ADME Two

Question 1

What does drug absorption refer to?

Answer 1

The passage of drug from the site of administration into the circulation

Question 2

What administration technique results in immediate absorption?

Answer 2

Intravenous injection (100% absorbed)

Question 3

What sort of administration is difficult for absorption?

Answer 3

Orally taken drugs have to overcome several barriers so are often are delayed and incompletely absorbed

Question 4

What are two key factors of absorption?

Answer 4

Rate and Extent?

Question 5

What is meant by rate with regards to absorption?

Answer 5

How rapidly does the drug get from the site of administration to the general circulation?

Question 6

What is meant by extent in regards to absorption?

Answer 6

How much of the drug administered enters general circulation (% bioavailibility)

Question 7

What are the types of drug adminstration?

Answer 7

Enteral

• Oral (po)
• Sublingual
• Rectal

Parenteral

• IV
• IM
• Subcutaneous
• Intradermal
• Lungs

Question 8

What are the two most common routes of adminstration

Answer 8

IV (Rate = immediate, extent=100%)

Oral (Rate=gradual, extent=incomplete)

Question 9

What are the advantages of IV administration?

Answer 9

• Very rapid
• Precise control (100% Bioava)
• Avoids problems with absorption, drug breakdown before entering circulation
• Good for drugs that are too irritating to be taken by mouth or given by tissue injection

Question 10

What are the disadvantages of IV administration?

Answer 10

Skill required (dont want air embolism)
Careful preparations of injected material (sterile etc)
Most hazardous

Question 11

What are the advantages of oral administration?

Answer 11

80% drugs do this

Safest, most convenient and economic

Question 12

What are the disadvantages of oral administration?

Answer 12

Slow (0.5 to 3 hrs for effect)

Unpredictable with regards to Rate, Extent, Reproducibility

Question 13

What are the three steps of drug tablet consumption?

Answer 13

Disintegration
Dissolution
Absorption

Question 14

What are the drug factors influencing the oral bioavailibility of drugs?

Answer 14

Decomposition in acid gastric juices
Decomposition by gut enzymes
Degradation by gut microorganisms
Food may alter absorption rate and amount
Metabolism by gut wall enzymes
Metabolism by liver enzymes before entering systemic circulation

Question 15

What is the rate limiting step of drug passing through the gi tract?

Answer 15

The stomach, as does not get absorbed here but depends on gastric emptying rate

Question 16

What are the patient factors influencing absorption?

Answer 16

Stomach emptying rate
Intestinal motility
Interactions with food

Question 17

how does stomach emptying rate influence absorption?

Answer 17

Major factor!
Rate increased with hunger
Rate decreases with vigorous exercise, food, pain

Question 18

How does intestinal motility influence absorption?

Answer 18

Increased motility due to gastroenteritis and diarrhoea
-This decreases transit time (important for drugs with low water solubility)
Decreased motility with various drugs (Narcotics)

Question 19

How does interactions with food change absorption?

Answer 19

e.g Chelation of tetracycline with metal ions (ca)

Question 20

How do capillaries influence drug movement?

Answer 20

Most capillaries are relatively porous- thus drugs leave the blood regardless of whether they are poorly lipid soluble, charged or polar

Question 21

What is the exception to the capillary factor?

Answer 21

The bbb has no pores, and glia cells for protection, thus only lipid soluble drugs diffuse across the BBB, unless a drug undergoes active transport.

Question 22

How does blood flow influence drug distribution?

Answer 22

The tissues that receive more blood receive more drug.

Rate of distribution to tissues depends on blood flow rate. ie liver, lungs, heart receive drugs rapidly, muscles do not.