3. Drug Absorption

Front 1

What is drug absorption?

Back 1

The movement of a drug from its site of administration into the central bloodstream.

Front 2

What is required for absorption of solid dose forms of drugs?

Back 2

Dissolution of the tablet or capsule

Front 3

What are doctors more concerned about than absorption regarding drug distribution?

Back 3

Bioavailability

Front 4

What is Bioavailability? What symbol is commonly used for it?

Back 4

F = The fractional extent to which a dose of drug reaches its actual site of action or biological fluid that has access to the site of action.

Front 5

Equation for F:

Back 5

Amount in circulation
F = ---------------------
Amount administered

Front 6

What is the First Pass Effect?

Back 6

A reduction in the bioavailability of a drug due to metabolism and/or biliary excretion by the liver.

Front 7

What is the most common methid of drug administration?

Back 7

Oral

Front 8

What are 3 advantages of oral administration?

Back 8

-Safest
-Most convenient
-Most economical

Front 9

Disadvantage of oral administration:

Back 9

Oral drugs almost never have a complete bioavailability

Front 10

What drugs have a bioavailability of 1?

Back 10

IV drugs

Front 11

What are 2 reasons for which the F of oral drugs is never 1?

Back 11

-Incomplete absorption
-First pass effect

Front 12

What makes 2 drugs BIOEQUIVALENT?

Back 12

-Having the same ACTIVE INGREDIENT
-Work at the same AMOUNT
-Same ROUTE OF ADMINISTRATION
-Have the same EXTENT and RATE of entering the circulation

Front 13

What is the concept of Bioequivalence used for?

Back 13

Comparing formulations of drugs (generic)

Front 14

How are Orally administered drugs absorbed into the circulation?
-Mechanism
-From what site

Back 14

Mainly via Passive Diffusion from the GI tract

Front 15

What form of weak Acids/Bases are preferentially absorbed into the circulation?

Back 15

-Weak acids in the HA form
-Weak Bases in the B form

Front 16

So in general what does a drug have to be in order to be absorbed into the circulation?

Back 16

Nonionized

Front 17

Where in the GI tract are oral drugs predominantly absorbed?

Back 17

From the upper intestine

Front 18

What are 2 factors that limit drug absorption from the stomach?

Back 18

-Thick mucous lining
-Small surface area

Front 19

Why does the upper intestine allow for the majority of oral drug absorption?

Back 19

Villi provide very large SA

Front 20

What drugs will be nonionized in the stomach?

Back 20

Weak acids

Front 21

What happens to weak acids when they get into the upper intestine?

Back 21

They become ionized due to the higher pH (7)

Front 22

Does pH change the fact that even weak acids are absorbed more from the upper intestine than the stomach?

Back 22

no

Front 23

How does the concentration gradient favor absorption of weak acids from the upper intestine, if the amount of nonionized HA is so low there?

Back 23

The bloodflow continues to sweep away what little bit of HA gets absorbed, so the concentration gradient is maintained and favors absorption into circulation.

Front 24

What is a very important factor that influences absorption of oral drugs into circulation?

Back 24

Gastric emptying

Front 25

How does increased gastric emptying effect drug absorption?

Back 25

It increases it

Front 26

How does taking a drug with food affect gastric emptying and drug absorption?

Back 26

Food accelerates gastric emptying and absorption.

Front 27

What would be a reason for taking a drug on an empty stomach?

Back 27

If the drug had a short half life and you want to increase the duration of its effectiveness

Front 28

What does the rate of solid drug prep absorption depend on?

Back 28

The dissolution of the tablet in the GI tract fluid.

Front 29

4 types of solid drug formulations:

Back 29

-Controlled release
-Extended release
-Sustained release
-Prolonged action

Front 30

What are 2 advantages of controlled release?

Back 30

-Slower absorption so less frequent doses are necessary
-More uniform drug concentration in the blood

Front 31

What are 2 disadvantages of controlled release preparations?

Back 31

-There is greater variability in patients
-Can be toxic if the response in some patient is for the drug to all release at once

Front 32

For what type of drug is controlled-release formulation most logical?

Back 32

A drug with a short half life

Front 33

What are 2 functions served by Enteric coatings?

Back 33

1. Protects the drug from stomach acid dissolution
2. Protects the stomach from the drug

Front 34

What don't drug companies want enteric coatings to be?

Back 34

Completely impervious - or else the drug won't get absorbed at all in the intestine

Front 35

What is the reason for sublingual administration drugs?

Back 35

Immediate drainage to the superior vena cava

Front 36

Why is veinous drainage to the superior vena cava good?

Back 36

It bypasses the liver and protects the drug from immediate first pass effects.

Front 37

What is the most useful type of drugs for sublingual administration, and why?

Back 37

Highly lipophilic drugs - because the surface area in the mouth is small

Front 38

What is a specific example of a drug that is given sublingually?

Back 38

Nitroglycerin

Front 39

For what patients is rectal administration most useful?

Back 39

-Peds
-Unconscious
-Vomiting

Front 40

What is an advantage of rectal administration?

Back 40

50% of the drug bypasses the liver, so Less first pass effect than oral

Front 41

What are the 3 main disadvantages of rectal administration?

Back 41

-Absorption is variable
-Absorption can be incomplete
-The drug may irritate the rectal mucosa causing discomfort

Front 42

What does a drug have to be in order to be able to be administered transdermally? Why?

Back 42

Lipophilic - because the epidermis is a lipid barrier.

Front 43

What type of skin is most permeable for transdermal drug administration?

Back 43

Hydrated

Front 44

What is often done for transdermal absorption?

Back 44

Putting the drug into an occlusive dressing to maintain hydration of the skin.

Front 45

3 specific examples of drugs that are often administered Transdermally:

Back 45

-Nicotine
-Estrogen
-Progesterone

Front 46

What does Parenteral mean?

Back 46

Without the intestine (around it)

Front 47

What are the 3 types of parenteral injection?

Back 47

-Intravenous
-Subcutaneous
-Intramuscular

Front 48

What makes Intravenous injection unique from the other 2 types?

Back 48

It requires no absorption so its Bioavailability is 1

Front 49

How does drug that is injected subcutaneously or intramuscularly get into the circulation?

Back 49

By simple diffusion from the injection depot to nearby capillaries

Front 50

What 2 factors determine the rate of absorption of lipophilic drugs into nearby capillaries when given via subcu or intramuscular injection?

Back 50

1. Drug solubility in ISF
2. Area of the capillary bed

Front 51

How do large hydrophilic drugs get absorbed into capillaries?

Back 51

Via large aqueous channels in the endothelial cell membranes.

Front 52

How are Proteins that are administered via subcu or intramusc injection absorbed into circulation?

Back 52

Via slow entry into the lymphatic system

Front 53

What is an example of protein injections?

Back 53

Antigens for immunization

Front 54

To what tissue do parenterally administered drugs distribute first after they're absorbed into the circulation?

Back 54

The lungs

Front 55

What 3 processes can occur when parenterally administered drugs circulate to the lungs?

Back 55

-Metabolism
-Excretion of volatile agents
-Filtration of particulate matter

Front 56

What can the lungs do with lipophilic drugs?

Back 56

Store temporarily, then redistribute to other organs.

Front 57

The bioavailability of intravenously injected drugs is:

Back 57

100%!! F=1

Front 58

What are the 4 advantages of intravenous drug delivery?

Back 58

1. Drug delivery is controlled
2. Drug delivery is accurate
3. See an immediate response
4. Dose can be altered rapidly as needed

Front 59

What are 2 types of drugs for which IV adminstration is good?

Back 59

-Anesthetics
-Emergency treatments
-Irritating agents

Front 60

What are 2 reasons for which IV administration of more irritating drugs is good?

Back 60

-The irritant gets diluted within the whole blood volume
-The drug can be delivered more slowly

Front 61

What are 2 rates at which IV drug administration can be given?

Back 61

-Slow infusion
-Bolus

Front 62

What is a Bolus?

Back 62

When the entire volume to be administered is given very rapidly

Front 63

What are 2 disadvantages of IV drug administration?

Back 63

-It is the route of no return and is unforgiving of mistakes
-Requires close patient monitoring, a patent vein, and an experienced medical staff

Front 64

What drugs are appropriate for subcutaneous administration?

Back 64

Only drugs that are NONirritating, not painful, and not tissue-damaging.

Front 65

What is given along with a subcutaneous drug, if the desire is for the drug to act locally?

Back 65

A vasoconstrictor - to reuce capillary absorption.

Front 66

What 2 factors does intramuscular absorption depend on?

Back 66

-Bloodflow to the muscle
-Fat content of the muscle

Front 67

What is intramuscular absorption enhanced by?

Back 67

Exercise

Front 68

3 novel methods of drug delivery:

Back 68

-Drug eluting stents
-Targeting drugs via antibodies
-Prodrugs

Front 69

How do drug eluting stents work?

Back 69

By bloodflow elution of a drug place into a blood vessel

Front 70

How does antibody-coupling drugs target them to specific sites of action?

Back 70

The protein-binding domain of the Ab is pointed outward and binds to the target tissue

Front 71

How can drugs be made as prodrugs?

Back 71

By coupling them to polymers which keep the drug inactive until it reaches a specific site where it gets activated.