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Chapter 4

PSYC62H3 Chapter Notes - Chapter 4: Polyneuropathy, Phencyclidine, Dissociation Constant


Department
Psychology
Course Code
PSYC62H3
Professor
Zachariah Campbell
Chapter
4

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Chapter 4: Properties of Drugs Wajiha Afaq 2015
Pharmacokinetic properties have a lot to do with how people use drugs. E.g. cocaine
users smoke or snort it rather than oral consummation. These methods don’t change how
the cocaine acts in brain, but determines how quick it reaches it.
Pharamacokinetic Properties and Drug Passage Through the Body
- designing drugs to pass through body is important, and many drugs fail in clinical
testing because of this.
-4 primary stages of drug’s pharmacokinetic properties:
Absorption
- Entry of a drug into the circulatory system. The drug must pass through different
membranes like mucus membrane in mouth or walls of intestine, depending on its
route of administration.
- Most therapeutic drugs are orally administered; we prefer this bc is easier than
giving ourselves an injection. After swallowing, it passes through stomach into
intestines, where drug may absorb through the stomach/intestine walls. Most drug
absorption occurs in small intestine.
- Developers must find ways to protect drug from digestive acids in the stomach,
usually done by encasing it with a tablet or capsule. The stomach acids must
dissolve enough of it to free the molecules for absorption . this balance reduces
amount of drug that actually reaches bloodstream.
- Duration of time needed for drug to pass through digestive system affects delay
for drug effects. Most drugs take several minutes to reach bloodstream, and with
intestinal absorption 15-1 hr. e.g. analgesic drug Tylenol, takes 30 minutes to
provide headache relief
-Inhalation is also done, such as asthma meds, or tobacco. This route lets drug
enter circulatory system through lungs and membranes in nose, mouth, and throat.
For some lung disorders and asthma, inhaling it brings it exactly to the area
needed for treatment. BUT, like oral, inhaling doesn’t absorb all substance to
reach bloodstream, but are more quickly absorbed than oral.
-Injection is another method, the drug is delivered into vein, providing rapid drug
effects and avoids absorption limitations. This may be used for emergencies, and
is used by drug abusers to achieve fast result and full absorption of drug.
Noncompliance to a med also results in using injections, and is used for some
psychiatric patients. To help psychiatric medical care with noncompliance, many
antipsychotics are deliverable sublingually, pill dissolves on or under tongue or
intranasal by using nasal spray
Distribution
- passage of drug through the circulatory system, it may need to cross certain
membranes to reach site of drug action. The distribution phase affects drug’s
bioavailability, the ability of a drug to reach a site of action. For psychoactive,
depends on drug reaching the CNS. To enter brain, it must past properties to pass
blood brain barrier

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Chapter 4: Properties of Drugs Wajiha Afaq 2015
- poor bioavailibity ends clinical trail testing to experimental drugs, e.g. osantant
efficiency in clinical testing was good in absorption, but higher doses failed to
provide greater improvement, suggesting that it did not permeate blood brain
barrier sufficiently to provide strong antipsychotic effects, soo basically it had
poor bioavailability.
- Placental barrier is also important to consider for drug effects, bc unlike
bloodbrain, all drugs taken by mother can permeate placental barrier and enter
placenta, which may allow harmful effects on fetus.
- Another factor to consider is nonspecific binding, which is binding of a drug to
sites that are not the intended target for drug effects. This can occur if they bind to
proteins in the bloodstream, and if they remained bound to them, they can’t cross
the barrier. Another form is depot binding, which is binding to receptors or other
parts of body that drug doesn’t affect
Metabolism
- Drug metabolism is the process of converting a drug into one or more metabolites,
most often takes place in liver, but can also happen in stomach.
- Enzymes play important role, (mostly cytochrome P450 metabolizes most drugs)
some may have poor rate of metabolism for antidepressants for e.g. and may have
few enzymes for this, thus, poor metabolizers have greater treatment sensitivity
for certain drugs bc it remains in their body for a longer time, metabolized.
- Some may be ultra rapid metabolizers, whom have greater level of enzymes,
and have weaker treatment sensitivity for certain drugs bc it remains for a shorter
time metabolized in body.
- Its important to know if someone is a fast/slow metabolizer to certain enzyme, so
that physician can give an alternative enzyme metabolizing drug blood testing is
one way to find out for personalized medicine, a method of prescribing drug’s
most appropriate for a patients unique biological makeup.
- In some cases, metabolism can occur before it reaches site of action, a process
called first pass metabolism, and may reduce the amount of drug available for
biological effects. Often occurs in orally administered drugs. E.g. BuSpar.
- Metabolites can help explain effects, as it may act in the body harmfully or with
another drug a patient is taking. It can also offer pharmacological effects of its
own, in this case, referred to an active metabolite. An active metabolite that is
converted form an inert compound is called a prodrug. Metabolites reveal
substance a person used, e.g. drug screening tests.
Elimination
- Process for how a drug leaves the body, through urine, sweat, feces, saliva, breath,
depending on drug. E.g. alcohol leves through breath.
- Drugs have elimination rate, the amount of drug eliminated from body overtime.
Physicians rely on this when prescribing how frequently drug should be
taken, and when next dose should be taken for the drug effects to reach
steady state, which is the sustained level of drug in the body. Most elimination
occurs during half-life, measuring drug concentration in blood. This type of drug
is called first-order-kinetics. But not all drugs follow this, for them, it varies by
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