Transcript
How and Why Drugs Work
Chapter 5
Wednesday: Would you rather….
A. Find true love
B. Find $10,000,000.00
Find tr
ue love
Find $10
,000,00
0.00
0%0%Response
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.
Common Side Effects of Drugs
• Nausea or vomiting
• Changes in mental alertness
• Dependence
• Withdrawal• Allergic reactions
• Changes in cardiovascular activity
Common Side Effects of Drugs
Dose-Response
• Many factors can affect the way an individual responds to a drug, including the following:
• Dose
• Tolerance
• Potency
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
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
Margin of Safety
• The range in dose between the amount of drug necessary to cause a therapeutic effect and a toxic effect.
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
Pharmacokinetic FactorsThat Influence Drug Effects
• Administration
• Absorption
• Distribution
• Inactivation
• Biotransformation and elimination
Forms and Methods of Taking Drugs
• Oral ingestion• Inhalation• Injection• Topical application
Distribution
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.
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
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
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.
Physiological Variables That Modify Drug Effects
• Age
• Gender
• Pregnancy
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Adaptive Processes
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
• Physiological or Pharmacological tolerance: Changes causing decreased response to a set dose of a drug
• Behavioral tolerance: Drug may have the same biochemical effect but a reduced behavioral effect as a drug user learns to compensate for nervous system impairment
Drug Dependence
PhysicalDependence
(e.g.,withdrawal and rebound,
tolerance)
PsychologicalDependence
(e.g., craving, preoccupation)
Psychological Factors AffectingDrug Effect
• Individual’s mental set
• Setting or environment
• Placebo effects
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.
Addiction and Abuse (continued)
• Factors affecting variability in dependence/addiction:
• Hereditary factors (genetic variants); responsible for 40–60% vulnerability
• Drug craving
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
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