Chapter 5 How and Why Drugs Work
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Transcript of Chapter 5 How and Why Drugs Work
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How and Why Drugs Work
Chapter 5
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Wednesday: Would you rather….
A. Find true loveB. Find $10,000,000.00
Find tr
ue love
Find $10
,000,00
0.00
68%
32%
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Intended and Unintended Effects of Drugs
• Intended responses:- Reason for using the drug
• Unintended responses:- Side effects
• The main distinction between intended responses and side effects depends on the therapeutic objective.
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Common Side Effects of Drugs
• Nausea or vomiting• Changes in mental alertness• Dependence
- Withdrawal• Allergic reactions• Changes in
cardiovascular activity
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Common Side Effects of Drug
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Dose-Response
• Many factors can affect the way an individual responds to a drug, including the following:- Dose- Tolerance- Potency
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Dose-Response (continued)
• Additional factors- Pharmacokinetic properties:
• Rate of absorption• Manner distributed throughout the body• Rate metabolized and eliminated
- Form of the drug- Manner in which the drug is administered
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Dose-Response
Curve
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Margin of Safety
• The range in dose between the amount of drug necessary to cause a therapeutic effect and a toxic effect.
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Potency vs. Toxicity
• Potency: The amount of drug necessary to cause an effect
• Toxicity: The capacity of a drug to do damage or cause adverse effects in the body
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Drug Interaction
• Additive effects- Summation of effects of drugs taken
concurrently• Antagonistic (inhibitory) effects
- One drug cancels or blocks effects of another
• Potentiative (synergistic) effects- Effect of a drug is enhanced by another
drug or substance
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Pharmacokinetic FactorsThat Influence Drug Effects
• Administration• Absorption• Distribution• Inactivation• Biotransformation and elimination
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Forms and Methods of Taking Drugs
• Oral ingestion• Inhalation• Injection• Topical application
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Distribution
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Distribution
• Most drugs are distributed throughout the body in the blood.
• It takes approximately 1 minute for a drug to circulate throughout the body after it enters the bloodstream.
• Drugs have different patterns of distribution depending on their chemical properties.
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Required Doses for Effects
• Threshold dose: The minimum amount of a drug necessary to have an effect
• Plateau effect: The maximum effect a drug can have regardless of the dose
• Cumulative effect: The buildup of drug concentration in the body due to multiple doses taken within short intervals
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Time-Response Factors
• The closer a drug is placed to the target area, the faster the onset of action.
• Acute drug response:- Immediate or short-term effects after a
single drug dose• Chronic drug response:
- Long-term effects after a single dose
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Biotransformation
• Biotransformation: The process of changing the chemical or pharmacological properties of a drug by metabolism.
• The liver is the major organ that metabolizes drugs in the body.
• The kidney is the next most important organ for drug elimination.
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Physiological Variables That Modify Drug Effects
• Age• Gender• Pregnancy
© Pixtal/SuperStock
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Adaptive Processes
• Tolerance: Changes causing decreased response to a set dose of a drug
• Dependence: The physiological and psychological changes or adaptations that occur in response to the frequent administration of a drug
• Withdrawal
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Adaptive Processes
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Tolerance
• Reverse tolerance (sensitization): Enhanced response to a given drug dose; opposite of tolerance
• Cross-tolerance: Development of tolerance to one drug causes tolerance to related drugs
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Drug Dependence
PhysicalDependence
(e.g.,withdrawal and rebound)
PsychologicalDependence
(e.g., craving)
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Psychological Factors AffectingDrug Effect
• Individual’s mental set• Placebo effects
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Addiction and Abuse
• The use of the term addiction is sometimes confusing. It is often used interchangeably with dependence, either physiological or psychological in nature; other times, it is used synonymously with the term drug abuse. A more accurate definition is the compulsive drug use despite negative consequences.
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Addiction and Abuse (continued)
• Factors affecting variability in dependence/addiction:- Hereditary factors (genetic variants);
responsible for 40–60% vulnerability- Drug craving
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Addiction and Abuse (continued)
• Other factors contributing to drug use patterns:- Positive versus negative effects of drug- Peer pressure- Home, school, and work environment- Mental state