(18) Oral biopharmaceutics 1 Flashcards
(17 cards)
outline the mechanism of the transcellular route by passive diffusion.
• High concentration of drug on apical side of cell
• Low concentration inside the cell
• Molecule diffuses into cell and out the other side into intercellular area and the blood
- many lipophilic drugs and neutral molecules
what 4 ways can drugs be absorbed from the GI tract?
• Transcellular route by passive diffusion
• Transcellular route via active transport
• Transcellular route via facilitated diffusion
• Paracellular route (tight junctions)
what are the functions of the large intestine?
- limited absorption for drugs
- absorbs water
- absorbs lipids
- gut microbiome will metabolise many nutrients and drugs
what does the small intestine do?
- absorbs nutrients, salts + drug molecules.
what generally occurs in the stomach/
- mechanical digestion of food = peristalsis
- mixes the food with gastric juices = chyme
- this facilitates the absorption of nutrients
what is acid, pepsin and mucus in the stomach produced by? And what do they do?
- parietal cells (kills bacteria / aids breakdown)
- peptic cells (breaks down protein)
- mucosal cells (protects the stomach from auto digestion)
what is enterohepatic
• Bile salts are produced in the liver stored in the gallbladder
• They are released in the duodenum in the presence of food, where they act as surfactants and emulsifiers
• Most of the quantity of bile salts is reabsorbed (mainly in the ileum) and stored back in the gallbladder to be reused
what is the definition of biopharmaceutics?
Study of the physical and chemical properties of drugs, their route of administration, and how these affect the rate and extent of absorption
what is the result of first pass metabolism?
• Reduction in the amount of drug enteringvthe systemic circulation
• Oral dose needs to be higher when a drugvundergoes extensive first-pass metabolism
• This effect limits bioavailabilit
where do all the veins leaving the GI tract which carry blood rich in nutrients and drug drain to?
hepatic portal vein, taking drug compounds to the liver where they undergo 1st pass metabolism
are acidic drugs ionised at low or high pH
High pH
outline the mechanism for dissolution controlled release system.
• The drug is covered with a slowly dissolving coating
• The liquid surrounding the unit dissolves the coating
• Rate-limiting dissolution step
• Solid drug is exposed to the liquid and dissolves
outline the mechanism of diffusion controlled release systems. (matrix system)
• Drug is dispersed as solid particles within a matrix formed of a water-insoluble polymer (e.g., poly(vinyl chloride)
or in a matrix forming a gel in contact with water
• Release from a matrix system involves:
1. Drug particles located at the surface will be dissolved and released rapidly
2. Drug particles at increasing distances from the surface will be dissolved and released by diffusion in liquid-
filled pores of the matrix or in the gel to the exterior of the release unit
outline the mechanism of diffusion controlled release systems. (Resivoir system)
Release of drug from a reservoir system involves:
- Partition of the drug dissolved inside the release unit to the solid membrane
- Transport by diffusion of the drug within the membrane
- Drug will partition to the solution surrounding the release unit
outline the paracellular route by tight junctions.
Absorption through the gap between neighbouring cells –
tight junctio
outline transcellular route by active transport.
- Molecule “piggybacks” into the cell using a system designed for natural substrates e.g. amino acids, vitamins
- Molecules are moving against a concentration gradient
- Therefore this process requires energy
outline transcellular route by facilitated diffusion.
• A form of passive transport
• No energy is required
• Uses carrier proteins
• Requires a concentration gradient
• Structurally selective
• Competition of different drugs for binding sites
• Saturation on apical side if not enough carrier
