Drug Handling Of The Body

Question 1

What are the advantages of oral administration?

Answer 1

Convenient for patient

Absorption from small intestine- large surface area

Question 2

What are the disadvantages of oral administration?

Answer 2

Not appropriate for all patients
Absorption can be variable 
Absorption can depend of stomach contents
Rate of gastric emptying 
Degradation in the stomach
First pass metabolism

Question 3

What does degradation in the stomach mean?

Answer 3

Parenteral cells secrets HCL

Chief cells secrete digestive enzymes this means the drug could have low bioavailability

Question 4

What does bioavailability mean?

Answer 4

The amount of drug that reaches the circulation as intact drug

Question 5

Want does first pass metabolism mean?

Answer 5

Drug gets lost in the liver due to hepatic first pass effect, low bioavailability

Question 6

What are the advantages of topical administration?

Answer 6

Convenient

Poorly absorption means minimum risks of overdosing

Question 7

What are the disadvantages of topical administration?

Answer 7

Negative effect on the skin- thinning of the skin

Question 8

What are the advantages of transdermal administration?

Answer 8

Long acting
Useful for when you want low blood levels for a long period of time
Suitable for a wide range of patient groups

Question 9

What are the disadvantages of transdermal administration?

Answer 9

Skin effects
Variable absorption
Lipid solubility 
Potent 
Expensive

Question 10

What are the advantages of rectal administration?

Answer 10

Local effect

Useful for patient who cannot swallow

Question 11

What are the disadvantages of rectal administration?

Answer 11

Need to be trained

Question 12

Example of rectal drugs

Answer 12

Analgesics
Diazepam
Prednisolone
Antifungals

Question 13

What are the advantages of inhalation?

Answer 13

Rapid changes in the plasma concentration of drug because of the high surface area of the lungs and good blood flow to area

Local or systemic effect

Question 14

What are the disadvantages of inhalation?

Answer 14

Difficulties in ensuring the drug reaches the site of action

Question 15

Example of inhalation drugs

Answer 15

Halothane
Salabutomol
Nitric oxide
GTN

Question 16

What are Parenteral routes?

Answer 16

IV- thiopental, heparin
IM-pre-Meds
Intradermal- dentistry, local anaesthesia, allergy screening
SC- insulin
INTRATHECAL- antiviral agents, chemo drugs
Epidural- nerve blockers used during labour

Question 17

What are the advantages of parenteral administration?

Answer 17

Rapid action
By pass stomach and liver
Lower doses is required
Patent controlled for analgesia- syringe drivers

Question 18

What are the disadvantages of Parenteral administration?

Answer 18

Trained person needed
Extreme care required
Accidental overdose?
IM- painful

Question 19

Explain the different types of formation of drugs

Answer 19

Tablets, gels, locations, aresols, suspensions. Powders. Granules. Capsules, lotions, patches, Inhalations, pastes, sprays, syrup, creams, gases

Can impact upon the bioavailability and sustained release

Question 20

Explain the oral drug absorption

Answer 20

From tablet to granules to fine particles to solutions, then absorbed through stomach and small intestine

Question 21

How does the drug cross the cell membrane?

Answer 21

If they are lipid soluble- can cross through the epithelial cell in the small intestine to get to the blood stream through diffusion

If water soluble cannot cross through

Question 22

How is the drug absorbed whole it moves across membranes?

Answer 22

1 passage through water channels
2 endocytosis
3 passive diffusion
4 facilitated of active transport

Question 23

What is facilities transport?

Answer 23

Drug moves down concentrated gradient
Proteins provide channels
No energy required
Staturable, selective, competitive inhibition by other substances

Question 24

What is active transport?

Answer 24

Drug moves against the concentration gradient
Energy is required
Saturable, selective, competition inhibition
Example:lithium, levodapa, methyldopa

Question 25

What happens when the drug has been absorbed?

Answer 25

Distributed via blood stream | Transferred into and out of various tissues in the body

Question 26

Want affects extent of distribution?

Answer 26

Lipid solubility of drugs Blood flow to organ/tissue Binging of drugs to proteins

Question 27

Explain the blood flow in these organs/tissues: liver, kidney, CNS, myocardium, fat, other I.e. Muscles

Answer 27

Liver: 680ml/min/kg Kidney: 3,333 ml/min/kg: received the most blood flow CNS: 615ml/min/kg Myocardium: 833ml/min/kg Fat and other: 25ml/min/kg each: here drugs are not distributed

Question 28

Where does protein binding occurs?

Answer 28

Free drugs can bind to proteins in the plasma I.e. Albumin | Only free drugs can diffuse across membranes and have an effect

Question 29

How is drug removed from the body?

Answer 29

Through metabolism and excretion Most drugs are lipophilic and so will recirculate around the body We excited water soluble drugs

Question 30

Define drug metabolism

Answer 30

It is the enzyme-mediated conversion of a lipid soluble compound into a more water soluble one, ready for excretion

Question 31

Where does metabolism take place?

Answer 31

``` Mainly in the liver : smooth endoplasmic reticulum Kidneys Lung GI tract Brain Plasma ```

Question 32

What are the phases of metabolism?

Answer 32

There are two phases. Usually occur in a sequence, phase 1 then phase 11, however phase 11 can precede phase 1

Question 33

What happens in phase 1?

Answer 33

Modify the chemical structure of drug Makes drugs slightly more water soluble Prepare for phase 11 Products can be more chemically reactive than the parent drug

Question 34

What are pro-drugs?

Answer 34

Some drugs when metabolised can even more active than the original drug Example: prednisone becomes prednisolone Codeine become morphine GTN becomes nitric oxide

Question 35

What happens on phase 11 of metabolism?

Answer 35

Conjugate drug into large molecules- amino acid, sulphate groups Product become water soluble and easily excreted Increased molecular weight Inactive , decrease receptor affinity and enhance excretion

Question 36

Explain a how drugs interact.

Answer 36

Drugs metabolising enzymes can be a) induced I.e alcohol and carbamazepine induce liver enzymes and b) inhibited such as fluoxetine and grape juice This will result in decrease of the duration of drug action

Question 37

Explain the role of excretion

Answer 37

Removal of drugs: drug metabolic and water soluble drugs Urine, bile, faeces, lungs, skin To increase drug exception, increase blood flow to the kidneys, decrease plasma protein binding

Question 38

Explain the dosage regimens

Answer 38

The therapeutic response of most drugs is related to the level of the drug in the plasma We need to know the half life of a drug, this is the time it takes for the amount of drug to decrease to one half of the peak level The rate at which drugs are eliminated from the body

Question 39

How much drug remains if the half life is 2hours for 20mg drug?

Answer 39

``` After 2 hours: 10mg drug will remain 4hrs: 5mg 6hrs: 2.5mg 8hrs: 1.25mg 10hrs: 0.625mg After 10 hrs sufficient to say all the drug has gone ```

Question 40

How much of the drug is eliminated in 5 half lives?

Answer 40

97%

Question 41

Why do we care about half lives?

Answer 41

To avoid drug interactions | Estimating how long it will take for toxic concentration to be eliminated from body

Question 42

What is drug disposition?

Answer 42

What the body does to the drug compared to what the drug does to the body Intake-->absoprtion-->distribution-->drug-cell interaction-->metabolism --> excretion

Question 43

Explain the therapeutic window

Answer 43

A range of doses that produces therapeutic response without causing any significant adverse effect in patients. Generally therapeutic window is a ratio between minimum effective concentrations (MEC) to the minimum toxic concentration (MTC). I.e. Warfarin and phenytoin have narrow therapeutic window and so need close monitoring

Question 44

What happens if a patient has renal or hepatic disease?

Answer 44

The plasma half life increase and drug concentrations may reach a toxic level