Administering Drugs by The Parenteral and Topical Route Flashcards
What is parenteral drug administration?
Administered by any route other than via the gastro-intestinal tract
Give exams of parenteral routes
Intravenous Intradermal Intra-arterial Inhaled Subcutaneous Intrathecal Nasal mucosa Intramuscular Epidural Topical/transdermal
What are the 4 layers of skin?
Epidermis
Dermis
Subcutaneous tissue
Muscle
What degree is an intramuscular injection administered at?
90 degrees
What degree is a subcutaneous injection administered at?
45 degrees
What degree is an intravenous injection administered at?
25 degrees
What degree is an intradermal injection administered at?
10-15 degrees
What is intrathecal?
Through CSF
Why would subcutaneous injections be used?
Most commonly used for insulin (for example).
The absorption is predictable
There is limited space in the subcutaneous tissue so small volumes only.
When would intradermal route be used?
The skin has dendrite cells which provoke an immune response.
Used in allergy tests vaccination
When would the intramuscular route route be used?
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
Why would the intravenous route be used?
It gives the fastest absorption into the blood. As it goes directly into the systemic circulation, by passing first pass metabolism.
Disadvantage of the intravenous route?
It requires a cannula or IV catheter so it can’t be used outside of a healthcare setting.
List the patient factors that alter the absorption of drugs after an injection:
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
List the drug factors that alter the absorption of drugs after an injection:
Lipid and water solubility Molecular size Molecular charge Concentration Formulation
What are topical drugs?
Drug delivery to an external body surface that can provide a localised or systemic effect
Why can’t insulin be taken orally?
Insulin is a peptide, if taken orally it would be destroyed by digestive gut enzymes (protease).
Why aren’t all drugs administered orally?
- Due to drug pharmacological, biological and chemical properties.
- The risk of significant systemic side effects.
Examples of systemic topical drug administration:
- sublingual
- Transdermal
- Patch
- Inhalation
- Rectal
Give examples of local topical drug administration:
- Creams/ointments
- Intranasal sprays
- Ocular drops
What are the two affects that topical drugs can achieve?
Systemic
Local
Topical administration to produce a systemic effect?
The drug is applied to a localised area of body surface, this minimises systemic side effects.
For example topical steroid for eczema.
Topical administration to produce a systemic effect ?
The drug is applied to a body surface, provides an alternative and more convenient route into the blood.
For example Fentanyl patch
What are the key formulation points?
- Target site
- Drug properties
- Acceptable to patient?
What is the stratum corneum?
The principle barrier to penetration, a lipid multiple layered barrier.
What are lipophilic drugs?
They use the intracellular route (readily cress cell walls, lipid drugs are absorbed)
What are hydrophilic drugs?
The use the intercellular route.
Ointment types?
Non-emulsifying, lipophilic
Water soluble, lipophilic and hydrophilic
What are non emulsifying ointments and a disadvantage?
-contain beeswax and paraffin
Messy and inconvenient
What are water soluble ointments and an advantage of using them?
They allow passage of drugs into the skin.
They are easily washed off
Cream formula:
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.
Disadvantage of cream formula?
They contain preservatives so there is a risk of immunological sensitisation.
Why is it important not to substitute drug formulations ?
Substituting an ointment fir a cream for example may provide different effects.
The advantages of using a topical route:
- 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
The disadvantage of using topical route:
- 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
What is transdermal application?
Delivery system that releases drug through a rate controlling membrane into the skin, into the systemic circulation.
- Time released delivery
- Lipid soluble drugs
Advantage of transdermal application?
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
Disadvantage of transdermal application?
- 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.