[Anything] HCl: Why is hydrochloric acid such a common solvent in drug formulas?

I have a lot of occasion to look at the promotional junk drug companies give out, which is always emblazoned with the name and active ingredient of a specific drug. For example, I have a pen in my hand that hypes Zofran, which is ondansetron HCl and an injectable. I also have a Zoloft magnet (“The Zoloft Smile,” which itself sounds like a disease :D), and Zoloft is sertraline HCl.

I can dig up more examples, but those in the know have probably already noticed.

So, why is hydrocholric acid such a common solvent in these drug formulations? I only have high school chemistry, but I can pick things up pretty quick.

The HCl is used to form the salt of the amine (base), which is a functional group in the drug.

The salt is a stable form of the drug, slowing down the loss of the product over time and making it more easy to handle.

You may notice that there are other acids used to form the salt of different types of drugs. Some of these, eg the succinate are organic.

btw, dont think of the HCl as a solvent. It is quite the opposite.

Why HCl… because it less likely to react with the compound, is stable, has fairly low contribution of the overall molecular mass and is cheap.

further to what antechinus said, most amines are not very water soluble. But the HCl salt is because it is charged, hence dissolves in the water solvent used to inject

BTW in drugs is HCl Hydroclroide, not hydrochloric acid like in the title.

The reason the formulas are written and referred to this way is to highlight the parent amine.

A very simple example is the compound ammonium chloride (NH[sub]4[/sub]Cl).

One could also refer to this compound as “ammonia hydrochloride,” which could be written as NH[sub]3[/sub]HCl.

Drugs generally involve far more complex parent amines. BTW, these “hydrochloride compounds” are known as acid salts. These particular salts are useful due to their solubility in water, which makes it easy to get to get the drug into your system when taken orally.

One last point, the cation in these acid salts are weak acids (such as ammonium ion in my example above). There is no actual hydrochloric acid present in the salt.