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Normal Animal > Pharmacokinetics: Routes, Formulation, and Absorption > Flashcards

Pharmacokinetics: Routes, Formulation, and Absorption Flashcards

1
Q

Pharmacokinetics

A
  • what the body does to drug
  • absorption, distribution, metabolism, elimination (ADME)
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2
Q

what factors affect a drug’s ability to pass through membrane?

A
  • molecular weight
  • solubility
  • ionization status
  • concentration gradient
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3
Q

molecular weight physiochemical properties

A
  • smaller drugs cross membranes easier
    • 400-500 Da
    • range where most therapeutic drugs fall
  • exceptions
    • monoclonal antibodies
      • 20-50000 Da
    • drugs bound to protein
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4
Q

plasma protein binding

A
  • drug enters circulation and binds to protein
  • protein bound drugs remain in plasma until no longer protein bound
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5
Q

albumin plasma protein binding

A
  • albumin - weak acids, decreased with inflammation
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6
Q

a1 acid glycoprotein plasma protein binding

A
  • a1 acid glycoprotein - weak bases, increased with inflammation
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7
Q

solubility physicochemical properties

A
  • lipids vs. water
  • lipophilic drugs cross membranes easily and distribute widely
    • intracellular, abscesses, CNS, etc.
  • hydrophilic - confined to plasma and ECF
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8
Q

ionization physicochemical properties

A
  • unionized drugs distribute more widely and become more lipophilic
  • depends on pH and pka
    • “like unionized in like”
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9
Q

pka

A
  • pH at which 50% drug ionized and 50% is unionized
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10
Q

concentration gradient

A
  • higher concentration = more drugs for diffusion
    • can alter with dose and route
  • assume there is enough blood flow to area to deliver drug
    • affected by disease
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11
Q

passive diffusion

A
  • no external energy
  • equilibrium net transfer is zero
  • non selective
  • non saturable - first order (linear)
  • rate diffusion
    • proportional to (Ch-Cl)
    • concentration gradient
  • can pass through aqueous pores if water soluble, lipid soluble will go right through membrane
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12
Q

carrier mediated transport

A
  • drugs lacking sufficient lipid solubility for passive
  • carrier may be specific for drug
  • competition for carrier
  • transport mechanism can be saturated
  • typically for drugs mimic endogenous substances (epi or norepi)
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13
Q

carrier mediated facilitated diffusion

A
  • special transport proteins in membrane
  • goes with gradient
  • does not require energy
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14
Q

active transport

A
  • carrier mediated
  • goes against gradient
  • requires energy
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15
Q

clinical relevance of absoprtion

A
  • drug must be absorbed across membranes into systemic circulation in order to reach its site of action
  • routes play important role
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16
Q

how do you chose a route of administration?

A
  • formulation available of drug
  • therapeutic indiction (seizing cannot give oral drug)
  • pathophysiology of disease
  • target species
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17
Q

what are the main routes of administration?

A
  • IV
  • IM
  • SQ
  • oral
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18
Q

intravenous

A
  • drug injected directly into bloodstream - skipping absorptive phase (100% absorption, cannot be more)
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19
Q

advantages IV

A
  • highest concentrations
  • highest efficacy
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20
Q

disadvantages IV

A
  • highest risk toxicity
  • technically most difficult
  • risk of intracarotid injection goes straight to brain causes seizure, coma, blindness, death
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21
Q

clinical relevance of IV injection

A

IV route preferred for ER for very sick animals whenever possible, ensures drug delivered

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22
Q

intramuscular injection

A
  • muscles highly vascular and absorption from IM route often high
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23
Q

advantages IM

A
  • easy to perform - large animal with large muscle masses (neonates and small animals do not)
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24
Q

disadvantages IM

A
  • possibility of administering drug in a vessel
  • painful
  • drug may cause muscle necrosis, abscess, infection
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25
clinical relevance IM
* often 2nd choice for ER if cannot hit vein, take into account drug formulation
26
subcutaneous injection
* absorption moderate to high, more variable than IM
27
advantages of SQ injection
* easy to perform * less painful than IM
28
disadvantages SQ
* during dehydration and/or shock skin receives less blood flow
29
clinical relevance of SQ
* moderate to severe dehydration or shock can decrease absorption from SQ injection
30
how are water soluble drugs given SQ absorbed
* go from blob between cells (leave blob quickly bc lipophilic) absorbed faster
31
how are lipid soluble SQ drugs absorbed
* can go through cells * takes longer bc do not want to leave lipid blob quickly * more likely to form depot in IM/SQ space * does not mean less will be absorbed
32
sustained release formulation
* drug vehicle affects solubility and absorption
33
fastest to slowest formulation absorption
* slowest: solid dose form * oil based suspensions * oil based solutions * aqueous suspensions * fastest: aqueous solutions
34
intravascular
* IV - directly inject into vein (or artery( * assume 100% absorption
35
extravascular
* every other route * assume less than 100% absorption
36
enternal
* administration via the GI tract * oral (per os; PO; by mouth) * per rectum, oral/buccal transmucosal
37
parental
* everything else * IV/IM/SC
38
oral
* absorption ranges from 0-100% * most variable * slowest * species differences * monogastrics vs ruminants * effects of feeding/diet * fat content
39
clinical relevance of oral
* oral is not preferred route for ER situations
40
advantages oral
* cheap * easy (in most animals)
41
disadvantages oral
* drug loss * administration * vomit/reflux * degradation by stomach acid * rumen/colon microbes * affect on GI flora
42
reasons for poor oral bioavailability
* drug not delivered from its formulation to absorption site in GIT * water soluble to go into solution * lipid soluble to be absorbed across GI membrane * formulations may have solubility enhancers - compounding * drug must go into solution before it can be absorbed, may be rate limiting step for lipid soluble drugs * drug decomposed in GIT - gastric acid or rumen microbes * drug complexed in GIT - chelate with cations * needs carrier mediated transport (too big, too water/lipid soluble, too ionized) * ion trapping * first pass metabolism
43
ion trapping
* stomach is highly acidic, weak acid is unionized in stomach and becomes trapped in gastric surface epithelial cells bc basic (problems with NSAIDs) * higher absorption of basic drugs in SI and higher surface area
44
first pass metabolism
* for some drugs large % of drug absorbed immediately metabolized in gut or liver prior to absorption into systemic circulation
45
how to avoid first pass metabolism
* alter route of administration
46
oral transmucosal
* aka buccal or sublingual * membranes are relatively permeable * rich blood flow * rapid uptake of drug into systemic circulation to avoid first pass metabolism
47
other transmucosal routes
* inhalation, nasal, ocular, vaginal, rectal
48
advantages of per rectum
* access (unconscious or vomiting patients) * taste (none) * can recover drugs before absorption is complete
49
disadvantages of per rectum
* limited surface area, lower fluid content, microbes (degrade drug) * too far cranial drains to portal vein through cranial rectal vein * drug may not stay where you put it
50
transdermal
* drug absorbed through skin into circulation
51
transdermal vs. topical
* topical stays on skin, transdermal goes into circulation not the same
52
Cmax
* maximum plasma concentration * units ug/mL (ng/mL) * typically highest for IV doising * typically lower for PO/IM/SC
53
Tmax
* time to maximum plasma concentration * units hr (min) * for IV dosing occurs within 2-3 minutes or less * highly variable for PO/IM/SC
54
clinical relevance of Cmax and Tmax
* Cmax determines the magnitude of effect and adverse effects * Tmax tells you when the effect/adverse effect will occur; used for drug monitoring
55
area under curve
* influenced by Cmax and Tmax * indicates how much drug is absorbed
56
bioavailability (F%)
* % of administered drug that appears in bloodstream after dosing * two types - absolute and relative * absolute compares EV drug to IV drug
57
relative bioavailability (F%)
* compares EV drug to EV drug * may be routes of administration * may be different formulation
58
bioequivalence
* two drugs have same effect * +/- 20%
59
flip flop phenomenon
* absorption phase is prolonged * sustained release or depot formulations
60
clinical relevance of absorption
* a drug needs to be absorbed to have an effect except topical * low bioavailability means no effect * high bioavailability still better most of the time
61
gastrointestinal disease affect on absorption
* enteral vs. parenteral * d+ * proliferative diseases * v+/refluxing * oral admin is not best route for GI
62
liver disease affect on absorption
* can decrease first pass metabolism and therefore increase oral absorption of some drugs that normally undergo high first pass effects

Normal Animal (22 decks)

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