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Drug discovery > Lecture 7.1 > Flashcards

Lecture 7.1 Flashcards

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1
Q

What is pharmacokinetics?

A

the study of the time course of drug concentrations in the body. It may be separated into:
Absorption
Distribution
Metabolism
Excretion

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2
Q

What is ADME?

A

Absorption
Distribution
Metabolism
Excretion

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3
Q

What factors could the differences in drug disposition between individuals be accentuated by?

A
  • individual variability
  • diseases, esp of liver and kidney
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4
Q

What is meant by ‘distribution’ in PK?

A

Transfer of drug from one place to another within the body, particularly from plasma to tissue.

–> reversible

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5
Q

What is meant by ‘elimination’ in PK?

A

Removal of drug from the body.

–>irreversible.
–> subdivided into metabolism and excretion

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6
Q

What is meant by ‘metabolism’ in PK?

A

chemical alteration of drugs within the body

site of alteration: liver, also kidneys and skin

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7
Q

What is meant by ‘excretion’ in PK?

A

Removal of drug from the body without chemical alteration.

–> occur from kidney, and also lungs, billary tree, GI tract, sweat,
saliva.

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8
Q

What is meant by first-order elimination/absorption/disposition?

A

A constant fraction of drug present in the body is eliminated / absorbed / distributed per unit time.

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9
Q

What else is ‘first order’ reaction also called?

A

log linear elimination, exponential decay, linear kinetics.

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10
Q

What is meant by zero-order Elimination/ Absorption / Disposition?

A

A constant amount of drug is eliminated / absorbed / distributed per unit time

–> constant rate

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11
Q

What else is ‘zero order’ reaction also called?

A

saturable kinetics

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12
Q

Some drugs have disposition characteristics which are neither completely first order nor zero-order.
What is this type of elimination called?

A

non-linear or Michaelis-Menton Kinetics

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13
Q

For 1st order elimination, what does elimination depend on?

A

concentration

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14
Q

Name some drugs that are eliminated through zero-order elimination.

A

ethanol, lithium, phenytoin, and
salicylates

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15
Q

What are some characteristics of subcutaneous injection of drug?

A
  1. injected hypodermically
  2. absorption of drug dependent on peripheral circulation
  3. severe trauma or poising may impede absorption
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16
Q

What is the danger associated with intravenous injection of drug?

A

temporarily high concentration of the drug will affect a vital organ, e.g. the heart or the brain.

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17
Q

In what organ/fluid/part of the body is intrathecal injection injected?

A

cerebrospinal fluid.

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18
Q

What does the distribution of a drug administered through inhalation depend on?

A

lipid solubility of the drug.

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19
Q

What are some possible routes of drug administration?

A

-oral
-subcutaneous
-intramuscular
-intravenous
-intrathecal
-sublingual
-rectal
-inhalation
-topical

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20
Q

What are some forms of drug?

A

◼ Solid (capsules, tablets and pills)
◼ Volatile liquid
◼ Solution
◼ Aerosol
◼ Gas
◼ Crystalline suspension

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21
Q

The choice of route of administration depends on:

A

◼ Desired onset and duration of
action of the drug
◼ Nature of the drug
◼ Special circumstances
◼ Bioavailability of the drug

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22
Q

What are some characteristics of intravenous administration?

A
  • when oral administration is impractical bc of nature of drug or patient factors
  • rapid onset of action
  • long lasting actions by administering continuously or slow-release form
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23
Q

Give an example of a drug that is administered intravenously

A

penicillin G to treat pneumococcal meningitis

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24
Q

Subcutaneous and intramuscular routes of administration should be avoided for most drugs unless there is a specific indication (i.e., insulin)

True or false

A

True

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25
Rate of attainment of steady-state drug concentration (Css) in plasma; 50% of the steady-state drug concentration is achieved in t1/2 , and 90% is achieved in 3.3 × t1/2. 75% is achieved in 2 x t1/2 True or false
True
26
What happens at the steady-state drug conc in plasma?
drug input (infusion) and output (elimination) are balanced, leading to a plateau in drug plasma concentration.
27
What kind of drugs are destroyed in the stomach and thus not given orally?
Proteinaceous drugs ◼ Insulin for diabetes mellitus ◼ Growth hormone for hypopituitary dwarfism ◼ Oxytocin for dysfunctional labor
28
Some drugs are designed for intravenous injection only and severe necrosis (細胞壞死) has resulted when these agents have been inadvertently deposited in tissues. true or false
true
29
How could the topical application of drugs be enhanced?
1. decreasing barrier function of stratum corneum 2. iontophoresis (by electrical field) or phonophoresis (by ultrasound)
30
What is the pre requisite for the drug to be transported across skin through iontophoresis?
- drug must be ionized - a coupling agent, such as mixtures of mineral oil and glycerin, water and propylene glycol, cream, or an aquasonic gel, is used.
31
What are some coupling agents for iontophoresis?
mixtures of mineral oil and glycerin, water and propylene glycol, cream, or an aquasonic gel
32
What are liposomes?
stable microscopic vesicles formed by phospholipids and similar amphipathic lipids. --> used in Liposomal Drug Delivery System
33
What are liposomes made of?
naturally occurring phospholipids such as egg or soy lecithin --> biodegradable and nontoxic --> similar in structure to those found in living cell membranes.
34
What is the advantage of using liposomes as liposomal drug delivery systems?
can carry soluble, as well as lipophilic, drugs 1. enhance the bioavailability of a drug 2. alter the tissue distribution of an agent 3. prolong the release of a substance in the body
35
Name a drug that are encapsulated in liposomes for delivery
Orciprenaline (异丙喘宁), a bronchodilator
36
What is bioavailability of a drug?
the quantitative term for absorption, and describes the rate and the extent of absorption.
37
How is bioavailability of a drug calculated?
amt of drug in systemic circulation/ amt of drug administered
38
Many factors can influence the bioavailability of orally administered drugs. What are the most important ones?
drug-drug or drug-food interactions, variations in drug formulation and pre systemic metabolism
39
The rate of absorption can often be described by a first-order process. True or false
True
40
What are some drugs that have significant first pass metablism?
propranolol and tricyclic antidepressants
41
When drugs have significant first pass metabolism, it means that the intravenous dose requirement is smaller than the oral dose
True
42
Drug administered IV enters directly into the systemic circulation and has direct access to the rest of the body.
True
43
What are some patient factors that influence the rate and extent of absorption of drugs?
 The surface area available for absorption  Gastric and duodenal pH  The gastric emptying time  Bile salt pool size  Bacterial colonization of the GI tract  The presence and extent of underlying diseases
44
What are some physicochemical factors that influence the rate and extent of absorption of drugs?
 Molecular weight  The degree of ionization under physiologic conditions  Product formulation characteristics  Disintegration and dissolution rates for solid dosages  Drug release characteristics for timed-release preparations
45
why is gastric emptying time a factor that influence the rate and extent of absorption of drugs?
it determines how quickly a drug moves from the stomach to the small intestine, where the majority of drug absorption occurs
46
How do lipid-insoluble substances enter plasma membranes?
penetrate only when they are small enough to pass through the pores. whereas lipid soluble ones travers the membrane by dissolving in lipid phase
47
How is absorption of large lipid-insoluble substances such as sugars and amino acids accomplished?
by specialized transport processes.
48
How does drug particle size relate to its rate of dissolution its absorption?
-rate of dissolution of drug increases significantly as size of drug particle decreases -more soluble drugs are absorbed faster and more completely
49
All solubilized drugs are absorbed. True or false
False. for eg neomycin
50
Is decreasing particle size advantageous for all compounds? why or why not?
No. compounds such as penicillin G and erythromycin tend to decompose in the GI tract
51
What are the advantages of buccal and sublingual absorption?
◼ being noninvasive ◼ producing a rapid onset of action ◼ providing high blood levels ◼ avoiding first-pass effects ◼ circumventing (防止) the exposure of drugs to the acidic and digestive fluid of the stomach ◼ drugs may be easily applied ◼ sufficiently localized ◼ if necessary, readily retrieved
52
Under what mechanism does drug absorption occur from the oral cavity?
passive diffusion of the nonionized form from an aqueous phase to one that is lipid in nature also evidence for carrier-mediated transport
53
Which isomers, levo or dextro, are absorbed from the oral cavity?
levo
54
Under what circumstances is oral administration of drugs impractical?
in conditions causing nausea (作嘔) and vomiting (嘔吐), in patients with convulsions, just before surgery, and in uncooperative patients
55
What route of administration is desirable for inducing anesthesia in children?
rectal
56
In rectal route of drug administration, what are the problem? Can they be overcome?
1. problem of small surface area for absorption --> agents such as surfactants are co-administered with the drugs 2. for drugs undergoing extensive first-pass metabolism, rectal admin. may produce higher plasma level 3. prolonged rectal administration of multiple drugs may produce local irritation or even rectal ulceration.
57
Describe carrier-mediated transport.
substance to be carried forms a complex with a component of the membrane on one side; the complex is then carried through the membrane, the drug or substance is released, and the carrier returns to the original surface and state to repeat the process
58
How does facilitated transport differ from carrier-mediated transport?
facilitated transport: 1. besides a carrier molecule, another transport facilitator is essential 2. does not require energy 3. does not proceed against concentration gradient
59
Give an example of facilitated transport.
vitamin B12 attaches to the intrinsic factor and this complex then attaches to the carrier molecule and is transported.
60
Describe ion pair transport.
organic anions combine with organic cations to form a neutral complex, which is then transported through the membrane by passive diffusion
61
Name the transport mechaisms
1. passive diffusion 2. carrier-mediated transport 3. facilitated transport 4. ion pair transport
62
Does ion pair transport take place against the concentration gradient?
No
63
In addition to the lipid-water partition coefficient, what other factors control the rate of absorption of drugs?
◼ Degree of ionization ◼ Surface area ◼ Gastric emptying time ◼ Blood flow through the region
64
What is pKa of a drug?
the pH value at which one half of the drug exist in its ionic form
65
How to calculate pKa?
pKa = pH + log [HA]/[A-]
66
For a weak acid, what happens at pH < pKa?
The environment is more acidic, so the acid remains mostly non-ionized (HA)
67
For a weak acid, what happens at pH > pKa?
The environment is more basic, so the acid is mostly ionized (A⁻).
68
For a weak base, what happens at pH < pKa?
The environment is more acidic, so the base is mostly ionized (BH⁺).
69
For a weak base, what happens at pH > pKa?
The environment is more basic, so the base remains mostly non-ionized (B).

Drug discovery (23 decks)

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