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BIOM 3090 > Pharmacokinetics-absorption, administration > Flashcards

Pharmacokinetics-absorption, administration Flashcards

1
Q

Absorption, distribution, metabolism, and excretion of a drug
involves transport across cell membranes, which is affected by
several drug characteristics:

A
  • Molecular size & structural features
  • Degree of ionization
  • Relative lipid solubility of ionized/non-
    ionized forms
  • Affinity and binding to serum and
    tissue proteins
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2
Q

Passive diffusion of drug thru cell membranes is generally limited to
_________

A

unbound

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3
Q

True or False: Large lipophilic drugs typically pass thru membranes

A

True

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4
Q

True or False: Passive diffusion thru cell membranes dominates transport for most drugs

A

True

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5
Q

Paracellular passage of molecules happens thru __________ _______

A

Intracellular gaps

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6
Q

What can limit paracellular flow

A

“Tight intercellular junctions

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7
Q

Passive flux across membranes is driven by

A

-Drug concentration gradient across membrane
-Solubility of drug ie. lipid-water partition coefficient
(greater the coefficient, faster the diffusion)
-Surface area of membrane
-Membrane thickness

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8
Q

Flux (molecules/unit time) equation

A

(C1-C2) x Area x Partition Coefficient/ Membrane Thickness

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9
Q

Many drugs are weak acids or weak bases present in solution as
both ________ and ________species

A

un-ionized and ionized

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10
Q

Unionized species (weak acids and bases) are

A

More lipid soluble, more readily diffuse across cell membrane

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11
Q

Ionized species (weak acids and bases) are

A

Less lipid soluble, less able to cross thru cell membranes directly

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12
Q

Transmembrane distribution of a weak electrolyte is influenced by its ________ and the ____ gradient across the cell membrane

A

pKa, PH

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13
Q

pKa

A

pH at which 50% of drug is ionized and 50% is unionized

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14
Q

pKa is usually between

A

pH 3 and pH 11

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15
Q

Henderson-Hasselbach equation

A

log x [Protonated/Unprotonated] = pKa-pH

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16
Q

Drug accumulates on side of cell membrane where ionization is _______

A

highest, (this is called ion trapping)

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17
Q

Basic drugs accumulate in ________ fluids

A

acidic

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18
Q

Acidic drugs accumulate in ________ fluids

A

basic

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19
Q

What determines degree of ionization of drug

A

pH on either side of cell membrane

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20
Q

Will a weakly acidic drug (aspirin) with a pKa of 6.5
accumulate more in intestinal juices (assuming
a pH = 5.4) or in the blood space (assuming a pH
= 7.4) ??

A

Blood space

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21
Q

Will a weakly basic drug (methamphetamine) with a
pKa of 10.0 accumulate more in the urine (assuming
a pH = 6.0) or in the blood space (assuming a pH
= 7.4) ??

A

Urine

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22
Q

2 forms of carrier-mediated transport

A

-Active transport
-Facilitated transporters

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23
Q

Carrier-mediated transport is importantfor molecules: (2)

A

-too large for passive diffusion
-not soluble in lipid for passive diffusion

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24
Q

Carriers are: (3)

A

-Saturable
-Selective
-Inhibitable

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25
Q

Active transporters

A

move molecules against their concentration and
electrochemical gradient, requires energy in form of ATP

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26
Q

Facilitated transporters

A

move large/lipid insoluble molecules down their
electrochemical gradient, no energy input required

27
Q

Example of active transporter

A

Na+-K+-ATPase pumps of
excitable cells such as cardiac myocytes or neurons

28
Q

Example of facilitated transporters

A

eg. glucose via GLUT 4 transporter

29
Q

Pharmacokinetics: what does it mean and list the 4 main points

A

Processes affecting the movement of drugs through
the body ie. what the body does to the drug
* Absorption
* Distribution
* Metabolism
* Excretion

30
Q

Absorption first requires _________of active drug (active pharmaceutical
ingredient) from its dosage form (formulation) before entering circulation for solid
or semi-solid dosage forms

A

dissolution

31
Q

Rate of absorption affects

A

-onset
-duration
-intensity of action

32
Q

Absorption is required for most routes of drug administration except:

A

Intravenous route; intrathecal route, topical route, other minor routes

33
Q

What affects rate of absorption from site of administration

A

-Physiochemical drug factors
-Physiologic factors
-Drug formulation

34
Q

Physiologic factors

A

A large concentration gradient between site of drug administration and
surrounding tissue drives the uptake of drug into the circulation

35
Q

Regional or local _______ ______ has the greatest effect on maintaining a _______ concentration gradient favouring drug absorption

A

Blood flow, large

36
Q

Drug formulation

A

Physical form and chemical ingredients of a medication

37
Q

Drug formulation includes both

A

Includes both the active drug (active pharmaceutical ingredient) and any
inactive chemicals (binders, excipients, preservatives, etc) that comprise a pharmaceutical product ready for administration to the patient by a specified route of administration

38
Q

(Drug formulation) Modifications of the active pharmaceutical ingredient and/or final formulation can be employed to

A

Slow or delay the release of the API for absorption

39
Q

4 points of slowing or delaying release of API for absorption by modifying API

A
  • More convenient as drug is less frequently administered
  • Usually for drugs with short elimination half lives
  • Modifications aimed at prolonging dissolution phase of absorption
  • “Dose-dumping or erratic absorption are potential concerns
40
Q

Bioavailability

A

fraction (%) of administered dose that reaches the
systemic circulation unchanged

41
Q

Bioavailability can be reduced or affected by

A
  • Precipitation of drug at injection site (SC, IM); unavailable for absorption
  • Unable to be absorbed by G.I. tract
  • ‘First pass” elimination effect following oral administration of drugs
42
Q

Unable to be absorbed at G.I tract

A
  • Physicochemical property of drug
  • Reverse transport protein (P-glycoprotein)
43
Q
  • ‘First pass” elimination effect following oral administration of drugs
A
  • Primarily due to liver metabolizing enzymes inactivating drug
  • Enzymes in G.I. tract wall can also metabolize drug
  • Drug can also be excreted in bile
44
Q

Most common method of administration of drugs

A

Enteral: Oral

45
Q

Advantages of enteral (oral) route of administration

A
  • Most convenient for self-administration
  • Most economical route
  • Usually safer than injection
  • Minimal risk of infection
  • Can induce vomiting to potentially remove drug
46
Q

Disadvantages of enteral (oral) route

A
  • Absorption may be erratic
  • Enteric coating protects some drugs against gastric juices/acids
  • Patient compliance problems
  • Not for unconscious patients
  • Emesis and G.I. irritation possible
  • “first pass elimination” effect possible
47
Q

Enteral:other minor routes

A

-Oral transmucosal (sublingual and buccal)
-rectal

48
Q

Routes of administration

A

-Enteral: oral
-Enteral:other minor routes
-Parenteral
-Parenteral:other routes

49
Q

Enteral: other minor routes

A

-Oral transmucosal (sublingual and buccal)
-Rectal

50
Q

Parenteral

A

-Subcutaneous injection
-Intramuscular injection
-Intravenous injection

51
Q

Parenteral: other routes

A

-Topical
-Transdermal

52
Q

Subcutaneous injection

A

Injection is administered in the tissues lying below the skin

53
Q

Advantages of subcutaneous injection

A
  • Suitable for solid pellets eg. Contraceptives
  • Suitable for insoluble suspensions
  • Easier to administer than IV
54
Q

Disadvantages of subcutaneous injection

A
  • Absorption slower than IM route
  • Can be erratic depending blood flow to site
  • Not suitable for large volumes
  • Pain and/or necrosis with irritating injectable drug solutions
  • Technical skills needed for some injections
  • Generally, drug is irretrievable once injected
55
Q

Intramuscular injection

A
  • Injection is administered into the muscle
  • gluteus maximus,
  • vastus lateralis of the thigh
  • deltoid of upper arm
  • other minor sites
56
Q

Advantages of intramuscular injection

A
  • Absorption is typically rapid for drugs in aqueous solution; oily
    suspensions will form depot
  • Safe, easier than IV
57
Q

Disadvantages of intramuscular injection

A
  • Local pain and swelling with irritating solutions
58
Q

Topical (parenteral:other routes)

A

Drugs are applied topically to the eye, skin and the mucus membranes
(conjunctiva, nasopharynx, vagina, urethra, urinary
bladder)

59
Q

Advantages of topical route

A

drug delivered locally; can achieve very high conc’n

60
Q

Disadvantages of topical route

A
  • may be absorbed systemically
  • may not remain at desired site
61
Q

Transdermal route (parenteral:other route)

A

Drugs applied to skin absorbed into the systemic circulation

62
Q

Advantages of transdermal route

A
  • absorption enhanced by abraded, denuded or burned skin
  • controlled release eg. nicotine and fentanyl patches
  • prolonged duration of action
  • by passes “first pass elimination” effects
63
Q

Disadvantages of transdermal route

A

therapeutic blood levels are slow to achieve; delay onset of action

BIOM 3090 (12 decks)

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