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2060B: Pharmacology > Module 2: Absorption > Flashcards

Module 2: Absorption Flashcards

1
Q

Define pharmacokinetics:

A
  • Is defined the study of drug movement in the body.

- Is what the body does to the drug

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2
Q

• Pharmacokinetics is composed of four basic processes (ADME):

A

o Absorption
o Distribution
o Metabolism
o Excretion

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3
Q

Describe absorption:

A

Drug absorption is the movement of the drug from the site of administration into the blood

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4
Q

The rate of absorption determines…

A

… how quickly the drug effect will occur

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5
Q

The amount of drug absorption determines…

A

… how intense the effect of the drug will be.

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6
Q

What are the (6) factors that affect absorption?

A
  1. Rate of Dissolution
  2. Surface Area
  3. Blood Flow
  4. Lipid Solubility
  5. pH Partitioning
  6. Activity of Drug Transport Proteins
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7
Q

Rate of Dissolution:

  • Define rate of dissolution
  • Drugs must dissolve before they can be…
  • Drugs with a fast rate of dissolution will have…
A
  • Dissolution means dissolving
  • … absorbed
  • … a faster onset of action than drugs with slow dissolution.
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8
Q

Surface Area:

  • What is true about surface area?
  • The larger the surface area, the…
  • What has a greater surface area? Stomach or small intestine?
A
  • Surface area is a major determinant of drug absorption.
  • … the faster drug absorption is.
  • Small intestine due to villi
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9
Q

Blood Flow:

  • Drug absorption is fastest in areas with…
  • Areas with a high blood flow maintain…
  • Areas with low blood flow do not maintain
  • Does exercise increase absorption?
  • When is blood flow decreased?
A
  • … High blood flow
  • … a concentration gradient which drives absorption
  • … as great of a concentration gradient
  • Yes
  • Blood flow is decreased in heart failure, severe hypotension, hypothermia and circulatory shock.
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10
Q

Lipid Solubility:

  • Drugs with high lipid solubility (i.e. lipophilic drugs) are absorbed …
  • Lipophilic drugs are able/not able to cross the cell membrane
  • Hydrophilic drugs are able/not able to cross the cell membrane
A
  • … more rapidly than water soluble (i.e. hydrophilic) drugs.
  • are able
  • are not able
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11
Q

pH Partitioning:

- Drug absorption is greater when there is …

A

… a difference between the pH at the site of administration and the blood such that the drug is ionized in the blood.

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12
Q

Activity of Drug Transport Proteins:

  • The rate and extent of drug absorption can be significantly impacted by …
  • Uptake drug transporters increase/decrease the absorption of drugs (outside into the cell)?
  • Efflux drug transporters increase/decrease the absorption of drugs (inside cell to outside)?
A
  • … Drug transporters
  • Increase
  • Decrease
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13
Q

What are the 8 major routes of drug administration?

A
  1. Oral (PO = per os which is latin for by mouth)
  2. Sublingual
  3. Transdermal
  4. Rectal
  5. Intravenous (IV)
  6. Subcutaneous (SubQ or SC)
  7. Intramuscular (IM)
  8. Pulmonary
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14
Q

What are enteral vs. parenteral routes of administration?

  • Provide examples
  • What are 3 other routes?
A

Enteral – Routes of administration that involve the gastrointestinal tract.

  • Oral
  • Rectal

Parenteral – Routes of administration that do not involve the gastrointestinal tract.

  • IV
  • Subcutaneous
  • Intramuscular

Other

  • Sublingual
  • Transdermal
  • Pulmonary
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15
Q

What is the most common method of drug administration?

A

Oral

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16
Q

Is drug absorption greater in the stomach or small intestine? Why?

A

Small intestine

- Larger surface area

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17
Q

Are weak acids better absorbed in the acidic environment of the stomach?
- Why or why not?

A

Based on the pH effects weakly acidic drugs should be better absorbed in the acidic environment of the stomach because they would un-ionized.

  • However, the surface area of the stomach is small, and the stomach is covered with a thick layer of mucous.
  • Therefore, the rate of drug absorption in the intestine will be greater than the stomach, even if the drug is ionized!
  • The bottom line is for most drugs, oral absorption is greatest in the intestine.
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18
Q

What are advantages and disadvantages of oral administration?

A

Advantages:

  • Safety
  • Convenience
  • Economical

Disadvantages:

  • Incomplete absorption
  • Variable absorption
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19
Q

Describe the pharmaceutical phase vs. the dissolution phase when swallowing a tablet:

A

Pharmaceutical Phase:

  • Swallow tablet
  • Tablet disintegrates into granules and then smaller particles

Dissolution Phase:

  • Drug dissolutes
  • Particles are dissolved in gastric fluid
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20
Q

What happens if the drug does not completely disintegrate or does not go into solution?

A

Absorption is reduced

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21
Q

What is gastric emptying?

A

Gastric emptying is quite simply the movement of the stomach contents into the intestine

22
Q

True or false:

Since the rate of drug absorption is greater in the intestine, things that increase gastric emptying also increase the rate of drug absorption.

A

True

23
Q

What are factors that increase gastric emptying?

A
  • Taking meds on an empty stomach
  • Taking meds with cold water
  • Lying on right side
  • High osmolality feeding (tube feeding)
  • Taking prominent drug (drug that increase GI motility)
24
Q

What are factors that reduce gastric emptying?

A
  • High fat meals
  • Heavy exercise
  • Lying on left side
  • Taking drugs that inhibit vagus nerve
25
Q

What is a drug that has enteric coating?

- Provide an example

A

Drugs with enteric coating are covered with a special coating that prevents their dissolution in the acidic environment of the stomach.
- Ex. Drugs that cause damage to the stomach

26
Q

What do enteric coatings dissolve?

A

Once the drug passes into the more alkaline duodenum

27
Q

Define bioavailability:

A

Bioavailability is the fraction of a dose of drug that reaches the systemic circulation unchanged.

28
Q

What is bioavailability influenced by?

A
  1. Drug formulation
  2. Route of Administration
  3. Degree of Metabolism
29
Q

What is sublingual administration?

  • Where is it absorbed?
  • Where is it drained?
  • What does it avoid?
  • What type of drug must is be and what charge will it hold?
A

Involves placing a drug under the tongue.

  • The drug dissolves and is absorbed across the oral mucosa
  • Venous drainage from the oral mucosa is to the superior vena cava, the superior vena cava takes blood to the heart
  • Drugs administered sublingually avoid first pass metabolism through the liver
  • Lipophilic and uncharged.
30
Q

What are transdermal drug administrations?

A

Typically patches, ointments, sprays or lotions which provide constant plasma drug levels with minimal peaks and troughs

31
Q

What must transdermal drugs be able to do?

A

The epidermis provides a lipid barrier… therefore, drugs must be lipophilic enough to penetrate the skin
- Drugs must also be relatively hydrophilic in order to dissolve in the extracellular fluid

32
Q

Ideal transdermal preparations have some degree of…

A

… lipophilicity and some degree of hydrophilicity and are usually small (< 600 Da) molecules

33
Q

How is tolerance avoided with transdermal drugs?

- Provide an example.

A

Tolerance may develop unless drug-free periods are enforced

- Typically, patches are removed for 6 – 10 hours per day to avoid tolerance.

34
Q 
What are (5) factors that affect transdermal absorption?
- Explain each
A
  1. Thickness of the skin – Transdermal absorption is inversely proportional to skin thickness.
  2. Hydration – Transdermal absorption is increased when the skin is well hydrated.
  3. Hair follicles – Provide routes for drugs to bypass the barrier function of the epidermis.
    - In general, the greater the number of hair follicles, the greater the transdermal absorption is.
  4. Application Area – The greater the application area, the greater the transdermal absorption.
  5. Integrity of the barrier – In conditions such as psoriasis, burned or abraded skin, transdermal absorption is increased.
35
Q

When is rectal drug administration useful?

A

Useful when the patient is unconscious or vomiting.

36
Q

What do rectally administered drugs bypass?

A

Approximately 50% of rectally administered drugs bypass the liver (an important site for drug metabolism).

37
Q

How are drugs administered rectally?

A

Administration: The drug is inserted into the rectum as a suppository
- The suppository dissolves and the drug cross the rectal mucosa into the blood.

38
Q

What are disadvantages of rectal administration of drugs?

A

Disadvantages include incomplete absorption and some drugs may irritate the rectal mucosa.

39
Q

How are IV drugs injected?

- What is the most commonly used vein?

A

Drug is injected directly into a peripheral vein
- Most commonly used veins are those on the back of the hand or the median cubital vein at the elbow although any visible vein may be used.

40
Q

What are two methods of IV drugs?

A

1) In IV bolus a single dose is administered over a short time period.

2) In an IV drip a drug is administered under continuous infusion over a prolonged period
- Drugs are typically diluted in a “vehicle” such as saline in an IV bag

41
Q

Advantages and disadvantages of IV drugs?

A

Advantages:

  • No barriers to absorption, bioavailability is 100%.
  • Allows precise control of drug dosage & duration of action.
  • Allows administration of poorly soluble drugs that must be diluted in a large volume.
  • Allows injection of drugs that are irritants (i.e. chemotherapeutic drugs) they can be injected slowly, diluted in blood

Disadvantages:

  • Expensive, invasive and inconvenient.
  • Drug cannot be removed once injected.
  • Risk of infection and fluid overload.
  • Risk of injecting wrong formulation (IM formulation sometimes injected IV by accident).
42
Q

How are subcutaneous drugs administered?

A

Drug is injected beneath the skin into the subcutaneous tissue.

43
Q

What is a barrier to absorption with subcutaneous drugs?

A

The only barrier to absorption is the capillary wall.

44
Q

What types of drugs cannot be injected subcutaneously? Why?

A

• Irritant drugs must not be injected subcutaneously as this will cause severe pain and/or tissue sloughing.

45
Q

What is the primary rate of absorption with subcutaneous drugs?

A

1) Blood flow

2) Water solubility

46
Q

How are intramuscular drugs administered?

A

Drug is injected directly into muscle tissue.

47
Q

What is absorption determined by in IM drug administration?

- Primary determinant of rate of absorption?

A

Absorption is determined by the ability of the drug to pass through fenestrations in the capillary wall
- Blood flow

48
Q

Advantages/disadvantages of IM drug administration?

A

Advantages:

  • Can be used for poorly soluble drugs
  • Can use it to administer depot preparations (preparations in which the drug is absorbed slowly over time).

Disadvantages:

  • Pain/discomfort
  • May cause local tissue and/or nerve damage if the injection is done improperly
49
Q

What affects IM absorption?

  • Where is blood flow the greatest?
  • What can increase absorption?
  • What can decrease absorption?
A

Blood flow is different depending on which muscle is used for injection

  • In general blood flow is deltoid > vastus lateralis> gluteal
  • Exercise increases blood flow and may therefore increase absorption for IM drugs.
  • Blood flow may be decreased in heart failure, severe hypotension and hypothermia
50
Q

How are pulmonary drugs administered?

  • What are 2 advantages?
  • What types of drugs are used?
A

Gaseous and volatile drugs can be inhaled and absorbed into the blood through the pulmonary epithelium.

1) Absorption is very rapid (almost instantaneous) due to the large surface area of the lung.
2) In the case of pulmonary disease (i.e. asthma), the drug is delivered to its site of action which is a major advantage.

Drugs such as general anaesthetics used in surgery are also often administered by the pulmonary route of administration.

2060B: Pharmacology (18 decks)

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