Chapter 5 How and Why Drugs Work

How and Why Drugs Work

Chapter 5

Wednesday: Would you rather….

A. Find true loveB. Find $10,000,000.00

Find tr

ue love

Find $10

,000,00

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68%

32%

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 Drug

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

Dose-Response

Curve

Margin of Safety

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

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

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: 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

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

Drug Dependence

PhysicalDependence

(e.g.,withdrawal and rebound)

PsychologicalDependence

(e.g., craving)

Psychological Factors AffectingDrug Effect

• Individual’s mental set• 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