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Y1 - Pharm > 1 - Absorp --> Excrete > Flashcards

1 - Absorp --> Excrete Flashcards

1
Q

integrated pharmacology: define

A

combining study methodology w/ drug development;

this is the first step in rational approach to drug therapy; incl:

  • appropriate prescribed dose
  • dose administered
  • routes of admin
  • conc. @ site of admin
  • pharmacological effects
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2
Q

what factors determine amount of drug present at its active site at any given time?

A

“ME RAD”

  • Metabolism (biotransformation)
  • Excretion
  • Route of drug admin
  • Absorption
  • Distribution
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3
Q

Which 3 factors depend on patient status

(that also determine the amount of drug present at its active site at any one time)?

A

MAE

  • Metabolism
  • Absorption
  • Excretion
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4
Q

Which factors/parameters fall under “pharmacokinetics”?

A
  • “ADME”
    • Absorption
    • Distribution
    • Metabolism
    • Excretion
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5
Q

pharmacoKINETICS: define

A
  • the FATE of substances administered to living organism/
  • how the body handles the drug
  • FACTORS: “ADME”
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6
Q

pharmacoDYNAMICS: define

A
  • interactions between drug and biological system
  • pharmacological response (“what does the drug do re: outcomes?”)
  • Outcomes:
    • Clinical response = Toxicity or Efficacy
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7
Q

the outcomes/pharmacological effect of a drug would be referred to as what?

A

the pharmacoDYNAMICS of a drug

(i.e. clinical response = toxicity or efficacy)

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8
Q

what are the 2 overarching categories: routes of drug administration?

A
  • ENTERAL = ORAL
  • PARENTERAL = “NOT ORAL”
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9
Q

ENTERAL drug admin:

defiine, examples and key characteristics

A
  • ORAL ADMIN
  • Ex: Oral, Sublingual, Rectal
  • KC:
    • *MOST COMMON & relatively SAFE
    • May cause GI irritation
    • NOT GOOD FOR EMERGENCY
    • Undergoes first pass metabolism
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10
Q

what is the most common type of drug admin? why?

A

oral admin (aka enteral)

it is common, relatively safe, and good for patient compliance

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11
Q

what is the benefit of sublingual versus traditional oral admin?

A

SUBLINGUAL (under the tongue) eliminated first pass biotransformation

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12
Q

first pass metabolism: define

A

aka first pass effect; or presystemic metabolism

phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced BEFORE it reaches systemic circulation

(therefore can limit the oral bioavailability of a drug –> limiting effectiveness of oral route)

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13
Q

examples of parenteral admin.

A
  • respiratory (inhalation)
  • injectible (IV, SC, IM)
  • skin (topical, transdermal, inunction - rubbing an ointment or oil into the skin)
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14
Q

benefits of the following drug admin routes:

  • rectal
  • resp
  • subQ
  • IM
  • IV
  • Skin
A
  • rectal –> 50% bypasses the liver
  • resp –> inhalation for local or systemic effect
  • subQ –> under the skin
  • IM –> used for DEPOT effect
  • IV –> directly into bloodstream, rapid onset, excellent in emergency, can be dangerous
  • Skin –> topical or transdermal
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15
Q

which routes BYPASS the liver?

A

transdermal

subQ

IM

IV

INHALATION

RECTAL

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16
Q

key dosage forms?

A
  • tablets - tablets, capsules, caplets
  • liquid - aqueous, useful for pediatric formulations
  • gaseous (e.g. nitrous oxide)
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17
Q

what is imperative to get from a patient before prescribing a drug?

A

A THOROUGH CASE HISTORY! you need to know every drug (prescribed or OTC or supplements) the patient is taking –>

important for many drug reactions

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18
Q

what does an idealized plasma concentration vs. time curve look like?

how does reality differ?

A

Looks like a gradual curve;

but SOME DRUGS CAUSE A SPIKE

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19
Q

4 types of drug absorption?

define each

A
  • passive diffusion: *best possible result –> drug moves across membranes based on its lipid/water partition coefficient
  • active transport: involves carrier proteins, saturable and utilize energy
  • facilitated diffusion: carrier-mediates, w/ conc. gradient
  • filtration: passive thru membrane pores
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20
Q

why is drug absorption important?

A

once a drug is administered, it MUST be absorbed thru biological membranes to produce a systemic effect

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21
Q

which type of drug absorption is saturable?

which is not saturable?

(passive vs. active)

A

ACTIVE is saturable; as it uses energy and runs out of ATP, can’t continue

PASSIVE IS NOT SATURABLE and the rate-absorption will increase as the concentration increases

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22
Q

Factors affecting PASSIVE DIFFUSION?

How do these affect diffusion?

A
  • CONCENTRATION
    • INC. con –> FASTER absorption rate
  • LIPID-SOLUBILITY
    • INC lipid solubility –> FASTER absorption rate
  • MOLECULAR WEIGHT
    • DEC molecular weight –> FASTER absorption rate
  • SURFACE AREA
    • INC molecular weight –> FASTER absorption rate
  • REGIONAL BLOOD FLOW
    • INC regional BF –> FASTER absorption rate
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23
Q

how does increasing lipid solubility of a drug affect the absorption?

why?

A

THE MORE LIPID SOLUBLE –>the greater the rate of absorption

BECAUSE membranes are lipophilic/ hydrophobic

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24
Q

biochemistry of drugs?

(acid/base, ionization)

A
  • many drugs are either WEAK ACIDS or WEAK BASES
  • can exist in both IONIZED (charged) or NON-IONIZED (uncharged) forms
  • non-ionized form is MORE LIPID SOLUBLE, and therefore crosses the membrane better
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25
Q

what factors determine the degree of ionization of a drug?

A

based on pH of the physiological compartment &

pKa of the drug

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26
Q

Henderson Hasselbach: WEAK ACID

A

a neutral molecule that can dissociate into an anion and hydrogen atom –>

*note: protonated form of weak acid is neutral, lipid-soluble form

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27
Q

henderson hasselbach: WEAK BASE

A

a neutral molecule that can form a cation (positively charged molecule) by combining w/ a proton

28
Q

why will more aspirin absorb into the stomach rather than the small intestine?

A

since stomach is more acidic –> aspirin (weak base) is predominantly in HA (protonated) form and can pass through

29
Q

factors affecting distribution?

A
  • physicochemical properties
  • cardiac output
  • regional blood flow
  • degree of plasma protein binding
  • degree of tissue protein binding
  • CNS and placenta (if it crosses or not)
30
Q

when does displacement of class I drug occur?

A

when administered simultaneously with a class II drug

(class II displaces class I when administered together)

31
Q

what effect does class I on have a class II drug?

A

class I drug will iNCREASE THE BIOAVAILABILITY OF A CLASS II drug

32
Q

bioavailability: define

A
  • subcategory of absorption
  • the fraction of an administered dose of unchanged drug that reaches the systemic circulation (amount of drug administered that enters bloodstream unchanged)
33
Q

general rules for oral absorption?

(acids/bases,

ionized molecules)

A
  • acid/base
    • weak ACIDS –> initial absorption in stomach; major portion in upper pt of sm intestine
    • weak BASE –> absorbed in upper pt of small intestine
  • ionization
    • CHARGED molecules –> poorly absorbed
    • NEUTRAL MOLECULES ARE READILY ABSORBED
34
Q

what factors affect bioavailability?

A
  • first pass metabolism
  • solubility of drug
  • chemical stability in the GI tract
35
Q

redistribution: define

A

as drugs are NOT STATIC in the body, this is where the drug goes;

conc of drug will diminish over time

(drug is often stored in fat)

36
Q

bioequivalence means two drugs have the same…

A
  • same PEAK HEIGHT CONCENTRATION
  • same TIME to peak height
  • same AREA under blood conc curve
37
Q

what factors determine INITIAL DISTRIBUTION PATTERN and EXTENT?

A
  • physicochemical properties of drug
    • ability of drug to pass thru membrane
  • lipid solubility/pKa/molecular weight
  • membrane carrier systems (present or absent?)
  • **cardiac output
    • regional BF to various tissues and size of organs
    • may accumulate less rapidly in skeletal musc. & slower in adipose tissue
  • degree of plasma-protein binding –>
    • facilitates absorption, but may reduce ability of drug to enter other tissues
    • drugs may displace each other from binding sites –> adverse rxns
  • degree of binding to tissue proteins
38
Q

what other special considerations affect dist. pattern and extent?

A
  • CNS –> drug may not cross BBB
  • placenta-fetus
  • milk-nursing infants
39
Q

typical physiological volumes:

  • plasma
  • interstitial fluid
  • intracellular fluid
  • total body weight
A
  • plasma: 4L
  • interstitial fluid: 10L
  • intracellular fluid: 28L
  • total body weight: 42L
40
Q

what are the possible termination pathways of drug action?

A
  • redistribution
  • elimination
    • metabolism or (biotransformation)
    • excretion
41
Q

redistribution: define

A
  • mvmt of drug AWAY FROM ACTIVE SITE –> other tissues to be stored
  • factors affecting this:
    • physicochem prop (e.g. more lipid soluble –> more redistribution)
    • BF
42
Q

metabolism: define

and OUTCOMES

A
  • interaction of drug w/ biological system –> causing chemical change in drug (resulting in metabolite/metabolic product)
  • outcomes?
    • inactive
    • active
    • more toxic
43
Q

what is the purpose of drug metabolism?

A

the process makes drug LESS LIPID SOLUBLE/ MORE WATER SOLUBLE –> more READILY EXCRETED in aqueous excretions (urine)

(because MOST drugs are LIPID SOLUBLE, non-ionized @ physiological pH, and are partially bound to plasma proteins

44
Q

what are the categories of metabolic reactions?

A

phase I (non-synthetic)

phase II (synthetic)

45
Q

what is a phase I reaction?

A

(non-synthetic)

to convert parent drug –> more polar metabolite

if sufficiently polar/hydrophilic –> metabolites are excreted

(E.g. oxidation, reduction, hydrolysis(

46
Q

what is a phase II reaction?

A

synthetic rxn

  1. adds group to substrate (conjugation)
  2. forms high-energy intermediates & transferases
  3. catalyzes coupling of endogenous substrate w/ drug/metabolite
  4. *MOST yield inactive products
47
Q
  1. which type of metabolic rxn prepares drug for excretion?
  2. which type inactivates the drug?
A
  1. phase I
  2. phase II
48
Q

where does metabolism occur?

A
  • most ABSORPTION (after oral admin) from small intestine –> transported via portal system to liver
  • most METABOLISM occurs in LIVER (first pass effect - where it may be partially metabolized)
49
Q

what is the microsomal mixed function oxidase system?

A

microsomes: vesicles that from from lipophilic SER membranes being homogenized/fractionated;

mixed function oxidases: metabolic enzymes that remain assoc. w/ this fraction

enzymes require reducing agent (NADPH) and molecular oxygen –>

  • NADPH-cytochrome p450 reductase
  • *cytochrome p450 acts as terminal oxidase
50
Q

cytochrome p450:

define and characteristics

A
  • catalyze variety of chem ring and side chain hydroxylation –> changing molecules (mult. cytochrome forms exist w/ differing substrate specificity
  • requires IRON (bc it’s a transition metal)
  • ***Complexity of Cytochrome P450 system predominant and affects what we do; how we treat
    • MUST know cytochrome metabolism
    • everytime it goes thru the cycle, 1 CO is produced
51
Q

examples of non-cytochome p450 mediated phase I rxns?

(oxidation can still occur by other means)

A
  • *XANTHINE oxidase –> which produces uric acid
    • allopurinol, tx of chronic gout
  • alcohol dehydrogenase: alcohol metabolism
52
Q

factors influencing drug metabolism?

A
  • BF and entry (rate) into liver
  • enzyme inhibition and induction
  • drug-drug interactions
  • individual patient differences
  • genetic factors (polymorphisms)
  • diet and environment
  • age and gender
53
Q

enzyme induction: define

A
  • some drugs (w/ repeat admin) can inc. rate of synthesis/reduce rate of degradation of p450 enzymes –> thereby“inducing” cytochrome p450 activity
  • inc cytochrome p450 activity –> inc metabolism of some drugs
54
Q

enzyme INHIBITION: define

A
  • some drugs can COMPETE w/ another drug for same metabolic enzyme –> forming complex w/ and inactivating enzyme –> INHIBIT cytochrome p450 activity
  • e.g. acute ethanol, cimetidine, disulfiram
55
Q

which inducers affect the corresponding drug metabolism?

  • phenobarbital
  • rifampin
  • chronic ethanol
  • St. john’s wort
A
56
Q

which INHIBITORS affect/reduce the corresponding drug metabolism?

  • ethanol (Acute)
  • cimetidine
  • disulfiram
A
57
Q

excretion: define

A

removal of drug/metabolites from the body –> external environment

*important in preventing/min. toxic effects of drugs

58
Q

routes of excretion for drugs?

A
  • volatile drugs: e.g. inhalational general anesthetics –> eliminated thru lungs/exhaled air
  • non-volatile drugs: e.g. water-soluble –> elim. by bodily excretions
    • urine –> kidney/renal fxn
    • bile –> gallbladder
59
Q

how is drug excreted IF NOTHING ELSE HAPPENS TO IT AS IT PASSES THRU THE NEPHRON?

A

THEN the drug (water soluble, ionized) is excreted into the urine.

60
Q

active tubular secretion: define

A
  • a carrier mediated active transport process in the proximal tubule
  • organic acids and bases may enter the nephron (separate systems for acids and bases).
  • Drugs can compete with each other or endogenous compounds fortransport
61
Q

active tubular reabsorption: define

A

an active transport process in the proximal tubule –> drugs may be reabsorbed back into the general circulation

62
Q

passive reabsorption: define

A
  • Process in the proximal and distal tubules in which a drug can re-enter the circulation by passive diffusion.
  • Relatively lipid-soluble, non-ionized drugs will be reabsorbed instead of being excreted.
  • By pharmacologically changing the pH of the tubular filtrate, it is possible to alter the excretion of a drug (this is referred to as ion-trapping).
63
Q

biliary excretion: define

A

Drugs from the general circulation may enter the liver and be excreted into the bile. There are at least three different carrier-dependent systems, and competition can occur w/in each group:

  • for organic acids,
  • for organic bases, and
  • for some steroids.

Drugs or their metabolites which have entered the gut via the bile may then be:

  • directly excreted in the feces; OR
  • undergoes enterohepatic recirculation
64
Q

enterohepatic recirculation: define

A

drug or metabolite can re-enter the blood stream and prolong its half-life in the body.

65
Q

zero order (elimination) kinetics: define

A

rate of elimination does not increase or decrease with changes in plasma concentration.

(e.g. ethanol)

66
Q

FIRST ORDER kinetics: define

A

rate of removal is therefore proportional to their plasma concentration;

  • a plasma half-life can be determined
  • & conc of most drugs in the body is considerably less than that required to saturate the body’s eliminating capacity
67
Q

factors altering rate of elimination?

A
  • age
  • environment
  • disease
  • gender
  • drug-drug interactions
  • individual variation

Y1 - Pharm (12 decks)

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