Drug Administration Flashcards
Define absorption:
The passage of a drug from its site of administration into the plasma
For what administration is absorption not a factor?
Intravenous injection
What is the absorption process in oral administration?
Little occurs until the small intestine
What is the absorption process in sublingual administration?
Absorption in the oral cavity
When would absorption through the oral cavity be useful?
If a rapid response is required
When you you use rectal or vaginal administration?
To produce a local effect
In epithelial application where is the drug normally applied?
The skin, the cornea of the eye or the nasal mucosa
What is administration to the skin otherwise known as?
Topical
When would you use inhalation as an administration?
For volatile substances
What are the four types of injection?
- Intravenous injection
- Subcutanous/intramuscular
- Intrathecal
- Epidural
What does it mean when you say drugs are weak electrolytes?
They are acids and bases that exist in an equillibrium of charged and uncharged forms
What form of the drug can cross the cell membrane?
Only the uncharged ones (hydrophobic) can cross the cell membrane
In acids, is the ionised form protonated or deprotonated?
Depronated (AH-)
In bases, is the ionised form protonated or deprotonated?
Protonated (BH+)
In acids, is the ionised form protonated or deprotonated?
Depronated (A-)
The ratio of uncharged to charge is dependent on what?
pH and pKA
How can you work out the ratio of charged to uncharged?
Using the Henderson Hasselbach Equation
What is the PKA
The dissociation constant: how easily it can pick up or lose an electron
If an acid has a ph thats one unit higher than the pka what will the ionisation be?
10:1 of ionised:unionised
If an acid has a ph thats two units higher than the pka what will the ionisation be?
100:1 of ionised:unionised
What are three advantages of oral administration?
- Easy and convenient administration
- No skilled personnel required
- No need for steralisation
If the stomach pH is 2 how well absorbed would an acidic drug be and how would you work this out?
An acidic drug would have a pKa of about 5 meaning if you take the inverse log you get a ratio of 1:1000 ionised:deionised meaning that the drugs are readily absorbed
If the stomach pH is 2 how well absorbed would a basic drugs be and how would you work this out?
Basic drugs have a ph of higher than 7 and therefore if you take the inverse log you would get a ratio of about 1:100000 deionised to ionised therefore these drugs would not be readily absorbed
If the stomach ph is 2 how well absorbed would neutral drugs be? What is an example of a neutral drug?
Readily absorbed and alcohol
What is an example of an acidic drug?
Aspirin
What is an example of a basic drug?
Amphetamine
If the duodenum has a ph of 8 will acidic drugs be readily absorbed? How do you work this out?
Since the pka of acidic drugs is about 5 the ratio of ionised to non-ionised is about 100:1 so is not readily absorbed
If the duodenum has a ph of 8 will basic drugs be readily absorbed? How do you work this out?
Basic drugs have a Ph normally above 8 so therefore will be have a higher ionised:deionised ratio and will be readily absorbed
Theoretically the duodenum should not absorbed acidic drugs, why is this?
It has an incredibly large surface area - major site of absorption for basic, acidic and lipophillic drugs
What are the disadvantages of using the oral route of administration?
Not fast acting and absorption may be incomplete
Tubocurraine cannot be given orally; why is this?
Is ionised throughout the ph range of the gut
Insulin cannot be given orally; why is this?
It is too large to be absorbed
What are some reasons why drugs cant be given orally?
They are destroyed by first pass effect in the liver after they are absorbed or are destroyed by enzymes, bacteria and acid in the gut
What kind of affects can inhaled drugs have?
Local or systemic
What is an example of a drug that is inhaled and gives a local effect? What could it be used to treat?
Salabutamol has an effect on the lung when inhaled used to treat asthma
What is an example of a drug that is inhaled and gives a systemic effect? What is it used for?
halothane is a general anesthetic
What is an advantage of using an injection as a route of administration?
They are not absorbed so by pass any difficulties associated with it
What are some disadvantages of injection that other administration routes don’t have?
The drugs have to be sterile and administered by skilled personnel
What is a very important factor when administering an injection?
The exact dose must be known
What is an intravenous injection?
Injection into the vein
What are three advtantages of intravenous injection?
- Irritant drugs can be used
- Large volumes can be used
- Rapid action
What is an disadvantage of intravenous injection?
You cannot recall the drug
What is subcutaneous/intramuscular administration?
Injection into the layer between tissue and muscle
What are three advantages of the subcutaneous route?
- Use a drug vehicle
- Oily - slow effect
- aqueous - rapid effect
What are the disadvantages of the subcutaneous route?
Can damage the site of injection and can only use small volumes
What are 6 important factors when it comes to deciding what kind of administration should be used?
- The chemical nature of the drug - looking at how it will be absorbed and if it will be irritant
- How quickly the effect is required i.e. for a fast effect you wouldnt use oral administration
- How long the effect should be maintained
- The patients condition
- The patients compliance
- Convienience - it would not make
What are 6 important factors when it comes to deciding what kind of administration should be used?
- The chemical nature of the drug - looking at how it will be absorbed and if it will be irritant
- How quickly the effect is required i.e. for a fast effect you wouldnt use oral administration
- How long the effect should be maintained
- The patients condition
- The patients compliance - not as important as sometimes decisions must be made for them if
- Convienience - of least important
How do the drugs get out of the plasma and into the tissues?
Through leaky pores in blood vessels allows them to get into the interstitial fluid
Why is drugs getting into the interstitial fluid important?
The interstitial fluid surrounds the tissues so the drugs can therefore interact with the target cells
Why might plasma protein binding affect drug distribution?
Because only the unbound protein can diffuse into the tissues and is therefore active
What is an extreme example of a drug that is highly bound to plasma proteins?
Warfarrin
What is different about the capillaries in the CNS? What barrier is this better known by?
They have no leaky pores. The blood brain barrier
What drugs can therefore cross into the CNS and what drugs cant?
Only lipophillic drugs can cross the membrane and ionised drugs and excluded
What is another example of a good barrier to drugs and what kind of drugs can cross it?
The placental barrier - only lipophillic drugs
What terminates the effect of drugs?
Distrubution of the drugs away from their site of action
What is an example of a drugs that would distrubute away from its site of action and therefore terminate its effect?
Local anasthetics e.g. lidocaine
How would you prevent drugs from distrubuting away from their site of action?
Keep them there using a vasnconstrictor such as adrenaline
