Textbook Notes (368,338)
Canada (161,803)
Psychology (9,695)
PSYC62H3 (313)
Chapter 3

Chapter 3.docx

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Suzanne Erb

CHAPTER 3: BASIC PRINCIPLES OF PHARMACOLOGY -psychological effects of a drug at an particular time depend on: individuals set & setting, particular way the drug changes activities in the CNS, the route of administration of the drug, the amount of the drug administered & the frequency with which it is administered -word drug = no commonly accepted definition -originally referred to any substance used in chemistry or medical practice -gradually restricted to any agent used in medicine or any ingredient in medicines -today used as synonym for a narcotic agent or illicit substance -in general its a chemical that affects one or more biological processes BUT not all chemicals that affect biological processes = drugs i.e. salt, water, proteins, fats, carbs, vitamins & mineralsSt. Johns Wort =antidepressant Endogenous substances- chemicals originating or produces within an organism that are used to carry out normal biological functions in the body arent usually though as drugs opposed to drugs which are exogenous Drug: non-food, nonmechanical substance (usually chemical substance) that exerts an effect upon a living system BASIC CHEMICAL PRINCIPLES RELATED TO PSYCHOPHARMACOLOGY - lipid bilayer provides a barrier to the movement of any polar & charge substances -any drug that is highly lipid-soluble would easily be stored In adipose tissue & if it is not metabolized it could stay there for a long time -cell membrane (which is made up mostly of a lipid-bilayer) would present a barrier to diffusion of any substance that is too water-soluble i.e. lipophobic & not transported across the membrane by proteins -stomach & intestines are lined with cells & if a pill is introduced into the body this would represent the first barrier to entry into systemic circulation -additional barriers in the circulatory system & metabolic enzymes in the liver -most drugs must pass into the brain -significant barrier in the brain = BBB: made up of tight junctions between endothelial cells that compose the outer lining of the blood vessels -barrier can provide significant resistance to the entry of drugs & other substances in the brain & subtle alterations in the chemical structure of drugs can yield substantial differences in passage across the BBB i.e. scopolamine & atropine readily penetrate into the brain to produce therapeutic effects but two close structural analogs of these drugs i.e. methylscopolamine & methylatropine = additional positive charge = more water soluble & less likely to readily penetrate into the brain -ethanol soluble in both water & lipid, easily passes from stomach to circulatory system, dissolves in blood & easily passes into brain; metabolized by enzymes at 1ounce/hr & metabolites = water-soluble & removed in urine -9 THC mostly hydrocarbon .:. highly lipid-soluble, rapidly absorbed when smoked & easily passes through BBB BUT not rapidly metabolized & is very water-soluble so deposits itself in adipose tissue for ~several weeks -examples of importance of water vs. lipid solubility for drug distribution/action i.e. differences in onset, intensity & duration; low lipid solubility (morphine) = slower onset of analgesia & less intensity but longer duration Pharmacokinetics: dynamic processes involved in the movement of drugs within biological systems with respect to the drugs absorption, distribution, binding or localization in tissues, metabolic alteration & excretion from the body Pharmacodynamics: biochemical & physiological effects of drugs & their mechanisms of action ROUTES OF ADMINISTRATION -most common route of drug administration is through the mouth so that the drug is absorbed in various parts of the gastrointestinal tract -rectal administration (through rectal mucosa) may serve as an alternative enteral (within the intestine) route for drugs destroyed in the stomach/small intestine -PO route is generally safest, cheapest & most convenient way of administrating drugs -several factors influence the absorption of drugs from the GI tract which effects the rate of drug accumulation, concentration & duration -most drugs are through to penetrate the GI mucosa by process of passive diffusionlimited to mostly by lipid solubility -many drugs = weak bases/acids = ionized: state which atom/molecule has a net electrical charge-bc proteins embedded in these membranes have mixture of positive/negative charges that tend to repel charged particles, ionization reduces solubility -to facilitate their absorption such drugs are commonly administrated in form of salt -the pH of the local area determines the ratio of ionized to nonionized drug in that area i.e. weak acids (Aspirin) are less ionized in an acid medium & therefore more lipid-soluble through stomach with ph < 3.0 i.e. weak bases (Heroin) poorly absorbed from stomach but in small intestine, where contents = neutral/basic the environment favours absorption of weak bases Intravenous (IV) injection: a drug directly into the blood results in rapid onset of drug action & relatively intense effects -time takes for drug to circulate b/w vein of forearm -> brain <15s -fine adjustments in drug dosage possible BUT if overdosage does occur, little can be done unless antagonist for drug available -must be in solution/microsuspension & must have an aqueous vehicle Intramuscular (IM) injection: results in a more rapid absorption than PO route bc of good blood supply around muscles -drugs dissolved in aqueous vehicle are more rapidly absorbed through IM route than when dissolved/suspended in oil -because the lining of the inside of the lungs provides a large surface area close to blood vessels drug inhalation leads to rapid onset of drug action & intense effects -this route eliminates drug loss through first-pass metabolism by the liver -irritates/oil can cause pneumonia & long-term consequences i.e. cancer w/ cigarette smoking occur in route Subcutaneous (SC) injection: injection of a drug underneath the skin into the tissue bw the skin & muscle i.e. into the body fat -relatively poor blood supply in fatty tissue .:. used w. nonirritating substances = slow & even absorption -rate of absorption controlled through form of the drug -aqueous solution = fast absorption; suspension = ~ slower absorption; solid form = very slow absorption Sublingual or buccal administration: through oral mucosa under the tongue or
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