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PHA 333 > bio adhesive systems > Flashcards

bio adhesive systems Flashcards

1
Q

define bioadhesion

A

The attachment or association of a drug carrier system to a

biological surface, for extended periods of time

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2
Q

define a drug carrier system

A

any pharmaceutical dosage form

containing a bioadhesive polymer or ligand

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3
Q

what is a bioogical surface?

A

– Mucus layer lining the biological membrane - mucoadhesion

– Epithelial cells beneath the mucus - cytoadhesion

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4
Q

how is the mucous membrane made uo?

A
  • Epithelial cell layer covered by mucous layer

* Single cell layer or stratified multilayer

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5
Q

what is mucus?

A
  • Secreted by goblet cells or specialised glands
  • Viscoelastic gel matrix of mucin glycoproteins
  • Mucus thickness varies: 50-450 μm in stomach; < 1 μm in mouth
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6
Q

how long does it take for mucus turnover?

A
  • Variable ~ 4-5 hours

* Affects residence time of mucoadhesive formulation

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7
Q

what is the nature of a mucoadhesive bond?

A

• Non-specific interactions between mucus and
mucoadhesive polymer
• Physical or mechanical interactions
• Chemical bonds

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8
Q

what are the type of chemical bonds in a mucoadhesive bond?

A
  • Ionic bonds (mucus is -ve charged)
  • H-bonds
  • Van der Waal’s interactions
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9
Q

what are the different types of mucoadhesive polymers?

A

hydrogela

hydophobic polymers

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10
Q

how is a hydrogel made up? how is it delivered?

A

Hydrophilic polymers with swelling capacity
• e.g. Carbopols, chitosan (+ve charged), sodium alginate, cellulose derivatives
• Buccal / nasal delivery
• Most popular mucoadhesive polymers

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11
Q

how is a hydrophobic polymer made up? what route of delivery is it given by?

A
  • Non-swellable
  • e.g. polylactic acid (PLA)
  • Oral delivery
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12
Q

how do hydrophilic functional groups bond?

A
  • Form H-bonds or ionic bonds with the mucus layer

* Water uptake results to polymer swelling and chain disentanglement

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13
Q

what are the different types of hydrophilic functional groups and how do they bond?

A
  • Anionic polymers
  • H-bonding interaction with mucin
  • E.g. Carbomer
  • Cationic polymers
  • Ionic and H-bonding interaction with mucin
  • E.g. Chitosan
  • Non ionic
  • H-bonding interaction with mucin
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14
Q

what are the properties of mucoadhesive hydrogels?

A

hydrophilic functional groups
high MW
cross-linked networks

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15
Q

what is the optomum MW dor mucoadhesive hydrogels?

A

10,000 –4,000,000 Da

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16
Q

what happens if the MW is too high?

A 
slow hydration (swelling) and inadequate bond formation 
with mucus
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17
Q

what happens if the MW is too low?

A

excessive hydration, gel formation and complete

dissolution in mucus, loss of adhesive ability

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18
Q

what does the degree of cross linking affect?

A

swelling capacity and chain mobility

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19
Q

what may a high degree of cross linking cause?

A

may prevent over-hydration but may restrict chain mobility

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20
Q

what happens in the drug release process from mucoadhesive hydrogels?

A
  • Hydration of polymer and swelling of network

* Chain relaxation and diffusion of dissolved drug

21
Q

what occurs in cytoadhesion?

A 
• Cell-specific bioadhesion
– A recognition ligand is conjugated to the drug carrier 
system
– Useful for oral delivery
• Cell-specific ligands
– Lectins
– Bacterial adhesins
22
Q

what are lectins?

A

Proteins or glycoproteins that specifically recognise
and bind reversibly to specific carbohydrate residues
in the intestinal epithelium

23
Q

what are the properties of lectins?

A
  • Plant origin e.g. tomato lectin, asparagus pea lectin
  • Highly specific binding
  • Mucus may inactivate them
  • Bioinvasion
24
Q

what occurs in bioinvasion in lectins?

A
  • After binding, they undergo cellular uptake

* Facilitate intracellular transport of drug

25
Q

what are the benefits of bioadhesion to drug delivery?

A

• Enhanced bioavailability
• Prolonged residence time
• Decreased dosing frequency
• Increase in concentration gradient
• Target drug delivery to site of action or site of
absorption
• Localisation of the delivery system at a given target site

26
Q

how do you test mucoadhesive in vitro?

A

Force of attachment
– Measurement of adhesive strength between polymer and
substrate
• Rheological measurement

27
Q

what are the different locations of mucosal membranes?

A 
• GI tract
 Oral cavity (buccoadhesion)
 Oesophageal tissue
 Stomach
 Small / large intestine
• Nasal cavity
• Respiratory tract
• Ophthalmic (ocular) cavity
• Rectal cavity
• Vaginal cavity
28
Q

what are the advanatages of buccodhesive drug delivery?

A 
• Drugs with GI side effects 
or/and high metabolism
• High blood supply
• Robust epithelium
 No permanent damage
• Accessibility
• Resistant to removal by saliva 
flow and mechanical stress
29
Q

what are the disadvantages of buccoadhesive drug delivery?

A 
• Low permeability
 Skin < buccal cavity < small 
intestine
 Keratinised areas: gums, palates
 Non-keratinised areas: sublingual, 
cheeks
• Over-hydration of polymer by saliva
• Mucus and epithelial cell turnover
 5-6 days
• Accidental swallowing
30
Q

what are the dosage forms availible to buccoadhesive systems? how are they beneficial?

A

 Powder, tablets, patches, gels, pastes

 Non-irritant, small, flexible

31
Q

what are the local or systemic effects produced by buccoadhesive systems?

A

 Orahesive® powder, Orabase® paste

 Buccastem®, Suscard

32
Q

what are some examples of mucoadhesive hydrogels for buccadhesive systems?

A

 Carbopol, polycarbophil, penetration enhancer if required

33
Q

what are the advantages of nasal bioadhesive drug delivery?

A

• Drug with GI side effects or/and
with high 1st pass metabolism
• Accessibility
• Patient compliance

34
Q

what are the disadvantages of nasal bioadhesive drug delivery systems?

A 
• Low permeability
• Mucociliary clearance
• Turn-over time for mucus is 10-15 
minutes.
• Epithelial damage by penetration 
enhancers
35
Q

what are the dosage forms availible in nasal bioadhesive systems?

A

 Viscous solutions, gels, powders, polymeric microparticles

36
Q

what are the local or systemic effects in the nasal bioadhesive systems?

A

 Budesonide (nasal allergy)

 E.g. ketorolac (pain), antibiotics, vaccines, peptides

37
Q

what are some examples of mucoadhesive hydrogels for nasal bioadhesive systems?

A

 Carbopol, chitosan, xanthan gum, HPMC derivatives

38
Q

what are the forms availible for roal bioadhesive delivery systems?

A

– Tablets, multiparticulate suspensions

39
Q

what are the availible muoadhesive dosage forms for oral bioadhesive delivery systems?

A

– Hydrophobic polymer (non-swellable) e.g. poly lactic acid

– Hydrogels are not appropriate

40
Q

what are limitations of oral mucoadhesive dosage forms?

A

– Dosage form elimination

– Lack of specificity

41
Q

what use are cytoadhesive dosage forms?

A

– Targeting of specific sites in the GI tract
• Area of maximum absorption
• Area where a local effect may be required

42
Q

what is oesophageal delivery systems used for?

A

anti reflux therapy

anticancer therapy

43
Q

what are the advantages of vaginal mucoadhesive systems?

A 
• Avoidance of 1st pass 
metabolism
• Large surface area
• Rich blood supply
• Mucoadhesive formulations 
increase retention
44
Q

what are the disadvantages of vaginal delivery systems?

A 
Clearance by vaginal fluids
 Poor retention
• Variable thickness of vaginal 
epithelium 
 Rate and extent of absorption
• Potential mucosal irritation and 
damage to epithelium
45
Q

what are the systemic or local effects for the vaginal mucoadhesive systemms?

A

Local: microbiocides for HIV prophylaxis, labour inducers
(e.g. Prostin E2®), contraceptive (e.g. BufferGel®),
antimicrobial (e.g. Canesten)
 Systemic: treatment of STD, vaccine delivery, treatment
of cervical neoplasias

46
Q

what are the advantages of rectal mucoadhesive systems?

A 
Avoidance of 1st pass metabolism
 When drug is absorbed by 
inferior rectal veins 
• Large surface area (300 cm2)
• Rich blood supply
• Mucoadhesive formulations 
increase retention
47
Q

what are the disadvanatges of rectal ?

A

• Potential mucosal irritation

and damage to epithelium

48
Q

what are the local or systemic effect?

A

Local: constipation, haemorrhoids, ulcerative colitis

 Systemic: anticonvulsant therapy

PHA 333 (42 decks)

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