1. How and Why Drugs Work Chapter 5

2. 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.

3. Common Side Effects of Drugs
Nausea or vomiting
Changes in mental alertness
Dependence
Withdrawal
Allergic reactions
Changes in cardiovascular activity

4. Common Side Effects of Drug

5. Dose-Response
Many factors can affect the way an individual responds to a drug, including the following:
Dose
Tolerance
Potency

6. 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

7. Dose-Response Curve

8. Margin of Safety
The range in dose between the amount of drug necessary to cause a therapeutic effect and a toxic effect.

9. 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

10. 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

11. Pharmacokinetic Factors That Influence Drug Effects
Administration
Absorption
Distribution
Inactivation
Biotransformation and elimination

12. Forms and Methods of Taking Drugs
Oral ingestion
Inhalation
Injection
Topical application

13. 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.

14. 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

15. 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

16. 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.

17. Physiological Variables That Modify Drug Effects
Age
Gender
Pregnancy
© Pixtal/SuperStock

18. 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

19. Adaptive Processes

20. 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

21. (e.g.,withdrawal and rebound)
Drug Dependence
Physical
Dependence
(e.g.,withdrawal and rebound)
Psychological
Dependence
(e.g., craving)

22. Psychological Factors Affecting Drug Effect
Individual’s mental set
Placebo effects

23. 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.

24. Addiction and Abuse (continued)
Factors affecting variability in dependence/addiction:
Hereditary factors (genetic variants); responsible for 40–60% vulnerability
Drug craving

25. 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