Parenteral & Transdermal Route of Adminstration Flashcards Preview

Pharmacy Year 3 > Parenteral & Transdermal Route of Adminstration > Flashcards

Flashcards in Parenteral & Transdermal Route of Adminstration Deck (35)
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1
Q

Describe the properties of intravenous injections

A
  • usually aqueous buffer at neutral pH
  • completely solubilised
  • no particles except for some nutritional lipids
  • hypertonic solutions are possible with slow administration
2
Q

What is intramuscular delivery suitable for?

A

Prolonged release of oily and particulate doses

3
Q

What is the benefit of higher blood flow in intramuscular drug delivery?

A

Higher absorption

4
Q

What are the advantages of subcutaneous drug delivery?

A
  • rapid and predictable
  • used for self-medication
  • used for poorly absorbed and fragile drugs
5
Q

What are the uses of intra-peritoneal drug delivery?

A

Chemotherapy for abdominal tumours, dialysis in renal failure or for diagnostic imaging agents

6
Q

Give a use for intrathecal drug delivery

A

Diagnostics - tumours in sub-arachnoid space

7
Q

Where are intracisternal drugs delivered to and what are the risks?

A

Space around the base of the brain

There is a risk of neurological injury or death by herniation if intracranial pressure is high

8
Q

Give uses for intra-ventricular drug delivery

A

Infection OR to reduce side effects in malignancy

9
Q

How do needle free injections work?

A

They force the drug through the skin - they can be spring powered or high pressure gas

10
Q

How do microneedle patches work?

A

The stratum corner is pierced with short needles to deliver drugs into the skin with minimal invasion. They increase skin permeability by creating micron-scale pathways in the skin - this actively drives drug through.
Can reach the epidermis too.

11
Q

What is the dosage range for transdermal formulations?

A

5-25mg daily

12
Q

How can transdermal drug penetration be enhanced?

A

through drug & delivery vehicle modification or through modification of the stratum corneum

13
Q

Give examples of powered penetration enhancement devices

A

Iontophoresis
Phonphoresis
Electroporation patches

14
Q

What are the routes of transdermal penetration?

A
  1. Directly across the stratum corneum
  2. Through sweat ducts
  3. Through hair follicles and sebaceous glands
15
Q

What are the properties of the stratum corneum?

A
  • 10-15µm dry
  • 40µm hydrated
  • layers of keratin rich corneocytes in an intercellular lipid matriculates extruded by keratinocytes
  • extruded lipid phase behaviour is different from biomembranes
16
Q

What is the major route for most drugs?

A

Intercellular route

Route for drugs soluble in lipid regions or in formulation disrupting the lipid regions

17
Q

What is the route for most hydrophilic drugs?

A

Transcellular
Hydrophilic drugs penetrate the aqueous regions of keratin filaments - but also have to go through intercellular lipid region.

18
Q

What is the ideal molecular weight for a transdermal patch?

A

<500 Da

but can have <1000 Da

19
Q

What is the ideal melting point for a transdermal patch?

A

<200°C

20
Q

What is the ideal LogP for a transdermal patch?

A

Between 1 and 3

21
Q

What is the ideal kinetic half life for a transdermal patch?

A

<6-8 hours

22
Q

What is the maximum patch size?

A

50cm2

23
Q

How can a drug vehicle be modified to enhance skin permeation?

A
  • Drug selection
  • Use of pro-drug
  • Ion pairs, complexes
  • Modification of chemical potential
  • Form a eutectic system
  • Use liposomes or vesicles
24
Q

When would you need to modify the stratum corneum?

A

If the drug doesn’t have ideal physicochemical properties

25
Q

How can the stratum corneum be modified to enhance skin permeation?

A

Hydration
Lipid fluidisation
Bypass / removal
Powered electrical devices

26
Q

What happens when a drug is at its highest thermodynamic activity?

A

It has maximum skin penetration

27
Q

What happens when water is taken up from the skin into the vehicle?

A

If water is taken up from the skin into the vehicle and acts as a an anti-solvent, thermodynamic activity of the permeant increases drug flux by 5-10X

28
Q

What is a eutectic mixture?

A

2 components at a certain ratio inhibit crystalline process of each other so that the melting point is less than it would be alone

29
Q

What is the benefit of having a lower melting point?

A

The greater the solubility in a given organic solvent

30
Q

Define enhancement ratio (equation)

A

Drug permeability coefficient after enhancer treatment / drug permeability coefficient before enhancer

31
Q

How can permeation be increased through modification of the stratum corneum?

A
  • Disruption og intercellular lipid lamellar structure
  • Interaction with intracellular proteins of the stratum corneum
  • Improvement of partitioning of a drug, with co-enhancer or co-solvent penetrating stratum corneum.
32
Q

How does hydration of stratum corneum improve permeation?

A

Alters drug solubility and partitioning. It increases skin hydration, swelling and opening the stratum corneum which leads to increased penetration

33
Q

How do liposomes improve permeation in the stratum corneum?

A

They hydrate/alter lipid layers

Deformable liposomes have solvent or surfactants to improve stability allowing them to squeeze through channels

34
Q

How does keratin and lipid disruption improve permeation?

A

The stratum corneum is disordered
Done by:
- mixing homogeneously with lipids, changing solubility
- extracting lipids forming aqueous channels or forming microcavities within the lipid

35
Q

What is the effect of shifting the solubility parameter on permeation?

A

Shifting the solubility parameter of the skin closer to the drug increases solubility and so increases drug permeation.