D2 Medicines: physiological properties 2 Flashcards
What sort of solvent have a high relative permittivity?
polar solvents
How do polar solvents dissolve ionic solutes?
by reducing the force of attraction between oppositely charged ions in crystalline solids
How do polar molecules solvate molecules and ions?
through dipole-dipole forces
Ranitidine free base has a low aqueous solubility, how can we ensure ranitidine gets absorbed?
ranitidine free base has a low aqueous solubility, unstable to light and has a sulphurous odour. reacting with a strong acid (HCl) produces the salt ranitidine HCl - which is odourless, stable, has a greater aqueous solubility. ranitidine HCl will ionise hence has a greater solubility.
What can semi-polar solvents dissolve and give examples of them?
Polar and non polar substances
acetone, methanol, ethanol, other alcohols
What prevents Non polar solvents dissolving ionic or polar solutes? Give examples
h-bonding
hexane
pentane
oils and fats
What influences the solubility of weak acids and bases?
pH
Give examples of weakly acidic drugs
phenobarbital, phenytoin, warfarin, NSAIDs
What is the Henderson- Hasselbalch?
pKa= pH+ log[HA]/[A-}
What equation can tell us the pH at which a drug will start to precipitate?
pH= pKa+ log (S-So)/So
What does S =?
saturation, solubility of weakly acidic drug at a given pH
What does So=?
solubility of undissociated drug
Give examples of weakly basic drugs
Ranitidine, cimetidine
What is the HH equation for a weak base?
pKa= pH + log[BH+]/[B]
What is the solubility equation for a basic drug?
pH= pKa+ log So/(S-So)
