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Pharmacology: The Science of Drug Action

Chapters 4 and 5. Pharmacology: The Science of Drug Action. Pharmacology. Pharmacokinetics Explains the processes involved in administration, absorption, distribution, transformation, and elimination a drug Pharmacodynamics

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Pharmacology: The Science of Drug Action

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  1. Chapters 4 and 5 Pharmacology: The Science of Drug Action

  2. Pharmacology • Pharmacokinetics • Explains the processes involved in administration, absorption, distribution, transformation, and elimination a drug • Pharmacodynamics • Explains the nature of physiological and biochemical interactions between a drug and the target tissue responsible for the drug effect

  3. Pharmacokinetics • Administration • Absorption • Distribution • Biotransformation • Excretion

  4. Routes of Administration • Oral • Intramuscular (IM) • Intraperitoneal (IP) • Intravenous (IV) • Inhalation • Intracranial (IC) • Intracerebroventricular • Topical

  5. Absorption • Moving from the site of administration to the bloodstream • Drugs exert effects by first traveling into the bloodstream • How fast do drugs leave the site of administration? • Route • Acidity/Alkalinity • Absorption relates to bioavailability • The amount of the drug that reaches the bloodstream and/or site of action

  6. Distribution • Refers to a drug’s ability to reach a wide range of tissues • Solubility – Lipid solubility. Highly lipid soluble = greater distribution and effect. • Blood Brain Barrier • Depot binding: Drug binding to inactive sites • Fat, Protein, Muscle • THC testing

  7. Blood-brain barrier limits drug access to brain

  8. Biotransformation • Drug Metabolization – Mainly in LIVER • Many drugs are broken down into other compounds. Some are not transformed at all • Enzymes break down drugs into metabolites • Drugs that use the same enzyme interact • Metabolites can be active or inactive • Metabolization occurs in an ordered manner • Half-life – The amount of time it takes for drug plasma level to be reduced by half • THC – 20 hours – 9 days • Cocaine – 45 minutes • Zoloft 2-3 days Prozac 7-9 days

  9. Drug Elimination • Drugs are excreted in a variety of ways • Urine • Breath • Feces • Sweat • Can be excreted changed or unchanged (alcohol vs. psylocibin)

  10. Target - Receptor Depot – Bone & Fat Blood Plasma Excretion Intestines, Kidneys, Lungs, etc. Absorption & Distribution Plasma Protein Binding Metabolites Administration Oral, IV, IM, IP, SC, Inhalation, TC Feces, Urine, Sweat, Saliva Liver

  11. Pharmacodynamics • Interaction between the drug and the target tissue • For psychoactive drugs target tissues are receptors in CNS • General Terms • Receptor • Site of initial interaction • Ligand • Any molecule that binds to a receptor • Agonists • Increases NT for a transmitter system • Antagonists • Decreases NT for a transmitter system

  12. Receptors • IONOTROPIC • Work rapidly. Involved in “fast” NT • Ion channels open when NT occupies • Sodium • Calcium • Chloride • METABOTROPIC • Slower, longer lasting • Work through a “second messenger”

  13. Agonist/Antagonist • Agonist • Drug binds and induces full pharmacological effect • Partial Agonist • Drug binds and exerts only a partial effect • Competitive Antagonist • Binds to same receptor as agonist • Reduces the effect • Effect can be overcome by sufficient dose • Noncompetitive Antagonist • Binds in other ways, but disrupts agonist binding • Reduces the effect • Effect can not be overcome by sufficient dose

  14. Forms of Drug Action at the Synapse • Ways to agonize • Stimulate release • Receptor binding • Inhibition of reuptake • Inhibition of deactivation • Promote synthesis • Ways antagonize • Block release • Receptor blocker • Prevent synthesis 8. Autoreceptors

  15. Acetylcholine Agonists Nicotine Physostigmine Antagonists Muscarinic receptor - Atropine Nicotinic receptor - Curare

  16. GABA • Valium, Xanax, Ativan • Act as GABA agonists • GHB, Rohypnol • GABA agonist

  17. Dopamine • Cocaine • dopamine reuptake inhibitor • Amphetamine • increases DA release • Antipsychotics • block post-synaptic dopamine receptor

  18. Serotonin • Selective-serotonin reuptake inhibitors (SSRIs) – used to treat depression

  19. Dose Issues

  20. General Drug Effects • Main Effect – The reason why the drug is taken • This may be therapeutic or recreational • Side Effects – All effects other than the main effect • One person’s side-effect is another person’s main effect. • Ultimately drugs have an effect, we label it base on need or context.

  21. Dose Response Curve Dose-Response Curve • Plots the relation between the dose of the drug and the size of the effect • Specific to the behavior you are measuring • Drugs have multiple effects and curves

  22. DRC Characteristics • Slope • gradual versus steep • Potency • amount required to produce effect • Maximum efficacy • upper end where response levels out % of Maximal Effect Drug Dose

  23. Effective vs. Lethal Dose • Effective Dose(ED) • Dose level for chosen effect in % of population • ED50, dose in which drug is effective for 50% of population • Lethal Dose (LD) • Dose level for death in % of population • LD50 = lethal dose for 50% of the population • Therapeutic Index • LD50/ED50 - Serves as margin of drug’s safety • Higher ratio  more safe/less toxic • 20 or more = relatively safe, 100 preferred

  24. Drug Interactions • Using multiple drugs increases the complexity of the experience • Antagonism – One drug inhibits the effect of another drug • Cocaine and alcohol (Pharmacodynamic) • St. John’s Wort and Birth Control Pills (Pharmacokinetic) • Potentiation – The two drugs together produced and enhanced effect • Alcohol and nicotine

  25. Street “dynamics” • Reality is that with illicit drugs, pharmacodynamics is ignored • Most drugs are diluted • Changes ED • Most are “cut” with dangerous compounds • Changes LD • Sometimes dose is too high, leading to acute toxicity • Potentiation and Antagonism work here

  26. Tolerance Sensitization Dependence and Withdrawal Issues of Repeated Use

  27. Decreased response to drug with repeated use Shifting DRC to the right 3 types Metabolic Liver enzymes Cellular Receptor down-regulation Learned Context/cues Acute vs. Protracted Acute is within a single administration Cross-tolerance Tolerance to one drug leads to tolerance of other drugs in the same class. Tolerance

  28. Sensitization • Increased response to a drug with repeated use • Shifting DRC to the left • Cocaine-induced, movement, cataplexy and seizures • Cocaine is a good example of a drug induces tolerance (euphoria) and sensitization (movement)

  29. Repeated Self-Administration • Mesolimbic dopamine system • Abused drugs all tend to activate this system • 3 stages • Pleasure • Associative learning through classical conditioning • Incentive salience • Craving (wanting) • Get DA release by cues/context alone

  30. Dependence/Withdrawal • Physiological Dependence • Body adapts to presence of drug. Needs drug on board to maintain homeostasis • Indicated by the display of withdrawal symptoms upon cessation of drug use • Withdrawal symptoms • Behaviors displayed by a user when drug use ends • Typically the opposite of the drug effect

  31. Behavioral Pharmacology

  32. Behavioral Pharmacology • Study of the relationship between the physiological actions of drugs and their effects on behavior and psychological function • Drugs do not create behaviors outside the normal species-typical repertoire • They alter the probability or form of behaviors • Uses the principles of operant and classical conditioning to examine the effects of drugs as well as the differences and similarities between drugs • Self-administration studies • Discrimination studies • Conditioned place preference studies • Conflict paradigm studies

  33. Self-administration • Train animal to press lever for drug administration • All drugs shown to be SA by animals are SA by humans • Alcohol • Cocaine • THC

  34. Drug Discrimination Drugs can serve as discriminative stimuli • Animals learn to respond in certain ways in the presence of a drug • Discrimination is related to interoceptive cue • Using these techniques, it appears that animals classify drugs just like humans • Amphetamine and cocaine alike, but different from morphine, while morphine is like heroin and other opiates Method to ask animals about the interoceptive cues associated with different drugs Press left lever if on morphine > get food Right lever if given saline > get food Give new drug - is it like morphine? • Left lever - Yes • Right lever - No

  35. Conditioned Place Preference • Pair drug administration with a place in the environment • Give animal a choice of where to hang out. • Measure where animal spends time

  36. Conflict Paradigm • Train animal to associate both reinforcement and punishment with a certain behavior • Food and shock w/lever press • Administer a drug to test effects • Xanax

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