DREXEL PSY 310 - Ch 5 The Actions of Drugs (6 pages)

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Ch 5 The Actions of Drugs



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Ch 5 The Actions of Drugs

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Pages:
6
School:
Drexel University
Course:
Psy 310 - Drugs & Human Behavior
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The Actions of Drugs Sources of Drugs Many drugs are chemically derived from plants Why do plants produce so many psychoactive drugs Names of Drugs Definitio n Chemical Complete chemical description of the molecule Example 2 diphenylmethyl sulfinyl acetamide Generic Official legal name listed in the United States Pharmacopoeia USP modafinil Categories of Drugs Stimulants produce wakefulness a sense of energy Depressants slow nervous system activity Opioids narcotics reduce pain Hallucinogens produce altered perceptions Psychotherapeutics Treat symptoms of mental disorders Some drugs belong in multiple categories Marijuana and nicotine Psychoactive Drug Classification Brand Specific drug or formulation trademarked by manufacturer Can be patented for 20 years Provigil Drug Identification Importance of identification Physicians can tell from appearance the exact drug and dose The Physician s Desk Reference PDR includes photographs of pharmaceuticals Illegal drugs are sometimes shaped marked or packaged in an identifiable way Example MDMA ecstasy Drugs can also be tested and identified through chemical analysis Types of Drug Effects Nonspecific effects Specific effects derive from the user s unique background depend on the presence of a chemical at certain expectations perceptions and environment concentrations Placebo effects are nonspecific Effects produced by an inactive chemical that the user believes to be a drug Important in treating pain and major depression Double Blind Procedure Neither the experimental participants nor the researchers know whether a subject is receiving an active drug or a placebo The blinding code is broken after drug trial is over Necessity of double blind experiments Controls for nonspecific effects in order to evaluate the effectiveness of a drug Dose Response Relationships Dose response curve graph depicting the relationship between a range of drug doses and the resulting drug effects Threshold the lowest dose at which an effect is observed Different dose response curves can be created for different drug effects Some response systems have higher thresholds Some drugs have an all or none dose response relationship Dose Response Curve Estimating the Safety Margin Safety margin the difference between Dose that produces the desired therapeutic effect in most patients Lowest dose that produces an unacceptable toxic reaction Potency Amount of a drug required to produce a given effect Side effects Unintended effects that accompany therapeutic effects Effective dose dose of a drug that produces a meaningful effect in some percentage of test subjects ED50 effective dose for half the animals in a drug test Lethal dose dose of a drug that has a lethal effect in some percentage of test subjects LD50 lethal dose for half the animals in a drug test Therapeutic index LD50 ED50 Always greater than one Most drugs have an LD1 well above the ED95 Time Dependent Factors The time course of a drug depends on how the drug is administered how rapidly is it absorbed how it is eliminated from the body Drug effects can be prolonged by taking additional doses at specific time intervals Intervals vary between drugs Taking multiple doses too close together will increase the maximum blood level of the drug o Possibly leading to cumulative effects Route of Administration Oral administratio n Insufflation snorting Intravenous injection Subcutaneou s Injection Intramuscular injection Inhalation Relatively slow absorption the most complicated way to enter the bloodstream Drugs must withstand digestive processes and pass through the cells lining the gastrointestinal tract into the bloodstream Drugs then pass through the liver where they may be metabolized Rapid onset of effects Absorption through the mucous membranes into the blood stream occurs rapidly Bypasses the liver no first pass metabolism Rapid onset of effects the drug is delivered directly into the bloodstream High concentrations can be delivered Risks Irritating material may be injected Veins may become damaged over time Blood borne diseases Under the skin Skin popping Risk can cause necrosis Into a muscle Absorption is more rapid from intramuscular injection due to the greater blood supply in muscles Rapid onset of effects The drug moves from the lungs into the bloodstream through capillary walls Thus the drug moves quickly from the lungs to the brain Transport in the Blood Drug molecules attach to protein molecules The drug is inactive in this state The drug cannot be metabolized Free unbound drug molecules can move to sites of action in the body The drug is active in this state Drugs vary in their affinity for binding with plasma proteins A drug with high affinity will displace a drug with low affinity Blood Brain Barrier In general only small lipophilic substances enter the brain Heroin is more lipophilic than morphine Thus heroin is more potent Many brain capillaries are covered with glia Also increasing the difficulty for compounds to pass out of the capillaries Active transport systems may be needed to move chemicals in and out of the brain Trauma and infections can impair the blood brain barrier Permitting more chemicals to enter the brain Mechanisms of Drug Action Effects on specific neurotransmitter systems Drugs may alter the availability of a neurotransmitter by changing the rate of o Synthesis o Metabolism o Release o Reuptake Drugs may activate or prevent the activation of a receptor Drug Interactions Combining alcohol and other depressants Respiratory depression Combining stimulants and depressants Complicated interactions Example o Methamphetamine lessens alcohol related performance disruptions o Alcohol lessens methamphetamine related sleep disruptions o Combination produces greater euphoria Drug Deactivation A drug ceases to have an effect when it is excreted unchanged from the body or is chemically changed Most important drug metabolizing liver enzymes CYP450 group of enzymes Specialized for inactivating various chemicals Many drugs have active metabolites Example marijuana and diazepam Enzyme Induction When the body s cells detect the presence of a foreign drug they trigger production of more of the specific metabolizing enzyme Important for Tolerance Interactions of drugs broken down by the same enzyme o rate of metabolism may alter effectiveness of a previously therapeutic drug dose Tolerance and Withdrawal Symptoms Drug disposition pharmacokinetic tolerance Increased metabolism or excretion reduces the


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