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Flashcards in Intro to Clinical Pharmacology Deck (62):
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Drug

Any chemical that can affect living processes

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Pharmacology

The study of drugs and their interaction in living systems

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Clinical pharmacology

Study of drugs in humans

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Therapeutics

Use of drugs to diagnose, prevent, and treat disease or to prevent pregnancy

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Properties of an Ideal Drug

-Effectiveness: elicit the responses for which it is given
-Safety: drug cannot produce harmful effects
-Selectivity: elicits only the response for which it is given

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Factors that determine the intensity of drug responses

Administration, pharmacokinetics, pharmacodynamics, sources of individual variation

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Pharmacokinetics

Impact of body on the drugs; absorption, distribution, metabolism, excretion, time course of drug responses

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Application of pharmacokinetics in therapeutics

By applying knowledge of pharmacokinetics to drug therapy, we can help maximize beneficial effects and minimize harm

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Absorption

Movement of a drug from its site of administration into the blood

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Rate of absorption

Determines how soon effects will begin

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Amount of absorption

Helps determine how intense the effects will be

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Factors affecting drug absorption

Rate of dissolution, surface area, blood flow, lipid solubility, pH partitioning

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Distribution

Movement of drugs throughout the body

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How is drug distribution determined? (3 factors)

-Blood flow to tissues
-Exiting the vascular system
-Entering cells

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Blood Flow to Tissues

-Drugs are carried by the blood to tissues and organs of the body
-Blood flow determines rate of delivery

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Abscesses and tumors (reg. blood flow to tissues)

-Low regional blood flow impacts therapy
-Pus-filled pockets, not internal blood vessels
-Solid tumors have limited blood supply

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Blood-Brain Barrier (BBB)

Tight junction between the cells that compose the walls of most capillaries in the CNS
-Drugs must be able to pass through cells of the capillary wall; only drugs that are lipid soluble or have a transport system can cross the BBB to a significant degree

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Placental Drug Transfer

Membranes of the placenta do NOT constitute an absolute barrier to the passage of drugs; movement determined in the same way as other membranes

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Risk with placental drug transfer

Birth defects: mental retardation, gross malformations, low birth weight; mother's use of habitual opioids: birth of drug-dependent baby

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Protein Binding

Drugs can form reversible bonds with various proteins; Plasma albumin is the most abundant and important > large molecule that always remains in the bloodstream; impacts drug distribution

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Entering cells

-Some drugs must enter cells to reach the side of action
-Most drugs must enter cells to undergo metabolism and excretion
-Many drugs produce their effects by binding with receptors on the external surface of the cell membrane > do not need to cross the cell membrane to act

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Drug Metabolism

Biotransformation; the enzymatic alteration of drug structure > most often takes place in the liver

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P450 System

Most drug metabolism that takes place in the liver is performed by the hepatic microsomal enzyme system; metabolism doesn't always result in a smaller molecule

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Special Considerations in Drug Metabolism

Age, induction of drug-metabolizing enzymes, first-pass effect, nutritional status, competition between drugs

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Excretion

Removal of drugs from the body; drugs and their metabolites can exit the body through urine, sweat, saliva, breast milk, or expired air

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Renal routes of drug excretion

Glomerular filtration, passive tubular reabsorption, active tubular secretion (kidneys)

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Factors that modify renal drug exretion

pH-dependent ionization, competition for active tubular transport, age

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Nonrenal routes of drug excretion

Breast milk, bile, lungs (especially anesthesia), sweat/saliva

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Pharmacodynamics

Study of biochemical and physiologic effects of drugs and the molecular mechanisms by which those effects are produced; study of what drugs do to the body and how they do it

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Sources of individual variation

Physiologic variables (age, gender, weight)
Pathologic variables (diminished renal and liver function)
Genetic variables (can alter drug metabolism)
Drug interactions (no two patients alike)

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Half life

Time required for the amount of drug in the body to decrease by 50%; determines the dosing interval

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Controlled Substance Act (Landmark Drug Legislation)

Established categories into which controlled substances are placed; Schedule I-V

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Schedule I drugs

No accepted use in US and have high potential for addiction (ie. heroin, LSD, cigarette marijuana)

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Schedule II drugs

Accepted medical use, high abuse potential; written prescription needed/no refills allowed (ie. dilaudid, cocaine, dura morph, codeine)

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Schedule III drugs

Medical use, less abuse potential (ie. marinol, vicodin)

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Schedule IV drugs

Phenobaritol, ambien, lorazepam

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Schedule V drugs

Lomotil, robitussin AC (codeine)

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New Drug Development

Pre-clinical testing (animal testing): toxicity, pharmacokinetics, useful effects
Clinical testing (2-10 years)
-Phase I: healthy volunteers (check toxicity)
-Phase II/III: patients (on sick patients, adverse effects)
-Phase IV: Aftermarket surveillance (once drug has been approved)

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Drug Names

Chemical, generic (nonproprietary), trade (brand)

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Consequences of drug-drug interactions

Intensified effects, increased therapeutic effects, increased adverse effects

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Basic mechanisms of drug-drug interactions

Direct chemical or physical interaction; pharmacokinetic interactions: altered absorption, altered distribution, altered metabolism, altered renal excretion, interactions that involve P-glycoprotein

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Ways to reduce medication errors

Replace handwritten medication orders with a computerized order entry system; have a senior clinical pharmacist accompany physicians on rounds; use a bar-code system

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Individual variation in drug responses

Gender, race, failure to take medicine as prescribed, drug interaction, diet

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Efficacy

Maximum effect that a drug can produce, regardless of dose

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Potency

Amount of a drug tat is needed to produce a given effect

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Drugs

Chemicals that produce effects by interacting with other chemicals

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Receptors

Special chemicals in the body that most drugs interact with to produce effects

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Important properties of receptors

-Receptors are normal points of control of physiologic processes
-Under physiologic conditions, receptor function is regulated by molecules supplied by the body
-Drugs can only mimic or block the body's own regulatory molecules
-Drugs cannot give cells new functions

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Agonists

Molecules that activate receptors

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Antagonists

Preventing receptor activation; noncompetitive and competitive

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Partial agonists

Agonists that only have a moderate intrinsic activity; maximal effect that a partial agonist can produce is less than that of a full agonist. Can act as antagonists as well as agonists

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Noncompetitive antagonists

Bind irreversibly to receptors, reduce the maximal response that an agonist can elicit, impact not permanent

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Competitive antagonists

Compete with agonists for receptor binding, bind reversibly to receptors; equal affinity: receptor occupied by whichever agent is present in the highest concentration

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Interpatient variability in drug responses

Initial dose of a drug is necessarily an approximation, subsequent doses must be "fine tuned" based on the patient's response

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ED50

Effective dose in 50% of the population tested

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LD50

Average lethal dose to 50% of the animals treated

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Therapeutic Index

Measure of drug's safety; ratio of drug's LD50 to its ED50. Higher the therapeutic index, the safer the drug; lower the therapeutic index, less safe the drug

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Drug-drug interations

Interactions occur whenever a patient takes more than one drug; some are intended and others are undesired

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Consequences of drug-drug interactions

Intensification of effects (increased therapeutic/adverse effects), reduction of effects, creation of a unique response

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Clinical significance of drug-drug interactions

-Potential to significantly impact the outcome of therapy
-Responses may be increased or reduced
-Risk for serious drug interaction is directly proportionate to the number of drugs a patient is taking
-Interactions are especially important in drugs w/ low therapeutic index
-Many interactions are yet to be identified

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Grapefruit juice effect

Inhibits metabolism of certain drugs; raises the drugs' blood levels

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Timing of drug administration

Some drugs are better tolerated on an empty stomach, others should be taken with food esp. for nausea