oral dosage forms Flashcards
why is dissolution rate of weak acids low in the stomach
because the drug is in its unionised form
how can you increase the ph of the diffusion layer
forming an alkaline salt of the weak acid
sodium and potassium ions release OH ions which promote ionisation
state of ionisation solubility and permeability of weak bases in gastric environment
ionised, high sol, low per
state of ionisation solubility and permeability of weak bases in the intestine
unionised, low sol, high(er) per
state of ionisation, sol and per of a weak acid in a gastric environment
unionised, low sol high per
state of ionisation, sol and per of a weak acid in the intestine
ionised, high sol and low per
what effect does the presence of food have on the pH and why
lowers ph due to slower emptying time and acid being released
what does a low log D value conclude
the low surface area of the stomach
3 effects of solubility issues
low BA
incomplete release of drug from dosage form
high inter patient variability
what does a negative log P value suggest
hydrophillic
what does a positive log P value suggest
lipophilic
range for good solubility
0.1-10mg/ml
4 ways to improve solubility
cyclodextrins
polar excipients
sugar glasses
SCFs
explain how cyclodextrins improve solubility and their side effects
hydrophobic interior
hyrophillic exterior
form complexes with hydrophobic compounds
hydrophilic polymers can also increase the solubilising effect of cyclodextrins
se= toxic and unstable
how do polar excipients improve solubility & example
e.g. gelatin - positive and negative charges improve the gettability of hydrophobic drugs
