Gastrointestinal absorption Flashcards
Is the oral epithelium highly permeable?
No
What is the oral cavity rich in?
blood vessels & lymphatics
How do drugs evade first past metabolism when absorbed by the oral mucosa?
enter blood stream through jugular vein
What are the 8 disadvantages of oral mucosa drug delivery?
1) small moderately lipophilic molecules absorbed
2) very lipophilic molecules will not solubilise in saliva, poorly absorbed
3) polar molecules poorly absorbed (not penetrate oral mucosa)
4) dose form must be kept in place for time
5) total area of absorption low
6) lot of drug swallowed
7) taste must be bland
8) drug must be non irritant
What affects does the stomach have on the environment of the drug?
solubility, ionisation and stability of drugs
How does motility affect drug absorption?
presence of food, size of the meal as well as food or formulation components affect gastric emptying and therefore absorption
What are the steps for a drug to reach the apical of the enterocyte?
must dissolve in lumen, must bypass unstirred water layer & mucus and chemical & enzymatic stability in the lumen
Which molecules are good for entering the enterocyte?
small, stable, hydrophilic and ionised
How do molecules enter the enterocyte?
intercellular or transcellular
From Fick’s law which component determines whether a drug generates the membrane?
diffusion co-effcient
What are the most important physiochemical properties that determine the diffusion coefficient?
partition co-efficient (P) and molecular weight (MW)
What is the partition co-effcient?
how drug distributes between a pair of solvents when un-ionised
Which drugs have a high and low P
high - hydrophobic `
low - hydrophilic
Are drugs ionised or unionised when penetrating the lipophilic membrane?
unionised
