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Chapter 3

PSYC62H3 Chapter Notes - Chapter 3: Intraperitoneal Injection, Endothelium, Intrathecal Administration


Department
Psychology
Course Code
PSYC62H3
Professor
Ebs
Chapter
3

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PYSC62 Chapter 3: Basic Principles of Pharmacology
There is no commonly accepted definition of the word “drug”
o Any substance used in chemistry or medical practice
Today, many people use the word as a synonym for a narcotic agent or an illicit substance
A drug is a chemical that affects one or more biological processes however not all chemicals that
affect biological processes are considered to be drugs
o Ex. Protein, hormones, foods
According to an act, dietary supplements can now be in the market without being tested by the
FDA. The FDA may not restrict the use of any such supplements until substantial harm has been
proven
o Ex. St. John’s wort is a herbal antidepressant that has evidence for its effectiveness in
the treatment of mild to moderate cases of depression but there is also considerable
evidence for its interacting with a variety of medications in adverse ways
o These properties indicate that there is one or more ingredient in St. John’s wort that
would be considered as a drug
If the FDA could prove that tobacco companies intended for cigarettes to provide nicotine to
satisfy an addiction, the FDA would have the right to regulate them under the Federal Food,
Drug, and Cosmetic Act which considers a product to be a drug if the vendor intends it to be one
o But since tobacco companies know that nicotine is addictive thus they manipulated the
levels of nicotine to enhance the enjoyment.
o The Supreme Court ruled against allowing the FDA to regulate the tobacco products
The manufacturers of alcohol beverages prefer not to view alcohol as a drug. Thus, ethanol
should be considered a drug since it is not of any nutritional value and it affects the normal
biological activities of the body
Chemicals originating or produced in within an organism that are used to carry out the normal
biological functions in the body are not usually thought of as drugs
o Endogenous substances
Drug = nonfood, non-mechanical substance (usually a chemical substance) that exerts an effect
upon a living system
Basic Chemical Principles Related to Psychopharmacology
The largest chemical constituent of animals is water
Water molecule is polar
Water molecules are attracted to each other very powerfully = hydrogen bond
o This bonding results in the fluid characteristics of water
Water is an excellent solvent for other substances that are polar or ionic
Because many of the salts that dissolve in sea water also are present in out body fluids, life first
evolved in the sea and that terrestrial creatures could be said to carry the sea inside of us, in the
form of water and many dissolved ions
A large component of living systems is in the aqueous phase and the other phase is the organic
phase
The organic phase consists of hydrocarbons
o Fats/lipids have a high degree of hydrocarbon content
o Cholesterol is also made up of strings of hydrocarbons
The organic and aqueous phases are immiscible

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Phospholipids are a type of diglyceride
o The polar head is attracted to water while the tails are repelled by water
o These characteristics lead to the important features of the cell membranes
A lipid bilayer provides a barrier to the movement of any polar and charged substances
Any drug that is highly lipid-soluble would easily be stored in adipose tissue and if it is not
metabolized, it could stay there for a considerable time
The cell barriers between different compartments are cells and the cell membrane would
present a barrier to the diffusion of any substance that is too water-soluble and is not
transported across the membrane by proteins
The stomach and intestines are lined with cells and if a pill is introduced into the body, this
would represent the first barrier to entry into the systemic circulation
Most drugs must pass into the brain
o The BBB is made up of tight junctions between the endothelial cells that compose the
outer lining of the blood vessels
o This barrier can provide a significant resistance to the entry of drugs and other
substances into the brain, and subtle alterations in the chemical structure of drugs can
yield substantial differences in passage across the brain-blood barrier
o Ex. Scopolamine and atropine are anticholinergic drugs that readily penetrate into the
brain to produce therapeutic effects. However, there are 2 close structural analogs of
these drugs known as methlyscopolamine and methlyatropine that are much less likely
to penetrate into the brain
Ethanol is an example of a substance that is relatively soluble in water and lipid
In our body, these properties mean that ethanol easily passes from the stomach into
widespread circulation, easily dissolves in the blood, and easily passes into the brain
Marijuana (THC) which is mostly hydrocarbon and it therefore highly lipid-soluble is rapidly
absorbed when smoked and easily passes thought the BBB
Unlike ethanol, THC is not rapidly metabolized and is not very water-soluble so it deposits itself
in adipose tissue for a very long time
In order for a drug to exert any effects on an organism, it must get to its sites of action in the
nervous system
The effects of a particular drug depend heavily on the rate of accumulation and the
concentration of the drug at its sites of action and the duration of contact at those sites
o These are a function of amount of drug administered and pharmacokinetics
Pharmacokinetics = processes involved in the movement of drugs within
biological systems with respect to the drug’s absorption , distribution, binding,
or localization of tissues, metabolic alterations, and excretion from the body
Pharmacodynamics refers to the biochemical and physiological effects of drugs and their
mechanisms of action
Routes of Administration
Most common drug admission is through the mouth (per os or PO) so that the drug is absorbed
in various parts of the GI tract (this is the safest, cheapest, and most convenient way of
administering drugs)
Most drugs are thought to penetrate the GI mucosa by a process of passive diffusion, which in
turn is limited by their lipid solubility
Many drugs are weak bases or weak acids and this acidity results in their being ionized
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But since proteins in the membranes have positive and negative charges, the ionization reduces
solubility in the cellular membrane
o In order to facilitate their absorption, they are administered in the form of salt
o But since the salt dissociates in the solution, the drug may exist as both non-ionized and
ionized species
o The proportion of non-ionized to ionized drug molecules present in a given area is
important for drug absorption
The pH of the local area determines the ratio of ionized to non-ionized drug in that area
Weak acids (aspirin) are less ionized in an acid medium and are therefore more lipid-soluble
through the stomach
Alkaloids (heroin, morphine, cocaine) are poorly absorbed from the stomach
The small intestine environment favors the absorption of weak bases because of the greater
surface area and longer duration of dug contact
o This is the reason why people get intoxicated faster with carbonated alcoholic drinks;
the carbonation forces the alcohol quickly out of the stomach and into the small
intestine where it is absorbed more rapidly
IV results in rapid onset of drug action and relatively intense effects
o If over dosage occurs, little can be done unless there is a specific antagonist readily
available
o Repeated injections can lead to clot formation, vessel irritation, or vessel collapse
o There is a high incidence of allergic reaction, pronounced cardiovascular action, and side
effects with this route
Because of the good blood supply surrounding the muscles, intramuscular injection (IM)
generally results in more rapid absorption than does the PO route
o Drugs dissolved in an aqueous vehicle are more rapidly absorbed through the IM route
than when dissolved or suspended in oil
Because the lining of the inside of the lungs provides a large surface area, drug inhalation leads
to rapid onset of drug action and intense effects
o Irritants or oils can cause pneumonia and long term consequences with this route
Injection of a drug underneath the skin into the tissue between the skin and muscle is
subcutaneous drug injection (SC)
o This method can be used for non-irritating substances to produce fairly slow and even
absorption
o The rate of absorption can be controlled through the form of the drug
Sublingual or buccal administration may be used with drugs that are destroyed in the stomach
or intestines (nitroglycerin, nicotine)
Other rarely used routes include…
o Intra-arterial administration
o Bone marrow administration
o Rubbing drugs over the skin surface
o Intranasal administration
o Mucous membranes of the vagina or urethra
o Administration through the eye
o Intraperitoneal injection
Routes of administration that deliver drugs directly to the nervous system include…
o Intrathecal administration (injection into subdural space of spinal cord)
o Intracerebroventricular injection (injection into the ventricular spaces of the brain)
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