Why do most prescription medications end in HCl? Is hydrochloric acid added to prescription drugs for some reason? Does it stand for something else entirely?
There are quite a few medications that contain hydrochlorides, rather than hydrochloric acid.
I’ve heard that some commonly prescribed drugs come in both sulfate and HCL versions; the HCl can be an alternative for those allergic to sulfates.
Many drugs contain both acidic (eg carboxyl) and basic (eg amine) groups as part of their structure. HCl is added in order to neutralize these groups and control the pH of the dried product. It acts by forming salts with the acidic and basic groups, hence the term “HCl salt.”
Sometimes, the hydrochloride is the water-soluble version of the drug. One example that comes to mind is ampicillin (a penicillin variant). “Free” ampicillin is insoluble in water. The hydrochloride is water soluble.
And sometimes the water-soluble version is not suitable for the particular dosage form, so the hydrochloride is not used. For instance, people snort cocaine hydrochloride, but they smoke cocaine in its “free base” form – hence “freebasing.”
Is the HCl used for pHing? Many solutions are written this way (Tris-Acetate, Tris-HCl) but I’m not sure if there is a relation.
“Is the HCl used for pHing?”
Sometimes. As Dogface and Nametag pointed out, there are also other reasons that HCl is used. I just picked the simplest example. Tris-HCl is Tris base that’s been titrated to a specific pH, usually around 8, with hydrochloric acid.
I’ve also seen hydrobromide (HBr) formulations, such as dextromethorphan hydrobromide, often found in cold medicines.
it is used when the drug contains an amine. Large amines are not normally water soluble, but adding an acid (e.g. HCl) will form a salt with it and make it soluble.
The opposite problem comes if you want to smoke an amine - free base (no HCl) is volatile - HCl salt not.