Health EDU

© 2008 McGraw-Hill Higher Education. All rights reserved.

Chapter 5

The Actions of Drugs

© 2008 McGraw-Hill Higher Education. All rights reserved.

Origins of Drugs

• Most drugs come from plants or are chemically derived from plants

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Names of Drugs

• Chemical name: Complete chemical description of the molecule
• Example: N'-[2-[[5-(dimethylaminomethyl)-2-furyl] methylsulfanyl]ethyl]-N-methyl-2-nitro-ethene-1,1-diamine
• Generic name: Official (legal) name, listed in the United States Pharmacopoeia (USP)
• Example: ranitidine
• Brand name: Specific drug or formulation trademarked by manufacturer; can be patented for 20 years
• Example: Zantac®

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Categories of Drugs

• Stimulants produce wakefulness, a sense of energy
• Depressants slow nervous system activity
• Opioids (narcotics) reduce pain
• Hallucinogens produce altered perceptions
• Psychotherapeutics control mental disorders
• Some drugs have effects typical of more than one category
• Marijuana
• Nicotine

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Classification of Psychoactive Drugs

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Drug Identification

• It is important that both legal and illicit drugs be identifiable by appearance
• The Physician’s Desk Reference (PDR) includes color photographs of many legally manufactured pharmaceuticals
• Illegal drugs are sometimes shaped, marked, or packaged in an identifiable way
• Drugs can be tested and identified through chemical analysis

Valium

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Nonspecific Drug Effects

• Nonspecific effects derive from the user’s unique background, expectations, perceptions, and environment (setting)
• Specific effects depend on the presence of a chemical at certain concentrations
• Placebo effects are those produced by an inactive chemical that the user believes to be a drug
• Especially important in treating pain and psychological depression

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Double-Blind Procedure

• Because of nonspecific effects, double-blind tests are needed to evaluate the effectiveness of a drug
• Neither the test subjects nor the evaluators know whether a subject is receiving an experimental drug or a placebo until the drug trial is over

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Dose-Response Relationship

• Dose-response relationship = correlation between the response and the quantity of drug administered
• Threshold = the dose at which an effect is first observed

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Dose-response graph showing size of response relative to amount of drug administered; different systems/effects have different response thresholds

Dose-Response Curve

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Effective and Lethal Doses

• Effective dose = the dose of a drug that produces an effect in some percentage of test subjects
• ED50 refers to the effective dose for half the animal subjects in a drug test
• Lethal dose = the dose of a drug that has a lethal effect in some percentage of test subjects
• LD50 refers to the lethal dose for half the animal subjects in a drug test
• Therapeutic index = LD50/ED50

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Potency, Toxicity, and Safety Margin

• Potency = strength or concentration of a drug: how much of drug to produce effect
• Toxicity = capacity of a drug to do damage or cause adverse side effects
• Safety margin = difference between
• Dose that produces the desired therapeutic effect in most patients
• Lowest dose that produces an unacceptable toxic reaction

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Time-Dependent Factors

• Duration of action- how long the effect of the drug will last
• Peak effect - time to reach the maximum effect
• Cumulative effects :Taking multiple doses too close together will increase the maximum blood level of the drug =

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Possible relationship between drug concentration in the body and measured effect of the drug

Time-Dependent Factors

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Forms and methods

of

taking drugs

oral ingestion

inhalation

injection

topical application

Routes of Administration

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Distribution of drugs through the body

© 2008 McGraw-Hill Higher Education. All rights reserved.

© 2008 McGraw-Hill Higher Education. All rights reserved.

Routes of Administration:
Oral Ingestion

• Through the mouth: but absorbed in the small intestine: takes approx. 20-30 minutes
• Drugs must withstand the digestive processes and pass through the cells lining the GI tract into the bloodstream

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Routes of Administration: Injection

• Intravenous (IV) injection: in the vein, puts the drug directly into the bloodstream

• Effects are rapid
• High concentrations can be delivered
• Veins can be damaged over time
• Infections can be directly introduced into the bloodstream

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Routes of Administration: Injection

• Subcutaneous injection (under the skin)
• Intramuscular injection (into a muscle)
• Absorption is more rapid from intramuscular injection due to the greater blood supply in muscles

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Routes of Administration: Inhalation: smoking

• The drug moves from the lungs into the bloodstream through capillary walls
• Most rapid form of administration: blood moves directly from the lungs to the brain

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Inhalation: snorting

• Absorption through the mucous membranes occurs rapidly

When a user snorts cocaine, the drug is absorbed through the mucous membranes in the nose

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Routes of Administration: Topical Application

• Absorption through the skin can provide slow, steady drug delivery (patch)
• AKA transdermal

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Transport in the Blood

• Any drug will be transported by the blood to all tissues in the body
• Action/effects will only occur at the drugs’ receptor sites
• Free (unbound) drug molecules can move to sites of action in the body
• Drugs vary in their affinity for binding with plasma proteins

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Blood-Brain Barrier

• Some drugs can’t cross the blood-brain barrier; they act only on peripheral nerves
• All psychoactive drugs pass the blood brain barrier (thus have an effect on the brain)
• If a drug passes the blood-brain barrier it will probably pass the placental barrier also
• Active transport systems may be needed to move chemicals in and out of the brain
• Trauma and infections can impair the blood-brain barrier

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Mechanisms of Drug Action

• Effects on all neurons
• Effects on specific neurotransmitter systems
• Drugs may alter the availability of a neurotransmitter by changing the rate of synthesis, metabolism, release, or reuptake
• Drugs may activate a receptor
• Drugs may prevent the activation of a receptor
• Drugs may block enzyme action

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Drug Interactions

• Additive effect – increased effect of 2 drugs taken together
• Synergist effect – effect of one drug is enhanced by the other. Very dangerous and unpredictable (potentiate)

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Drug Interactions

• Antagonist effect- one drug will cancel or reduce the effect of another

• Cocaine + alcohol produces a potent and toxic substance called cocaethylene

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Drug Deactivation

• All drugs are metabolized: you don’t stay high forever
• Half life- time it takes to metabolize half the dose (drops below threshold dose)
• The key drug-metabolizing liver enzymes are a group known as CYP450
• The resulting metabolite no longer has the same action as the drug
• The resulting metabolite can be excreted by the kidneys

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Enzyme Induction

• When the body’s cells detect the presence of a foreign drug, they trigger production of more of the specific metabolizing enzyme
• Causes tolerance
• Causes interaction of drugs broken down by the same enzyme
• Enzyme activity returns to normal some time after the inducing drug is no longer being used
• Enzyme induction and tolerance can occur after use of prescription and OTC drugs, dietary supplements, or illicit drugs

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Mechanisms of Tolerance and Withdrawal Symptoms

• (pharmacokinetic) tolerance
• Increased metabolism reduces the effect of the subsequent dose
• It takes more of the drug to reach the same effect
• Cross tolerance: high tolerance to one drug will also have high tolerance to drug in same category

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Mechanisms of Tolerance and Withdrawal Symptoms

• 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 (can’t tell if he’s stoned)
• Pharmacodynamic tolerance
• Sensitivity of neurons change after repeated use of a drug
• Can cause withdrawal reactions

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Chapter 5

The Actions of Drugs