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Biochemical Pharmacology > Absorption & Distribution > Flashcards

Absorption & Distribution Flashcards

1
Q

Enteral

A

Refers to anything that hits the stomach/digestive system

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2
Q

Parenteral

A

Anything that doesn’t involve the stomach/digestive system

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3
Q

First pass metabolism

A

The conc. of a drug is greatly reduced before it reaches systemic circulation

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4
Q

Routes of admin. that reduce first pass metabolism

A
  • suppository
  • intravenous
  • intramuscular
  • sublingual
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5
Q

What effects bioavailability?

A
  • First pass metabolism; enzymes, mucosa & liver metabolise drugs
  • Drug formulation; size, salt form, excipients influence absorption
  • Solubility of the drug; very hydrophilic/hydrophobic is poor
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6
Q

How to measure bioavailability

A
  • Compare plasma levels of a drug after oral vs IV
  • Plot plasma conc. v time
  • Measure AUC - total systemic exposure to drug
  • Difference reflects extent of absorption
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7
Q

Bioequivalent

A

When two drugs have;
* comparable bioavailability
* similar time to achieve peak plasma conc.
* same active ingredient

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8
Q

Lipophilicity

A

The more lipophilic a molecule the better the brian penetration

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9
Q

Mechanisms for drug membrane passage

A
  1. Passive diffusion
  2. Carried mediated mechanisms
  3. Paracellular Transport
  4. Ion Trapping
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10
Q

Passive diffusion

A

From high conc. to low conc.
Dominates transmembrane movement of most drugs
Not saturable
Low structual specificty

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10
Q

What does passive diffusion depend on?

A
  • Conc. of drug
  • Oil/water partition coefficient
  • Surface area of absorbing membrane
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11
Q

Carried mediated mechanisms

A
  1. Facilitated diffusion
  2. Active transport
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12
Q

Carried mediated mechanisms

A
  1. Facilitated diffusion
  2. Active transport
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13
Q

Facilitated diffusion

A
  • Requires transmemrane integral proteins
  • No energy required
  • Movement in direction of conc./elctrochemical gradient
  • Carrier protein may be highly selctive
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14
Q

Active transport

A
  • Requires transmembrane integral proteins
  • structurly selective
  • Can be against conc./electrochemical gradient
  • saturable process
  • in or out of cell
  • binds molecule on one side - changes conformation and releases on other
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15
Q

Paracellular Transport

A

Small molecules can go between cells

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16
Q

What limits paracellular transport?

A

Capillaries of CNS and various epithelial tissues with tight junctions

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17
Q

pH and ionisation

A

Many drugs are weak acids or bases - ionized or unionized forms

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18
Q

Distribution

A

Following absorption
drug distributes into interstitial and intracellular fluids

19
Q

1st phase of distribtion

A

well-perfused organs recieve most of drug
* Brain
* liver
* kidney

20
Q

2nd phase of distribution

A

Slower delivery to:
* muscle
* most viscera
* skin
* fat

21
Q

How is tissue distribution determined?

A

By the partioning of the drug between blood and the partiular tissue

22
Q

How is tissue distribution determined?

A

By the partioning of the drug between blood and the partiular tissue

23
Q

Barriers to cross

A
  • Epethelial barriers
  • Capillary barriers
24
Q

Capillary barriers

A
  • Fenestrated capillaries - very leaky (kidneys and glands)
  • Capillaries with desmosomal junctions - slightly leaky (lungs, muscles, heart muscles)
  • Capillaries with tight junctions - not leaky (brain, placenta, testes)
25
Q

Plasma protein binding

A

Slows the rate at which the drug reaches site of action
many drugs are bound to plasma proteins - only free drug can cross capillary membrane

26
Q

Vd

A

apparent volume into which a quantity of drug is distributed to provide the same conc. as it currently is in blood plasma

27
Q

Bone

A

Resrvoir for slow release of toxic agents

28
Q

Chloroquine

A

Taken up by tissues rich in melanin
e.g. retina

29
Q

Tetracyclines

A

Accumulate slowly in bones

30
Q

Amiodarone

A

Accumulates in liver and lung

31
Q

What does tissue binding of drugs usually occur with

A

Cellular constituents;
Proteins, Phospholipids, or nuclear proteins

Generally reversible

32
Q

Why would a drug be bound by tissue?

A

To serve as a reservoir that prolongs drug action

in that same tissue or at a distant site

33
Q

Local toxicity example from tissue binding and accumulation

A

renal toxicity associated with aminoglycoside antibiotics

34
Q

What can bone be a resevoir for?

A

The slow release of toxic agents such as lead or radium

35
Q

What may accumulate in bone by adsorption onto the bone crystal surface

A

Tetracycline antibiotics and heavy metals

36
Q

What may accumulate in bone by adsorption onto the bone crystal surface

A

Tetracycline antibiotics and heavy metals

37
Q

What can result in reduced blood flow?

A

Local destruction of bone medulla

38
Q

What types of drugs are stored in the neutral fat?

A

Lipid-soluble drugs

39
Q

Why is fat a relatively safe reservoir?

A

it has low blood flow

40
Q

What is redistribution?

A

A factor in terminating the effects of a drug

41
Q

Sodium Thiopental

A

Intravenous anesthetic
readily crosses BB
Reaches maximal conc. in brain rapidly
plasma and brain conc. decrease as redistributes
little binding of drug to brain constitutes

42
Q

Placenta

A

Functions as a selective barrier to protect the fetus against the harmful effects of drugs

43
Q

What is placental drug transfer governed by?

A
  • Lipid solubility
  • Extent of plasma binding
  • Degree of ionization of weak acid and bases
44
Q

Fetal plasma pH

A

More acidic than that of mother so ion trapping occurs

45
Q

What limits the entry of drugs and other xenobiotics into the fetal circulation?

A

ABC family of transporters

46
Q

How is the entry of drugs and other xenobiotics into the fetal circulation limited?

A

Vectorial effluc by ABC family transporters

Biochemical Pharmacology (9 decks)

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