L32 - absorption: sublingual, buccal & rectal drug delivery
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is contact of most drugs with oral cavity brief?
yes as most drugs are swallowed
what is topical drug delivery to mouth used for?
ulcers, functor infections, periodontal disease
2 types of oral transmucosal delivery
• sublingual: under tongue • buccal: cheeks
what is the lining of the oral cavity?
oral mucosa (buccal, sublingual, gingival, labial, palatal mucosae)
what is gingival?
gums
SA of buccal + sublingual
~ 200cm cubed - smaller than SI
structure of oral mucosa
• stratified squamous epithelium in cell 2.lamina propria: contains blood vessels + nerve endings, so we need to get drug past this into systemic circulation. • basement memb + cells above = spread out as they age • prickle cells = lipophillic membrane coating granules, affects absorption of drugs
3 types of epithelium in mouth
• masticatory: gums + palatal • lining: buccal + sublingual • specialised: dorsal tongue
structure of masticator mucosal epithelium (gingival + palatal)
layer of keratin on outer layer of cells acts as barrier to drug absorption, so poor permeability - good residence time of palatal = sticks very well to it - gums have intermediate residence time
structure of lining epithelium?
no layer of keratin. - sublingual memb thinner so better permeability, bad residence time - buccal has intermediate residence time
permeability of masticatory epithelium
poor
permeability of lining epithelium
buccal = intermediate sublingual = very good
what pathway do lipophilic drugs pass through?
most common transceullar pathway via passive diffusion. • rate of drug absorption affected by epithelial thickness
what pathway do hydrophilic drugs pass through?
• paracellular (more common in MOUTH). • due to intracellular lipids from memb coating granules • epithelial thickness effects rate of drug absorption across memb
order of permeability
skin < oral mucosa < GI
what is the pH of oral cavity?
5.6-7.6 = small area + small volume of liquid in mouth so not much space for buffering
log P values of drugs via oral membranes
generally 1-5
what is saliva?
95% water + mucus, electrolytes, enzymes
why do we need saliva for drugs?
for drug to go in solution to be absorbed
enzymes in saliva
aminopeptidases, carboxypeptidases, esterases, carbohydrases (e.g amylase), lysozyme: fewer enzymes and lower activity than GI tract
what can saliva do to drug absorption?
• can aid or hinder it when drug is being deliver sublingually • saliva wash otu
what is mucus for drugs?
• physical barrier • negatively charged so can hinder absorption of positively charged drugs
blood supply in mouth
good blood flow
how does the buccal and sublingual route avoid hepatic first pass effect?
drug can go straight into systemic circulation