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Chapter 4

PSYC62H3 Chapter Notes - Chapter 4: Endocrine Disruptor, Nmda Receptor, Nicotine


Department
Psychology
Course Code
PSYC62H3
Professor
Zachariah Campbell
Chapter
4

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CHAPTER 4: PROPERTIES OF DRUGS
DO ENVIRONMENT STIMULI CONTRIBUTE TO HEROIN TOLERANCE?
Sheppard Seigel suggested that condition changes may partly account for heroin
overdose in experienced users.
PHARMACOKINETIC PROPERTIES AND DRUG PASSAGE THROUGH THE BODY
Pharmacology consists of 2 subfields: Pharmacokinetics (how drug moves
throughout the body) and Pharmacodynamics (how drug causes biological changes
in the body)
Pharmacokinetics properties have a lot to do with how people use drugs
Different methods of intake do not change how drugs act in the brain, but determine
how quickly it reaches the brain
Pharmacokinetic issues explain the common administration methods for the drug
The process of pharmacokinetics involves factors concerning how a drug is
administered, absorbed into the bloodstream, permeates different body parts, and is
eliminated from the body
It is important for drugs to reach the site of action but designing drugs to pass
through the body is not easy
There are 4 primary stages of a drug's pharmacokinetic properties: Absorption,
Distribution, Metabolism, and Elimination (Figure 4.1)
Absorption
Process of absorption refers to the entry of drug into circulatory system
Before entering into the circulatory system, the drug must diffuse through different
membranes and into organs. The particular membrane depends largely on drug's
route of administration
Route of administration determines how much drug reaches the bloodstream and the
length of time need for absorption (Figure 4.2)
Most therapeutic drugs are taken orally in which the drug passes through the
stomach and into intestines. Most drug absorption occurs in the small intestine.
Orally administered drugs must be encased within a tablet or capsule to protect it
from digestive acids in the stomach. At the same time, much of the tablet or capsule
must be dissolved by the digestive acids to free drug molecules for absorption. This
often reduces the amount of drug that actually reaches the bloodstream
Delay for drug effects depends on the time it takes for the drug to pass through the
digestive system and also on the unique chemical properties of the drug and the
substance its delivered in.
Most drugs take several minutes to reach bloodstream. 15min to an hour for
intestinal absorption. Analgesic (pain-relieving) drug Tylenol takes 30min
Table 4.1 covers other routes of Administration
Inhalation brings the drug directly to the area needing treatment ex. albuterol for
asthma. Inhaled substances absorb more quickly than those orally administered. Ex.
tobacco takes 7 seconds to reach brain. But, not all inhaled substances reach
bloodstream

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Intravenous injection involves drug delivery into vein through hypodermic needle.
This route of admin involves no absorption limitations, absorption is full and rapid, is
preferred by users of abused drugs, and is often used in emergency by physicians or
when patient is unresponsive, ex. injection of naloxone to a patient experiencing
heroin overdose
Psychiatric medical care staff may deliver drug through intramuscular injection or
intranasally by nasal spray (if drug is sublingually deliverable) if patient refuses to
swallow antipsychotics
Distribution
Distribution refers to passage of a drug through the body which involves passing
membranes to reach site of drug action. Psychoactive drugs must pass blood-brain
barrier to reach CNS. This phase affects the drug's bioavailability, ability of drug to
reach a site of action.
Poor bioavailability ends clinical trial testing to experimental drugs (Figure 4.3)
Drugs used by mothers can permeate the placental barrier, enter placenta, and harm
the baby
Nonspecific binding - binding of the drug to sites that are not the intended target for
drug effects. This occurs by protein binding (when drug binds to proteins in the
bloodstream and as a result, it can't cross the blood-brain barrier) or by depot
binding (when drugs bind to receptors or other parts of the body that drug doesn't
affect)
Metabolism
Metabolism is the process of converting drug into one or more other products called
metabolites (product resulting of enzymatic transformation of a drug). It mostly
occurs in liver and sometimes in the stomach. Most drugs are broken down by
members of CYP-1, CYP-2, and CYP-3 cytochrome P450 enzymes
Enzymes can affect a person's response to drugs. Poor metabolizers are people
who either have fewer enzymes needed to metabolize the drug or their gene
polymorphisms have a diminished ability to metabolize the drug. These people would
have greater treatment sensitivity because the unmetabolized drug will remain in the
body longer. And ultrarapid metabolizers either they have more enzymes or greater
ability of enzymes to metabolize. They have weaker treatment sensitivity.
Blood testing for these enzymatic activities provides an important approach for
personalized medicine, a method of prescribing drugs most appropriate for a
patient's unique biological makeup
Sometimes orally administered drugs metabolize before reaching site of action
(Figure 4.4). This process is called first-pass metabolism. Ex, 90% of buspirone
(BuSpar) converts to metabolites in the stomach before reaching CNS
Metabolites may act in the body, be harmful, or interact with other drugs. Active
metabolites can offer pharmacological effects of their own. Ex. enzymes convert
quetiapine (seroquel) to metabolite N-desalkylquetiapine, which functions as an
antidepressant. Active metabolite that is converted from an inert compound is called
a prodrug (biologically active compound converted through metabolism of an inert
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