How and Why Drugs Work

Chapter 5

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

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Common Side Effects of Drugs(continued)

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 administrated

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

Toxicitythe capacity of a drug to do damage or cause

adverse effects in the body

Potency

the amount of drug necessary to cause an 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

• Activation

• Biotransformation and elimination

Forms and Methods of Taking Drugs

• oral ingestion• inhalation• injection• topical application

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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.

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(continued)

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

Psychologicaldependence

Psychological Factors AffectingDrug Effect

• Individual’s mental set

• Placebo effects

Addiction and Abuse

• The term addiction has many meanings. It is often used interchangeably with dependence, either physiological or psychological in nature; other times, it is used synonymously with the term drug abuse.

Addiction and Abuse(continued)

• Factors affecting variability in dependence- Hereditary factors- Drug craving

Addiction and Abuse(continued)

• Other factors contributing to drug use patterns- Positive versus negative effects of drug- Peer pressure- Home, school, work environment- Mental state