Pharmacology (Repeat and New Info.)

jasmine's version from 2015-10-18 15:49

Section 1

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PinocytosisMost common way drugs cross a cell membrane; It is a process by which cells carry a drug across their membrane by engulfing the drug particles
Channels and Pores Very few drugs cross through by this way due to the membranes being extremely small, specific for certain molecules, and if direct area is right
Transport Systems Selective carriers that can move drugs from one side of the cell membrane to the other, and may or may not require the expenditure of energy; Without these, certain orally administered drugs could not be absorbed; A number of drugs could not reach intracellular sites of action; Renal excretion of many drugs would be extremely slow, as these are in the kidney and pump drugs from the blood into renal tubules
P-Glycoprotein Transporter known as multidrug transporter protein; It is a transmembrane protein that transports a wide variety of drugs out of the cells
P-Glycoprotein in Liver Transports drugs into the bile for elimination
P-Glycoprotein in Kidney Pumps drugs into the urine for excretion
P-Glycoprotein in Placenta Transports drugs back into the maternal blood, thereby reducing fetal drug exposure
P-Glycoprotein in Intestine Transports drugs into the intestinal lumen, and can thereby reduce drug absorption into the blood
P-Glycoprotein in Brain Capillaries Pumps drugs into the blood, thereby limiting drug access to the brain
General Rule in Chemistry like dissolves like; For example, polar molecules will dissolve in polar solvents yet in not non-polar solvents; Except for very small molecules, ions are unable to cross membranes; Quaternary Ammonium Compounds always carry a positive charge, hence unable to cross membranes
Many Drugs are Either Weak organic acids or weak organic bases, which can exist in charged or uncharged forms to be determined by the pH of the surrounding medium
Acid Proton donor, and tends to ionize in basic (alkaline media); charged particle (ion)-ionization process; Acidic drugs will accumulate on the alkaline side (ion trapping or pH partitioning)
Base Proton acceptor, and tends to ionize in acidic media; charged particle (ion)-ionization process; Basic drugs will accumulate on the acidic side (ion trapping or pH partitioning)
Ion Trapping Causes Molecules such as Orally Administered Aspirin to... Move from the acidic (pH 1) environment of the stomach to the more alkaline (pH 7.4) environment of the plasma, thereby causing aspirin to accumulate in the blood; Some molecules give up a proton and become ionized, however most in the stomach remains non-ionized due to the stomach being acidic and acidic drugs do not ionize in acidic media; Most molecules in the stomach are non-ionized (lipid soluble) most in the stomach can readily cross the membranes and move into the plasma to where most give up a proton. Laws of diffusion: The concentration of ASA molecules in the plasma will be much higher than in the stomach
Factors Affecting Drug Absorption Rate of dissolution (i.e., rapid dissolution has faster onset), surface area (i.e., intestine has larger surface area than stomach and will therefore absorb faster), blood flow (drugs absorbed more quickly where blood flow is high), lipid solubility (i.e., drugs absorbed more quickly where lipid solubility is higher), and pH partitioning, or ion trapping (Enhanced when the difference between pH of plasma and the pH at the site of administration is such that drug molecules will have a greater tendency to be ionized in the plasma)
2 Major Groups of Administration Used Most Commonly Enteral (PO; the gastrointestinal tract), and parenteral (injection)
Simply giving the right drug is not sufficient; what must also be considered? The formulation and concentration are appropriate for the route (i.e., whereas insulin solutions intended for subcutaneous administration are concentrated, solutions intended for intravenous use are dilute; subcutaneous insulin solutions administered through intravenous route can result in death)
Depot Preparations Drug is absorbed slowly over an extended time, hence can greatly reduce the number of injections required during long-term therapy
Movement of Drugs Following gastrointestinal absorption (stomach, small and large intestine), the drug must go through the liver, via the portal vein, on its way to the heart and then the general circulation; Other undergo extensive hepatic metabolism, and still others undergo enterohepatic recirculation, a repeating cycle in which a drug moves from the liver into the duodenum (via the bile duct) and then back to the liver (via the portal blood), however the process is limited to drugs that have first undergone hepatic glucuronidation
Oral Administration is the Preferred Route Due to No risk of fluid overload, infection, or embolism, to include the ability to prevent the absorption of drugs by way of activated charcoal, a factor unavailable with drugs given by injection
Activated Charcoal A compound that absorbs (soaks up) drugs while they are still in the GI tract; once the drugs are absorbed, they cannot be absorbed into the blood stream
First-Pass Effect Drugs such as nitroglycerin that undergo extensive inactivation as they pass through the liver is a phenomenon known as this
BioavailibilityA subcategory of absorption; It is the percentage of the administered drug dose that reaches the systemic circulation.
Factors That Affect BioavailibilityBioavailibility: the drug form, the route, GI mucosa and motility, food and other drugs and changes in liver metabolism
First-Pass EffectThe process in which the drug passes to the liver first; Example: Wafrarin and morphine
Chemical Equivalence Drug preparations are considered this if they contain the same amount of the identical chemical compound (drug)
Other Definition for Bio-availabilityPreparations are considered equal in this if the drug they contain is absorbed at the same rate and to the same extent
Important It is possible for two formulations of the same drug to be chemically equivalent while differing in bioavailability
Tablets made by different manufacturers can differ by... its rates of disintegration and dissolution, causing differences in bioavailability; As a result, two tablets that contain the same amount of the same drug can differ with respect to onset and intensity of effects
Creatinine ClearanceMost accurate test to determine renal function; It is used to estimate glomerular filtration rate (GFR). GFR is a measure of how well the kidneys are working, especially the kidneys' filtering units. These filtering units are called glomeruli.
Half-LifeThe time it takes for one half of the drug concentration to be eliminated; A drug goes through several of these before 90 percent of the drug is eliminated
Time-Response CurveEvaluates 3 parameters of drug action; the onset of drug action, peak action and duration of action
Onset Of Action The time it takes to reach the minimum effective concentration (MEC) after a drug is administered
Peak ActionOccurs when the drug reaches its highest blood or plasma concentration
Peak Drug LevelThe highest plasma concentration of drug at a specific time; indicates rate of absorption
Duration Of ActionThe length of time of the drug as a pharmacologic effect
Trough Drug LevelThe lowest plasma concentration of a drug and it measures the rate at which the drug has been eliminated
Therapeutic Range (window)The drug concentration that is between the minimum effective concentration in the plasma for obtaining desired drug action and the minimum toxic concentration
Maximal EfficacyPart of the pharmacodynamic phase; The maximum drug effect; Example: Morphine prescribed for pain relief. The maximum efficacy of morphine is greater than that of Tylenol (regardless of how much Tylenol is given)

Section 2

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Section 3

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