Intro To Pharmacology

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Pharmacology

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study of drugs, interactions with living systems, understanding physical, chemical properties, effects in the body, use of drugs, understanding how drugs are absorbed, distributed, metabolized and excreted.

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Clinical Pharmacology

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study of drugs in humans

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Therapuetics

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Pharmacotherapeutics): use of drugs to diagnose, prevent or treat disease, medical use.

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Drug Names

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1. Chemical name: chemical description

2. Generic name: non-proprietary name, given by United States Adopted Name Council.

3. Trade name: proprietary, created by drug companies, name approved by the FDA.

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Major Properties of an Ideal Drug

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1. Effectiveness: elicits the intended response.

2. Safety: does not produce harmful effects.

3. Selectivity: produces only the response for which it is given.

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Therapeutic Objective

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Provide maximum benefit with minimum harm.

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Factors Determining the Intensity of Drug Responses

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1. Administration: drug dosage, route of administration, timing of administration.

2. Pharmacokinetics: how the body affects the drug. Four pharmacokinetic processes: absorption, distribution, metabolism and excretion.

3. Pharmacodynamics: how the drug affects the body. Pharmacodynamic processes involve drug-receptor binding followed by the events that lead to the response.

4. Individual Variation:
a. physiological factors
b. pathophysiology
c. genetic factors

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Pharmacokinetics

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1. Absorption: mov’t of the drug from its site of administration into blood
2. Distribution: drug mov’t from blood to interstitial space of tissue and into the cells.
3. Metabolism: enzymatic processes that alter the drug
4. Excretion: movement of drug and metabolites out of the body.

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Drug Transport Across Cell Membranes

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1. Direct penetration: crosses membrane by penetrating through it. Lipid soluble.

2. Transport systems: carry the drug across the membrane. Selective. P-glycoprotein - transports drugs out of cells

3. Passage through channels and pores: very small to pass through.

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Absorption

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Mov’t of drug from its site of administration into the blood.

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Bioavailability

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extent to which a drug is absorbed and transported to the target tissue.

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Factors that affect drug absorption

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a. rate of dissolution: how easily drug dissolves. dissolves easy = quicker absorption.

b. surface area: the larger the surface area the quicker the drug will be absorbed.

c. blood flow: absorbed quicker from sites with high blood flow

d. lipid solubility: drugs with high lipid solubility are absorbed quicker

e. pH partitioning: difference in the pH of the plasma and pH at the site of admin, greater the difference the more easily absorbed.

f. site of absorption: absorption vary depending on the site of admin, route.

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Routes of Administration

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a. intravenous: administered directly into the blood stream

b. intramuscular: injection into muscle, easily absorbed

c. subcutaneous: injection into subcutaneous tissue.

d. oral: absorbed from the stomach or the intestine. Barrier to absorption is the epithelial cells, transporter P-glycoprotein

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Advantages/Disadvantages of Intravenous

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advantages: rapid onset, tight control over drug levels, can use large am’t of fluid disadvantages: dangerous – too fast, can’t take it back, inc risk of infection, cost

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Advantages/Disadvantages of Intramuscular/Subcutaneous

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advantages: used for meds that do not dissolve well, depot prep
disadvantages: painful, damage to local tissue, nerve damage.

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Oral absorption influenced by

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1. food or delayed gastric emptying
2. drug interactions
3. coating
4. solubility of the drug, pH

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Advantages/Disadvantages of Oral

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advantages: convenient, easier to use, less expensive.
disadvantags: inactivation or destruction of the drug, GI irritation, absorption variable from pt to pt.

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Oral formulations

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1. tablets: mixture of drug plus binders and fillers

2. enteric-coated preparations: coated so will dissolve in intestines but not stomach. The coating protects drug or protect the stomach

3. sustained release preparations: capsules filled with coated spheres that contain the drug. coatings dissolve at variable rates

e. other: topical – applied to the skin, eyes, nose, ears, vaginally, rectally, inhalation

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Distribution

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Mov’t of drugs through the body
1. blood flow to the tissues: Drugs delivered by blood stream and rate of delivery determined by blood

2. ability of drug to exit the vascular system: exit at the capillary beds, easily pass between capillary cells except at:
a. blood brain barrier: protects the brain from toxic substances. tight junctions between the capillary cells so through the cells – lipid soluble, med with transport system

b. placenta: protective barrier. lipid soluble can pass

3. ability of drug to enter cells: lipid solubility and the presence of a transport system. some drugs do not cross cell membrane – bind with receptors.

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Metabolism

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enzymatic alteration of the drug – referred to as the biotransformation. Occurs in the liver – the hepatic microsomal enzyme system. P450 system

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Effects of Drug Metabolism

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a. accelerated renal drug excretion: unable to excrete lipid soluble drugs, metabolism converts lipid soluble drugs into compounds easier to excrete.

b. drug inactivation: convert active compounds to inactive forms
c. inc. therapeutic action: inc effectiveness of some drugs by converting into more active form

d. activation of drugs: inactive compound (prodrug) into an active form.

e. inc. or dec. toxicity: dec. in toxicity occur when drug converted into inactive form. Inc. occur when drugs transformed into toxic substances.

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Factors that influence Metabolism

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a. age: infants sensitive to drugs until liver matures

b. induction of drug metabolizing enzymes: drugs cause liver to produce drug-metabolizing enzymes through induction. Induction inc metabolism of drugs -> inc doses needed to maintain therapeutic levels.

c. first-pass effect: rapid hepatic inactivation of a drug. To prevent use other routes than po.

d. nutrition: Cofactors needed for metabolism.
e. drug competition: compete with each other for metabolism if use

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Steps in Drug Excretion

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a. glomerular filtration: All drugs except those bound to albumin are filtered through the glomerular membrane.

b. passive tubular reabsorption: lipid-soluble drugs reabsorbed into the blood. Non-lipid soluble drugs (ions, polar) remain in the tubules and excreted in the urine.

c. active tubular secretion: Active transport systems pump drugs from blood into the urine. P-glycoprotein, pumps for organic acids/bases

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Factors that Affect Renal Drug Excretion

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a. pH dependent ionization: can speed up excretion of drugs. Changing pH of the urine causes ionization of drugs - reabsorption dec, excretion inc.

b. competition for active tubular transport: competition can delay excretion and prolong the effects of the drug.

c. age: infants kidneys not fully developed. Elderly – decline in renal function

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Plasma Drug Levels

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to regulate drug responses. Adjust up or down.

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MEC

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minimum concentration that is effective – anything below it is not effective.

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Toxic concentration

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toxicity occurs

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Half-Life

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time required for amount of drug in body to dec by 50%. Drugs with short half-lives = excreted quickly, long half-lives = excreted more slowly. Half-life determines dosing interval – the time between doses. Long half-life = long time between doses. Short half life = interval between doses shorter

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single dosing

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plasma levels go up as drug is absorbed. Drug therapeutic at MEC then it will be therapeutic. Plasma levels dec when metabolized and excreted.

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multiple dosing

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accumulation of drug in the body

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plateau

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drug level constant – 4 half lives

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loading dose

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big dose to get their therapeutic level up quickly

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maintenance dose

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to keep them at therapeutic level

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peak

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highest level of drug

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trough

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above minimum therapeutic level