[Venoxis]

Hello dear chem community :-)

I noticed that most pharmaceuticals are offered as HCl and in some rare cases as HBr or even as tartrates. Considering they are all water soluble I do wonder where the choice for different types of salts comes from. If it is for purely economical reasons, wouldn't it make more sense to convert all basic APIs into tartrate salt? That would be the cheapest option. Or do different salts have varying degrees of solubility? I noticed for example that morphine used to be offered as a tartrate back in the early to mid 20th century but now it's only as an HCl salt.

So does the choice in salt type really matter or is it purely an economical decision?

[rolnor]

you want nice pure crystals when you purifiy by recrystalization at the end of the synthesis Some salts does this better than others. Also how sensitive the salt is to moisture, it should be stable.

[Babcock_Hall]

Sometimes tartrate is used to separate enantiomers.

[Venoxis]

Sometimes tartrate is used to separate enantiomers.

That's interesting. Never thought this was possible. Thanks!

[rolnor]

Sometimes tartrate is used to separate enantiomers.

I think this was more common earlier, today we have enantioselektive synthesis methods in most cases. You have to throw away half your product yield if you separate the racemic mixture

[Venoxis]

Another question just popped into my mind: if different salts have different solubility profiles, doesn't that mean in regards to APIs that the same compound has to be dosed differently depending on which salt is being used? Diphenhydramine for example has four known salts: hydrochloride, methyl bromide, salicylate and citrate. Let's suppose DPH is most acidic (in other words most water soluble) as a hydrochloride, and most basic (in other words most lipophilic and therefore least water soluble) as a methyl bromide. Wouldn't that mean DPH as a methyl bromide would need to be dosed higher than the same drug as a hydrochloride since its resorption capacity is the worst due to its lipophilicity?

[Babcock_Hall]

I am a little confused; methyl bromide is an alkylating agent, not an acid.

[rolnor]

Any salt of an amine will form cations in the stomach acid and chloride will be the dominating anion.

[Hunter2]

I am a little confused; methyl bromide is an alkylating agent, not an acid.

Tetraalkyl(Aryl) ammonium cathions are existing. Made from an Trialkyl(Aryl)amin and an Alkyl(Aryl)halogenid.

Means additional to HX also RX can be used.

[Babcock_Hall]

If one alkylates the amine group, the drug will be permanently changed.