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BIOM 3090 > Pharmacokinetics-absorption, administration > Flashcards

Pharmacokinetics-absorption, administration Flashcards

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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
Active transporters
move molecules against their concentration and electrochemical gradient, requires energy in form of ATP
26
Facilitated transporters
move large/lipid insoluble molecules down their electrochemical gradient, no energy input required
27
Example of active transporter
Na+-K+-ATPase pumps of excitable cells such as cardiac myocytes or neurons
28
Example of facilitated transporters
eg. glucose via GLUT 4 transporter
29
Pharmacokinetics: what does it mean and list the 4 main points
Processes affecting the movement of drugs through the body ie. what the body does to the drug * Absorption * Distribution * Metabolism * Excretion
30
Absorption first requires _________of active drug (active pharmaceutical ingredient) from its dosage form (formulation) before entering circulation for solid or semi-solid dosage forms
dissolution
31
Rate of absorption affects
-onset -duration -intensity of action
32
Absorption is required for most routes of drug administration except:
Intravenous route; intrathecal route, topical route, other minor routes
33
What affects rate of absorption from site of administration
-Physiochemical drug factors -Physiologic factors -Drug formulation
34
Physiologic factors
A large concentration gradient between site of drug administration and surrounding tissue drives the uptake of drug into the circulation
35
Regional or local _______ ______ has the greatest effect on maintaining a _______ concentration gradient favouring drug absorption
Blood flow, large
36
Drug formulation
Physical form and chemical ingredients of a medication
37
Drug formulation includes both
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
(Drug formulation) Modifications of the active pharmaceutical ingredient and/or final formulation can be employed to
Slow or delay the release of the API for absorption
39
4 points of slowing or delaying release of API for absorption by modifying API
* 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
Bioavailability
fraction (%) of administered dose that reaches the systemic circulation unchanged
41
Bioavailability can be reduced or affected by
* 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
Unable to be absorbed at G.I tract
* Physicochemical property of drug * Reverse transport protein (P-glycoprotein)
43
* ‘First pass” elimination effect following oral administration of drugs
* 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
Most common method of administration of drugs
Enteral: Oral
45
Advantages of enteral (oral) route of administration
* Most convenient for self-administration * Most economical route * Usually safer than injection * Minimal risk of infection * Can induce vomiting to potentially remove drug
46
Disadvantages of enteral (oral) route
* 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
Enteral:other minor routes
-Oral transmucosal (sublingual and buccal) -rectal
48
Routes of administration
-Enteral: oral -Enteral:other minor routes -Parenteral -Parenteral:other routes
49
Enteral: other minor routes
-Oral transmucosal (sublingual and buccal) -Rectal
50
Parenteral
-Subcutaneous injection -Intramuscular injection -Intravenous injection
51
Parenteral: other routes
-Topical -Transdermal
52
Subcutaneous injection
Injection is administered in the tissues lying below the skin
53
Advantages of subcutaneous injection
* Suitable for solid pellets eg. Contraceptives * Suitable for insoluble suspensions * Easier to administer than IV
54
Disadvantages of subcutaneous injection
* 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
Intramuscular injection
* Injection is administered into the muscle * gluteus maximus, * vastus lateralis of the thigh * deltoid of upper arm * other minor sites
56
Advantages of intramuscular injection
* Absorption is typically rapid for drugs in aqueous solution; oily suspensions will form depot * Safe, easier than IV
57
Disadvantages of intramuscular injection
* Local pain and swelling with irritating solutions
58
Topical (parenteral:other routes)
Drugs are applied topically to the eye, skin and the mucus membranes (conjunctiva, nasopharynx, vagina, urethra, urinary bladder)
59
Advantages of topical route
drug delivered locally; can achieve very high conc’n
60
Disadvantages of topical route
* may be absorbed systemically * may not remain at desired site
61
Transdermal route (parenteral:other route)
Drugs applied to skin absorbed into the systemic circulation
62
Advantages of transdermal route
* 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
Disadvantages of transdermal route
therapeutic blood levels are slow to achieve; delay onset of action

BIOM 3090 (12 decks)

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