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PDA Test 3 > Absorption Lecture > Flashcards

Absorption Lecture Flashcards

1
Q

Define Absorption

A

Process by which unchanged drug proceeds from the site of administration to the site of measurement within the body

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2
Q

Define dose

A

How much drug is given

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3
Q

Define dosage form

A

How the drug is formulated (solid, solution, coated capsule, time-release)

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4
Q

Define Route of Administration

A

Oral, IV, nasal, etc

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5
Q

Define physicochemical properties of the drug

A

Size, lipid solubility, ionization, polarity, stability

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6
Q

Define anatomy and physiology at the site of absorption

A

Transit time, permeability, surface area, transporters, drug metabolism, and blood flow

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7
Q

What does absorption involve?

A

Passage across a biological membrane or tissue barrier

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8
Q

Define diffusion

A

Dependent upon a downward gradient of substance to be passed to the other side

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9
Q

Define facilitated diffusion

A

Made possible by a carrier molecule that the substance interacts with or a channel that in the “open” state allows with no affinity or interaction

  • Channels tend to have a much faster rate of passage vs transporters
  • Dependent on gradients
  • Can be inhibited if competing molecules crowd out the substance of interst
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10
Q

Define active transport

A

Carrier mediated
Energy dependent
Allows molecular movement of substance in opposition to its concentration gradient Shows saturation kinetics and can be inhibited

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11
Q

Define symporter

A

Co-transporter

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12
Q

Define antiportar

A

Anti-transporters

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13
Q

Define Fick’s Law of Diffusion

A

Quantifies the amount of a substance diffusing across a given surface area in a certain amount of time under a specified concenration gradient of the substance (“flux”)

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14
Q

Fick’s Law of Diffusion Equation

A 
J= D (Cout- Cin)/h
J= flux of substance
D= diffusion coefficient
h= thickness of the membrane of the barrier
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15
Q

What affects the passage of drugs across the GI cells into the body?

A
  • Variation in “transit time” and pH of the segments
  • Concentration variations
  • Presence of influx and efflux transport systems
  • Membrane potentials can promote or oppose movement of charged molecules
  • Osmotic effects of water movement
  • Enzymes can modify the drug
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16
Q

We are only ___ % human?

A

10!

The other 90% is bacteria cells

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17
Q

What affects drug absorption in the GI Tract?

A

Anatomy and pH changes

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18
Q

What is the paracellular pathway of absorption?

A

Between adjacent cells

  • Restricted to small, polar molecules
  • Must alter the tight junctions between cells
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19
Q

What is transcytosis/endocytosis of absorption?

A

Absorption into the lymphatic circulation via M cells of Peyer’s patches

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20
Q

What do M cells do?

A

Take up antigens and pathogens in the GI tract in order to potentially alert or cause a response in the immune system

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21
Q

Define surface area?

A

Important in drug uptake

- Orally: small intestine

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22
Q

What increases the surface area of the small intestine?

A

Folds, villi, microvilli

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23
Q

Define bioavailability

A

The fraction of administered drug that reaches the site of measurement in the body (usually done in the peripheral venous blood)

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24
Q

Hepatic first- pass metabolism?

A

Reduce oral drug bioavailability

25
Tablets or capsules administration requires?
Involves both disintegration of the solid form and dissolution into gastric fluid
26
What is the driving force in solutions?
Is the free drug concentration in solution
27
What properties is drug permeability strongly influenced by?
Lipophilicity Charge Size Presence of Facilitated or Active Transport
28
What is lipid solubility related to?
Drug passive permeability across cell membranes
29
Why is lipid solubility important?
Drugs must dissolve in and diffuse across cell membranes composed mostly of a phospholipid bilayer - Key factor for rate of penetration across a barrier
30
How does ionization play into drugs?
Unionized species of a weak acid or base readily crosses membranes - Most organic acids are unionized at a pH < pK - Most organic bases are unionized at a pH > pK
31
How does pH play into drugs?
pH differs in different compartments of the body and can alter drug action
32
How does drug size play into absorption?
Larger molecules have less of an ability to cross membranes or tissue barriers - But they can cross through pores or channels between cells or by receptor-mediated transport systems
33
How does blood flow affect absorption?
This is what carries the drug away once the drug has crossed its limiting barrier membrane - Blood flow influences Cin
34
Blood flow in the small intestine? stomach? lungs?
1 L/min 0.15 L/min 5-7 L/min
35
What if there is a sufficiently high permeability?
Blood flow is rate limiting - Increasing blood flow increases absorption - This are called high-extraction ratio drugs
36
What about low-extraction ratio drugs?
Low permeability | Mostly affected by enzyme induction or inhibition or extent of protein binding
37
What is Oral Enteral Routes of Administration?
Convenient and economical but require cooperation - Not prime for drugs that are poorly soluble, unstable, slowly absorbed or metabolized by the liver or gut enzymes - Efflux transporters may exclude them even if they make it to the GI cells
38
What is Sublingual Enteral Routes of Administration?
Rapid for lipid soluble drugs | Avoids GI tract and first pass metabolism
39
What is Rectal Enteral Routes of Administration?
Used where patient is unconscious or vomiting - Somewhat unpredictable and irregular - First pass metabolism hits 50%
40
What is IV or infusion Parenteral Routes of Administration?
Direct into the blood Very rapid delivery No barriers to absorption Invasive and carries increased chance of adverse reactions
41
What is IM Parenteral Routes of Administration?
Rapid absorption into circulation from aqueous solution, slow from non-aqueous - Delivery of large, polar or unstable compounds that are poorly absorbed from external sites but can cross leaky muscle capillaries - Can be painful, inflammatory or toxic via this route but is easier than IV
42
What is SubQ Parenteral Routes of Administration?
Overcomes permeability limitations to absorption of classic enteral routes
43
What is Intraspinal or intrathecalParenteral Routes of Administration?
"into the subarachnoid space in spinal cord or brain" - Deliver drug to the CNS overcoming the BBB - Often painful, risky, and poor distribution
44
What is Intra-arterial Parenteral Routes of Administration?
"into the arterial blood circulation" | Used for delivery of some imaging agents or for local delivery to a tissue (cancer chemotherapy)
45
What is transdermal administration?
Good for patches and long-term delivery | - Avoid first-pass metabolism
46
What is intraocular administration?
For local delivery to eye
47
What is inhalational or pulmonary administration?
Absorption of gaseous or volatile drugs Local lung delivery - Avoids first-pass in liver
48
What is intranasal delivery?
Delivery to nasal mucous membranes and sinuses
49
Transporter activities include?
Control influx of essential nutrients and the efflux of cellular waste and environmental toxins - Can be drug specific and are used to transport drugs or chemicals through a membrane - Can be facilitated or active
50
ATP Binding Casette Type Subfamily
Primary active transporters - Relay on ATP - Example: P-glycoprotein "efflux" system
51
Solute Carrier Type Subfamily
Facilitated and ion-coupled secondary trasnporters - Drug targets or alter ADME/PK - Examples: SERT and DAT
52
What is the P-glycoprotein system?
Efflux system | Protects the BBB by ejecting anything that enter and shouldn't be in the brain back into the blood
53
What are transporters affect drug pharmacokinetics?
Found in GI tract, renal, and hepatic epithelia - Selectively absorb and help eliminate endogenous substances and xenobiotics such as drugs; work in concert with drug-metabolizing enzymes - Play roles in tissue-specific distribution and may facilitate or impair "drug targeting" efforts in therapy
54
Drug level can lead to what?
``` Absorption into the intestine Therapeutic effects Adverse drug effects Metabolism and excretion via the liver Excretion via the kidneys ```
55
What can transporters at the intestinal mucosa do?
Facilitate or impede drug movement into the circulation | - Intestinal enzymes can also break drugs down before they pass into the circulation
56
How does the liver effect elimination?
- Metabolism to some type of primary metabolite back into the blood if the kidney can handle it OR - Metabolize it in the liver and then put it in the bile so it can be removed via feces
57
What are clearance organs?
Modified the effect of the transporter (decrease uptake or excretion) Raise the concentration in the plasma and the target organ Increasing toxicity
58
What are toxicological target organs?
Increases uptake or decrease efflux than you increase exposure/concentration
59
What is Multidrug Resistance Protein-4
Associated with resistance to antiviral nucleoside analogs that are designed to be utilized as a chain terminator of viral DNA synthesis in diseases such as AIDS and hepatitis

PDA Test 3 (7 decks)

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