Chapter 1 Pharmacology: the science of drug action
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Cours
PSYC 450 (PSYC450)
Établissement
Athabasca University (AU
)
Chapter 1 of the document delves into the fundamental aspects of pharmacology, the science of drug action. It highlights the historical use of plants in medicine, referencing ancient Egyptian and Indian texts that detail remedies for various ailments. The chapter also emphasizes the ongoing relianc...
Pharmacology: the science of drug action
• Pharmacology studies the actions of drugs and their e ects on living organisms.
• Plants have been a signi cant part of ancient human life, with writings from 1500 BCE
describing plant-based medicines in Egypt and India.
• The Ebers Papyrus describes over 700 remedies for various ailments, including crocodile
bites, baldness, constipation, headache, and heart disease.
• Modern drugs like castor oil and opium are also mentioned.
• The Chinese have a long tradition of using herbal remedies, with estimates suggesting 80%
of people in developing countries are completely dependent on herbs or plant-derived
medicinals.
• In the United States, modern herbal medicines and natural products represented half of the
top 20 drugs on the market in 1999.
• Despite limited clinical support, many Americans are enamored with herbal remedies due to
their perceived "natural" nature.
• Neuropharmacology and psychopharmacology are two specialized areas of pharmacology,
focusing on drug-induced changes in the nervous system and mood, thinking, and behavior.
• Drug action refers to speci c molecular changes produced by a drug when it binds to a
speci c target site or receptor, leading to alterations in physiological or psychological
functions.
Understanding Drug E ects and Their Characteristics
Drug E ects:
• Drugs act at various target sites, resulting in multiple e ects.
• Some are therapeutic e ects, causing desired physical or behavioral changes.
• Other e ects are side e ects, ranging from mildly annoying to distressing and dangerous.
• Examples include amphetamine-like drugs producing alertness, insomnia, increased heart
rate, and decreased appetite.
• Drugs can also be used as a diet control in weight-reduction programs, causing insomnia and
hyperactivity.
Drug Characteristics:
• There are no "good" or "bad" drugs; all drugs are chemicals.
• The way a drug is procured and used determines its character.
• Some drugs, like alcohol, are considered "good" under certain conditions but can lead to
addiction when misused.
• Many "good" prescription drugs are illicitly acquired or misused, leading to "bad" outcomes.
Speci c and Nonspeci c Drug E ects:
• Speci c drug e ects are based on physical and biochemical interactions with a target site in
living tissue.
• Nonspeci c drug e ects are in uenced by an individual's background, mood, expectations,
perceptions, and attitude towards the drug-administering person.
Placebo e ect
• Plaque is not a "fake" pill but a pharmacologically inert compound with therapeutic and side
e ects.
• Belief in a drug can produce physiological e ects, including measurable changes like altered
gastric acid secretion, blood vessel dilation, and hormonal changes.
• A study showed that 70% of patients found signi cant relief from a placebo, while only 25%
were helped by the "drug."
, • The e ectiveness of a sugar pill depends on the ritual of the therapeutic treatment, which can
have both neurobiological and behavioral e ects.
• There is increasing interest in understanding the mechanism responsible for the placebo
e ect to enhance the therapeutic e ectiveness of drug treatments.
• Placebo e ects may be explained by Pavlovian conditioning, where symptom improvement is
associated with speci c characteristics of a medication, a recommending clinician, or aspects
of the medical facility.
• Deception is not necessary as patients bene t even if they are told the medication is a
placebo.
Placebo E ect and Its Contributions
• The placebo e ect may be in uenced by conscious, explicit expectation of outcomes.
• Individuals who anticipate relief may show an enhanced placebo response.
• Placebo-induced neurobiological e ects within the brain are signi cant.
• Subjects who anticipate pain relief show reduced neural activity in pain-related brain regions.
• Other factors may contribute to the placebo e ect, including social learning, anticipating a
positive outcome, and genetic variants.
• Negative expectations can increase anxiety and in uence treatment outcomes.
• The nocebo e ect, where expecting treatment failure and verbal suggestions of negative
outcomes increase anxiety and neural mechanisms, can be reduced by antianxiety drug
treatment.
• Nocebos are important to study as warnings about potential side e ects can lead to greater
side-e ect occurrence.
• The placebo is essential in pharmacology to eliminate the in uence of expectation on the
experiment’s participants.
• Some researchers use an “active” placebo or leave the placebo group untreated if an
e ective agent is available.
Double-Blind Experiments in Clinical Research
• Nonspeci c factors and variable placebo responders contribute to double-blind experiments.
• No participant or observer knows treatment received.
• Precautions prevent bias in treatment results.
• Brown (1998) and Louhiala (2009) provide more on placebo use in clinical research and
therapeutics.
Pharmacokinetic factors determine drug action
Drug Action Factors
• Chemical structure of a drug determines action.
• Dosage and bioavailability are key contributors.
• Dynamic factors contribute to bioavailability.
• These factors form the pharmacokinetic component of drug action.
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, Methods of drug administration in uence the onset of drug action
- The route of administration of a drug determines how much and how quickly its e ect occurs
- Systemic routes of administration distribute drugs throughout the entire body, while enteral
methods use the gastrointestinal tract
- Oral administration is the most commonly used route for drugs as it is safe, self-administered,
and economical
- Drugs must dissolve in stomach uids and pass through the stomach or intestine wall to
reach blood capillaries to be e ective
- Absorption is the movement of the drug from the site of administration to the blood
circulation
- Factors such as food in the stomach, physical activity, and rst-pass metabolism can
in uence the rate of absorption
- Some therapeutic drugs taken orally may undergo extensive metabolism, reducing their
bioavailability
- Drug plasma levels are more irregular and unpredictable and rise more slowly than those
produced by other methods of
administration due to these factors.
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