Pharm Exam 1 Things To Know

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Pharmacology

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Pharmakon = greek for poison

Study of drugs and their interactions with living systems.

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Theraputic Objective

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Provide maximum benefit with minimun harm.

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Pharmacotheraputics

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Use of drugs to diagnose, treat, or prevent disease, medical use.

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Drug Names:
(1) Chemical
(2) Trade
(3) Generic

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(1) Chemical description.
(2) Proprietary name, created by drug companies, approved by FDA, many names
(3) Non-Proprietary name, given by USANC, only one name

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3 Major properties of an ideal drug

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(1) Efficacy
(2) Safety
(3) Selectivity

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Drug Efficacy

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The most important property a drug can have. An effective drug is one that elicits the responses for which it is given.

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Drug Safety

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A safe drug is one that cannot produce harmful effects-even if administered for a long time. No such thing. Only degrees of safety.

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Drug selectivity

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A selective drug is one that elicits the only response for which it is given. No such thing because all meds cause side effects.

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Factors determining the intensity of drug responsivness
(When administering a drug the ultimate concern is the intensity of the response)

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(1) Administration
(2) Pharmacokinetics
(3) Pharmacodynamics
(4) Individual variation

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Administration

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Dosage size, route, and timing of administration are important determinants of drug response.

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Pharmacokinetics

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How the body affects the drug. Four processes
(1) Drug adsorption
(2) Drug distribution
(3) Drug metabolism
(4) Drug excretion

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Pharmacodynamics

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How the drug affects the body. Pharmacodynamic processes involve drug-receptor binding and the events that follow leading to a response.

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Individual variation

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Physiological factors
-age, gender, weight
(2) Pathological factors
-renal or hepatic dysfunction
(3) Genetic Factors
-predisposition, allergy, etc.

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Adherence

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Compliance or concordance. The extent to which a patients behavior coincides with medical advice. To reach the objective, this is essential.

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Drug transport across cell membranes:
3 processes involved in each of the pharmacokinetic phases

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(1) Direct penetration – drug crosses membrane by penetrating through it. Lipid soluble drugs only. (Rem: phospholipid bi-layer) Most common.
(2) Transport systems – selective carriers that move drugs from one side of the membrane to the other. P-glycoprotein transports a variety of drugs out of cells aiding excretion, preventing drug access to the brain, and reducing drug adsorption in the intestine.
(3) Passage through channels or pores – very limited due to the small size of these passageways, most drugs are too large. Only low molecular weight drugs or small ions like K+ or Na+.

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Adsorption

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The movement of drugs from the administration site into the blood. The rate of adsorption determines how soon the effect will begin. The amount of adsorption helps determine how intense effects will be.

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Factors that affect drug adsorption

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(1) Rate of dissolution – to be adsorbed, it first must dissolve. Therefore this rate determines the rate of adsorption. = Quick dissolution => Quick adsorption => Quick onset.
(2) Surface area – the available surface area determines rate of adsorption. More area => Faster adsorption. This is why most oral drugs are absorbed in the intestine rather than the stomach.
(3) Blood flow – drugs are absorbed rapidly from sites where blood flow is high because the drug filled blood will be replaced by new blood and maintain a steep concentration gradient. The higher the concentration gradient, the faster the adsorption to equalize it.

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Factors that affect drug adsorption, cont.

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(4) Lipid solubility – lipid soluble drugs are absorbed faster since they can directly penetrate the cell membranes that separate them from the blood.
(5) PH partitioning – adsorption will be enhanced when the difference between the pH of the plasma and the pH at the site of drug admin is such that drug molecules will have a greater tendency to be ionized in the plasma.
(6) Site of adsorption – variation will occur based on route of admin and site of admin.

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Bioavailability

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

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Routes of administration

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IV- intrvenous- administered directly into the blood stream- no barrier to adsorption = rapid onset
IM- intramuscular- injected into the tissue of certain muscles, no signifcicant barriers to adsorption, which can be fast or slow
SubQ- sub-cutaneous- administered under skin, not into muscle tissue.
PO- oral- administration through the mouth, epithelial cells do pose as barriers to adsorption
Other- topical, rectal, otic, optic, etc.

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Adsorption, Advantages and disadvantages of IV administration

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Advantages- because adsorption is immediate and complete, rapid onset, tight control of drug levels, can use a large amount of fluid
Disadvantages- due to instantaneous absorption and rapid onset, it is dangerous, and irreversible, costly, can be inconvenient, increase risk of infection.

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Adsorption, Advantages and disadvantages of IM administration

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IM meds will be absorbed quickly if they are water soluble and/or if there is good blood flow to the injection site.
Advantages- great to admin poorly soluble drugs or depot prep drugs that allow slow adsorption over time reducing # of admins necessary.
Disadvantages- discomfort or pain, inconveience, can damage local tissue and nerves.

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Adsorption, Advantages and disadvantages of subcutaneous administration

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Similar pharmacokinetics to IM administration and therefore similar advantages and disadvantages.

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Adsorption, Advantages and disadvantages of oral administration

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Adsorption is done in the stomach or the small intestine. Epithelial cells in the GI tract and capillary walls must be cross by the drug. This can be inhibited even further by P-glycoprotein.
Absorption influenced by:
1. food or delayed gastric emptying
2. drug interactions
3. coating
4. solubility of the drug, pH
Advantages- cheap, easy, convenient.
Disadvantages- variability between patients, inactivation within the GI tract, local irritation

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Oral drug formulations

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(1) tablets - mixture of drug and fillers or binders.
(2) enteric coated tablets- coated to dissolve in the intestine, not the stomach. The coating protects the drug and the stomach.

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Distribution

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The movement of drugs throughout the body. Is determined by 3 factors.

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3 Factors that affect distribution

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(1) Blood flow to tissues- blood carries drugs to the tissues and organs. Determines rate of distribution. Regional blood flow is very rarely a factor, except when abcesses or tumors are present.
(2)Ability of drug to exit the vasculature- This step is important in determining the action of drugs, since most do not produce their effect from within the blood. Their exit is also necessary for metabolism and excretion.Drugs leave the blood at the capillary bed, between cells not through them.
(3) Ability of drug to enter cells- prescence of a transport system, lipid solubilty, or both.

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Unique capillary bed considerations in distribution

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Blood-brain barrier- referes to the cappilary structure in the brain that has tight junctions between cells that prevent the passage of CNS drugs between them. Also presence of P-glycoprotein protects the brain. Lipid soluble and meds with transport system can pass.
Placenta- a protective barrier, but is not absolute. Lipid soluble can pass.

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Metabolism

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AKA biotransformation, is the enzymatic alteration of drug structure. Most drug metabolism takes place in the liver. This happens through the hepatic microsomal enzyme system, or the P450 system.