The Actions of Drugs: Nomenclature, Identification, Effects, and Administration, Study notes of Community Health

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Chapter 5 Chapter 5

The Actions of Drugs

Origins of Drugs



Most drugs come from plants or are

chemically derived from plants

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

Classification of Psychoactive

Drugs

Types of 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

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 knows whether a subject is receiving an experimental drug or a placebo until the drug trial is over

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

Dose-Response Curve

Effective and Lethal Doses

 Effective dose = the dose of a drug that produces a meaningful effect in some percentage of test subjects  ED 50 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  LD 50 refers to the lethal dose for half the animal subjects in a drug test  Therapeutic index = LD 50 /ED 50  Always greater than one

Time-Dependent Factors

 Drugs vary in the timing of the onset, duration, and termination of their effects  The time course of a drug depends on how the drug is administered, how rapidly is it absorbed, and how it is eliminated from the body  Drug effects can be prolonged by taking additional doses at intervals determined by the time course of the drug  Taking multiple doses too close together will increase the maximum blood level of the drug ( cumulative effects )

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

Time-Dependent Factors

Distribution of drugs through the body

Routes of Administration:

Oral Ingestion

 Absorption from the gastrointestinal (GI) tract is a complicated process  Drugs must withstand the digestive processes and pass through the cells lining the GI tract into the bloodstream  (^) Drugs from the GI tract travel through veins first to the liver, where they may be metabolized

Routes of Administration:

Injection



Subcutaneous injection (under the skin)

 “Skin popping”  Can cause necrosis 

Intramuscular injection (into a muscle)

 Absorption is more rapid from intramuscular injection due to the greater blood supply in muscles

Routes of Administration:

Inhalation



The drug moves from

the lungs into the

bloodstream through

capillary walls



Effects are rapid

because blood moves

quickly from the lungs

to the brain