solubility: solvents, co-solvents + salts Flashcards
How can the solubility of a drug be manipulated?
1) selecting correct solvent (use of cosolvents)
2) formation of salt
3) addition of solubilising groups to structure
4) using effect of pH
5) using special dosage forms
aqueous media
polar
lipid based (hydrophobic) media
non-polar
Give some examples of aqueous media.
1) GI tract fluid
2) blood
3) aqueous suspension
4) solution formulations
Give some examples of lipid based media.
1) cell membranes
2) micelles
Give some examples of co-solvents.
1) glycerol
2) propylene glycol
3) ethylalcohol
4) polyoxyethylene
5) glycols
How can co-solvents act?
A) binding to surface of drug
B) inducing preferential hydration
salt
neutral compound comprising positive + negative ions, neither of which is H⁺/OH⁻
Why does the formation of a salt usually improve water solubility of acidic/basic drugs?
salts dissociate in water to form hydrated ions
How is aqueous solubility enhanced?
formation of two charged species
What is the most used counterion for acidic groups?
Na⁻
What is the most used counterion for alkaline groups?
Cl⁻
Why obtain a salt form of a drug?
allows modification of physicochemical characteristics without modifying chemical structure
What do you need to know before selecting a salt form of a drug?
1) molecular structure
2) purity
3) state of hydration or solvation
4) pKₐ
5) logP
