjugates and then excreted in bile and urine.



Enzymes responsible for hydrolysis of drugs, usually at an ester bond, do not involve the cytochrome p450 enzyme system. Hydrolysis often occurs outside of the liver (Remi, succ, esmolol, and ester local anesthetics are cleared in the plasma and tissues via ester hydrolysis.