Administering Drugs by The Parenteral and Topical Route

Question 1

What is parenteral drug administration?

Answer 1

Administered by any route other than via the gastro-intestinal tract

Question 2

Give exams of parenteral routes

Answer 2

Intravenous 
Intradermal 
Intra-arterial 
Inhaled 
Subcutaneous 
Intrathecal 
Nasal mucosa 
Intramuscular 
Epidural 
Topical/transdermal

Question 3

What are the 4 layers of skin?

Answer 3

Epidermis
Dermis
Subcutaneous tissue
Muscle

Question 4

What degree is an intramuscular injection administered at?

Answer 4

90 degrees

Question 5

What degree is a subcutaneous injection administered at?

Answer 5

45 degrees

Question 6

What degree is an intravenous injection administered at?

Answer 6

25 degrees

Question 7

What degree is an intradermal injection administered at?

Answer 7

10-15 degrees

Question 8

What is intrathecal?

Answer 8

Through CSF

Question 9

Why would subcutaneous injections be used?

Answer 9

Most commonly used for insulin (for example).
The absorption is predictable
There is limited space in the subcutaneous tissue so small volumes only.

Question 10

When would intradermal route be used?

Answer 10

The skin has dendrite cells which provoke an immune response.
Used in allergy tests vaccination

Question 11

When would the intramuscular route route be used?

Answer 11

Larger volumes of drugs can be administered
It has predictable and rapid absorption
For example adrenaline in an allergic reaction
Because the muscle has good blood supply

Question 12

Why would the intravenous route be used?

Answer 12

It gives the fastest absorption into the blood. As it goes directly into the systemic circulation, by passing first pass metabolism.

Question 13

Disadvantage of the intravenous route?

Answer 13

It requires a cannula or IV catheter so it can’t be used outside of a healthcare setting.

Question 14

List the patient factors that alter the absorption of drugs after an injection:

Answer 14

Area/volume for absorption
Vascularity (blood supply to target region)
pH
Heath statutes of patient (ie. co-morbidities)
If they are taking other substances this could compete for the same absorption mechanism

Question 15

List the drug factors that alter the absorption of drugs after an injection:

Answer 15

Lipid and water solubility 
Molecular size 
Molecular charge 
Concentration 
Formulation

Question 16

What are topical drugs?

Answer 16

Drug delivery to an external body surface that can provide a localised or systemic effect

Question 17

Why can’t insulin be taken orally?

Answer 17

Insulin is a peptide, if taken orally it would be destroyed by digestive gut enzymes (protease).

Question 18

Why aren’t all drugs administered orally?

Answer 18

• Due to drug pharmacological, biological and chemical properties.
• The risk of significant systemic side effects.

Question 19

Examples of systemic topical drug administration:

Answer 19

• sublingual
• Transdermal
• Patch
• Inhalation
• Rectal

Question 20

Give examples of local topical drug administration:

Answer 20

• Creams/ointments
• Intranasal sprays
• Ocular drops

Question 21

What are the two affects that topical drugs can achieve?

Answer 21

Systemic

Local

Question 22

Topical administration to produce a systemic effect?

Answer 22

The drug is applied to a localised area of body surface, this minimises systemic side effects.

For example topical steroid for eczema.

Question 23

Topical administration to produce a systemic effect ?

Answer 23

The drug is applied to a body surface, provides an alternative and more convenient route into the blood.
For example Fentanyl patch

Question 24

What are the key formulation points?

Answer 24

• Target site
• Drug properties
• Acceptable to patient?

Question 25

What is the stratum corneum?

Answer 25

The principle barrier to penetration, a lipid multiple layered barrier.

Question 26

What are lipophilic drugs?

Answer 26

They use the intracellular route (readily cress cell walls, lipid drugs are absorbed)

Question 27

What are hydrophilic drugs?

Answer 27

The use the intercellular route.

Question 28

Ointment types?

Answer 28

Non-emulsifying, lipophilic

Water soluble, lipophilic and hydrophilic

Question 29

What are non emulsifying ointments and a disadvantage?

Answer 29

-contain beeswax and paraffin

Messy and inconvenient

Question 30

What are water soluble ointments and an advantage of using them?

Answer 30

They allow passage of drugs into the skin.

They are easily washed off

Question 31

Cream formula:

Answer 31

Lipophilic or hydrophilic
It penetrates rage stratum corneum
It’s water content allows it to rubbed into the skin (may provide soothing effect)
Contains preservative.

Question 32

Disadvantage of cream formula?

Answer 32

They contain preservatives so there is a risk of immunological sensitisation.

Question 33

Why is it important not to substitute drug formulations ?

Answer 33

Substituting an ointment fir a cream for example may provide different effects.

Question 34

The advantages of using a topical route:

Answer 34

• Alternative route if oral isn’t possible due to patient/drug factors
• Avoids first pass metabolism
• Targets the intended site of action
• Reduced risk of systemic side effects
• can generally be more accepted by patients

Question 35

The disadvantage of using topical route:

Answer 35

• slow absorption can be unpredictable
• can still produce side effects, there is still some systemic absorption.
• May be messy or inconvenient
• Rapid clearance of the drug so may require regular administration
• Formulation may cause side effects

Question 36

What is transdermal application?

Answer 36

Delivery system that releases drug through a rate controlling membrane into the skin, into the systemic circulation.

• Time released delivery
• Lipid soluble drugs

Question 37

Advantage of transdermal application?

Answer 37

Avoids fluctuation in plasma concentration

• Avoids first pass metabolism
• Easy to administer and acceptable to patients
• Can be stopped easily
• Prolonged drug action (less peak and troughs in the curve)
• can avoid gastrointestinal incompatibility

Question 38

Disadvantage of transdermal application?

Answer 38

• Only small enough molecules can penetrate the skin this way -Not applying patch appropriately will affect the dose
• Local Side effects -Skin irritation
• Slow initiate effects
• Only useful for drugs which require small concentration (potent) to get an effect.