Pharmaceutics - Excipients for Matrix Tablets Flashcards
In the biopharmaceutical classification systems (BCS), describe the solubility and permeability of class 1 drugs?
high sol and high perm
In the biopharmaceutical classification systems (BCS), describe the solubility and permeability of class 2 drugs?
low sol and high perm
In the biopharmaceutical classification systems (BCS), describe the solubility and permeability of class 3 drugs?
high sol and low perm
In the biopharmaceutical classification systems (BCS), describe the solubility and permeability of class 4 drugs?
low sol and low perm
what factors affect drug bioavailability?
- Drug release: Drug must be released into and dissolve in GI fluids to be absorbed across GI mucosa.
- Drug solubility: Low drug solubility in GI fluids associated with slow drug dissolution and thus absorption.
- GI permeability: Low GI mucosal permeability associated with slow drug diffusion across GI mucosa.
what is a hydrophilic matrix tablet?
- an extended release formulation containing gel-forming polymers
- usually produced by dry granulation or direct compression
How does a hydrophilic matrix tablet work?
- uses a combination of drug diffusion and matrix erosion
- the polymer matrix swell upon hydration, then the tablet gels from outside in.
- This gel forms a diffusion barrier
- the soluble matrix then erodes slowly and the drug diffuses out
Give examples of matrix formers?
- hydroxypropyl cellulose
- Hydroxypropyl methylcellulose
- polyethylene oxide
what factors reduce the rate of release of hydrophilic matrix tablets?
Higher:
- molecular weight
- proportion of polymer content
- degree of hydrophobic substitutions
- degree of polymer cross-linking
what makes polyethylene oxide a more useful hydrophilic matrix?
its higher molecular weight
what is an insoluble matrix tablet?
an extended release formulation containing porous insoluble polymer matrix
how does an insoluble matrix tablet work?
- Diffusion-based system (polymer matrix remains intact).
- Drug incorporated in pores.
- As water enters pores, drug dissolves and diffuses out
through water-filled pores. - First-order drug release.
- Insoluble polymer shell egested.
what is a monolithic tablet?
- a single-unit tablet with an IR core and ER coating.
- Rate of drug release is dependent on the coating
what is a multiple-unit tablet?
- a MR coated pellet in a IR tablet matrix.
- rate of drug release dependent on coating
what are the differences between multiple-unit tablets and single-unit tablets?
- lower risk of dose dumping in multiple-unit than in single-unit tablets
- multiple-unit tends to use pellets rather than tablets due to less susceptibility to gastric entrapment
what are the two ways membrane-controlled ER tablets work?
- Membrane hydrates and swells, opening
diffusion pathways. - Soluble polymer plugs (e.g. plasticiser) in insoluble coating dissolves, opening pores. Water diffuses
in and drug diffuses out through pores in membrane
what is an osmotic pump system?
a semi-permeable outer membrane with an orifice in it (a soluble polymer plug/laser-drilled)
how does an osmotic pump system work?
- Water enters dosage form by osmosis through semi-permeable membrane.
- Increased osmotic pressure forces solubilised or suspended drug out through orifice.
- Optional: Push compartment swells, pushing drug out
through orifice. - Zero- or first-order release
what is a gastro-retentive system?
-when the ER formulation evades (avoids) the gastric emptying so drug is retained in the stomach either for treating gastric conditions or due to poor intestinal absorption
How does the gastro-retentive system work?
-if the drug has a high density-it sinks to pyloric region
-if the drug is effervescent then the system generates and entraps CO2, causing
dosage form to float in gastric fluid
-if the drug is magnetic, then it’s retained with an external magnet
-if the drug swells, it enlarges upon hydration so becomes too large to pass through the pylorus
-if the drug is mucoadhesive, it adheres to the gastric lining
