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PHA333 > bioadhasives > Flashcards

bioadhasives Flashcards

1
Q

What is 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

What is a drug carrier system?

A

any pharmaceutical dosage form containing a bioadhesive polymer or ligand

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3
Q

2 types of biological surfaces and their type of adhesion

A
  1. mucus layer lining the biological membrane - mucoadhesion

2. epithelial cells beneath the mucus - cytoadhesion

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4
Q

mucous membrane

A

epithelial cell layer covered by mucous layer

single cell layer or stratified multilayer

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4
Q

mucus

A

secreted by goblet cells or specialised glands

viscoelastic gel matrix or mucin glycoproteins

mucus thickness varies

  • 50-450 microm in stomach
  • <1 microm in mouth
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5
Q

mucous turnover

A

around 4-5hrs

affects resistance time of mucoadhesive formulation

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6
Q

nature of mucoadhesive bonds

A
  • non-specific interactions between mucous and mucoadhesive polymer
  • physical or mechanical interactions
  • chemical bonds
  • > ionic (mucous is -ve charged), H bonds, van der waals interactions
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7
Q

types of mucoadhesive polymers

A
  1. hydrogels

2. hydrophobic polymers

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8
Q

What are hydrogels?

A

hydrophilic polymer with swelling capacity

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9
Q

examples of hydrogels

A

carbopols
chitosan (+ve charge, can ionic bond)
sodium alginate
cellulose derivatives

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10
Q

type of delivery for hydrogels

A

buccal

nasal

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11
Q

most popular mucoadhesive polymer

A

hydrogels

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12
Q

What are hydrophobic polymers?

A

non-swellable

  • only van der waals interactions
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13
Q

example of hydrophobic polymer

A

polylactic acid (PLA)

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14
Q

type of delivery for hydrophobic polymers

A

oral delivery

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15
Q

properties of mucoadhesive hydrogels

A

hydrophilic functional group

high Mr

cross linked network

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16
Q

hydrophilic functional group of hydrogels

A

form H bonds or ionic bonds with the mucus layer

water uptake results in polymer swelling and chain disentanglement

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17
Q

3 types of hydrophilic functional groups of hydrogels

A
  1. anionic polymers - H bonding interaction with mucin, eg carbomer
  2. cationic polymers - ionic and H bonding interaction with mucin, eg chitosan
  3. non-ionic - H bonding interaction with mucin
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18
Q

high Mr of hydrogels

A
  • polymer chain length -> entanglement with mucin chains
  • optimin Mw = 10,000-4.000.000 Da
  • too high Mr - slow hydration and inadequate bond formation
  • too low Mr - excessive hydration, gel formation and complete dissolution in ucus, loss of adhesive ability
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19
Q

cross linked networks

A

degree of cross linking affects swelling capacity and chain mobility

high degre of cross linking may prevent over hydration but may restrict chain mobility

-> need partial cross linking, retains liquid behaviour so it can continue to interact

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20
Q

drug release process from mucoadhesive hydrogels

A
  • hydration of polymer and swelling of network

- chain relaxation and difusion of dissolved drug

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21
Q

What is cytoadhesion?

A

adhesion to cells

cell specific bioadhesion

  • a recognition ligand is attached to the drug carrier
  • useful for oral delivery

cell specific ligands

  • lectins
  • bacterial adhesins
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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

lectins characcteristics

A

plant origin
- tomato lectin, asparagus pea lectin (can interact with foods)

highly specific binding

mucus may inactivate them

bioinvasion

  • after binding, undergo cellular uptake
  • facilitate intracellular transport of drug
24
Q

benefits of bioadhesion drug delivery

A

enhanced bioavailability

  • prolonged residence time
  • dec dosing frequency
  • inc in conc gradient

target drug delivery to site of action or site of absorption
- localisation of the delivery system at a given target site

25
Q

mucoadhesive in vitro testing

A

force of attachment - measurement of adhesive strength between polymer and substrate

rheological measurement

26
Q

location of mucosal membranes in body

A 
GIT (oral, oesophageal tisue, stomach, small/large intestine)
nasal cavity
respiratory tract
ophthalmic (ocular) cavity
rectal cavoty
vaginal cavity
27
Q

advantages of buccoadhesive drug delivery

A
  • drugs with GI s/e and/or oral metabolism (bypasses GIT)
  • high blood supply
  • robust epithelium (no permanent damage)
  • accessibility
  • resistant to removal by saliva flow and mechanical stress
28
Q

disadvantages of buccoadhesive drug delivery

A
  • low permeability
  • > skin keratinised areas: gum, palates (barriers to absorption)
  • > non keratinised areas: sublingual, cheeks (good)
  • over hydration of polymer by saliva
  • mucus and epithelial cell turnover (5-6 days - long)
  • accidental swallowing
29
Q

dosage forms for buccoadhesive systems

A 
powder
tablet
patches
gels
pastes

-> non-irritant, small, flexible

30
Q

buccoadhesive systems for local effects

A

Orahesive powder

Orabase paste

-> for mouth ulcers

31
Q

buccoadhesive systems for systemic effects

A

Buccastem

Suscard

32
Q

mucoadhesive hydrogels for buccoadhesive systems

A

Carbopol
polycarbophil
penetration enhancer if required

33
Q

advantages of nasal bioadhesive drug delivery

A
  • drug with GI s/e and/or high 1st pass metabolism
  • accessibility
  • patient compliance
34
Q

advantages of nasal bioadhesive drug delivery

A
  • drug with GI s/e and/or high 1st pass metabolism
  • accessibility
  • patient compliance
35
Q

disadvantages of nasal bioadhesive drug delivery

A
  • low permeability
  • mucociliary clearance
  • turn over time for mucus is 10-15mins
  • epithelial damage by penetration enhancers

-> not the best form

35
Q

dosage forms of nasal bioadhesive systems

A

viscous solutions
gels
powders
polymeric microparticles

35
Q

local effects of nasal bioadhesive systems

A

budesonide for allergy

35
Q

systemic uses of nasal bioadhesive systems

A

ketotolac for pain
antibiotics
vaccines (nasalflu vaccine)
peptides

36
Q

mucoadhesive hydrogels for nasal bioadhesive systems

A

Carbopol
chitosan
xanthan gum
HPMC derivatives

37
Q

types of dosage forms for oral bioadhesive delivery systems

A

mucoadhesive or cytoadhesive dosage forms

  • tablets, multiparticulate suspensions
38
Q

**DELETE***

A

**DELETE**

39
Q

properties of mucoadhesive dosage forms for ORAL bioadhesive systems

A

hydrophobic polymer (non-swellable) eg poly lactic acis

-> hydrogels are NOT appropriate (dissolves easily in GIT, will lose adhesive effect, want to avoid this)

40
Q

limitations of oral bioadhesive dosage forms

A

dosage form elimination

lack of specificity

41
Q

advantage of cytoadhesive dosage forms for ORAL bioadhesive delivery systems

A

targeting of specific sites in GIT

  • area of max absorption (eg small intestine)
  • area where a local effect may be required
42
Q

2 therapies used in OESOPHAGEAL bioadhesive delivery systems

A
  1. anti-relfux therapy
    - sodium alginate mucoadhesive gel
    - protective layer adhered to oesophageal tissue
    - Gaviscon infant
  2. anti cancer therapy
    - localisation of Tx
42
Q

advantages of VAGINAL mucoadhesive systems

A
  • avoidance of 1st pass metabolism
  • large SA
  • rich blood supply
  • mucoadhesive formulations increase retention
43
Q

disadvantages of VAGINAL mucoadhesive 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
43
Q

dosage forms of vaginal mucoadhesive systems

A

gels
pessaries
creams
films

43
Q

LOCAL effects for VAGINAL mucoadhesive systems

A

microbiocides for HIV prophylaxis
labour inducers (Prostin E2)
contraceptive (BufferGel)
antimicrobial (Canesten)

43
Q

SYSTEMIC effects of VAGINAL mucoadhesive systems

A

treatment of STD
vaccine delivery
Tx of cervical neoplasias

44
Q

advantages of RECTAL mucoadhesive systems

A
  • avoidance of 1st pass metabolism (drug absorbed by interior rectal veins)
  • large SA (300cm sq)
  • rich blood supply
  • mucoadhesion formulations inc retention
45
Q

disadvantage of RECTAL mucoadhesive systems

A

potential mucosal irritation and damage to epithelium

46
Q

dosage forms of RECTAL mucoadhesive systems

A 
suppositories
gels
creams
films
thermoreversible mucoadhesive suppositories
47
Q

LOCAL effects of RECTAL mucoadhesive systems

A

constipation
haemorrhoids
ulcerative colitis

48
Q

SYSTEMIC effects of RECTAL mucoadhesive systems

A

anticonvulsant therapy

PHA333 (27 decks)

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