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Is there a reason for why most medicines are in salt form?

Why not have them in conjugate base form?

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In general, salts are more soluble in water than organic acids or organic bases, because they are made of ions. It is a general trend. There are plenty of exceptions. So usually salts are quickly dissolved in the stomach and absorbed in the intestine later on.

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  • $\begingroup$ thank you for your answer, but how does this work? they dissociate to the ions anyway, so does the conjugate base alone not dissociate @maurice ? $\endgroup$
    – Nickotine
    Mar 27, 2021 at 10:24
  • $\begingroup$ An organic base is a molecule made of covalent bonds. It will not dissociate. A good example is ammonia $\ce{NH3}$ (which is not organic) and amines obtained by replacing one H by $\ce{CH3}$ or $\ce{C2H5}$ or any other organic radical- These molecules are not polar, they cannot dissociate, and are not too much soluble in water. And all they can do is to accept a proton from an acid. In that case it becomes charged and soluble into water. $\endgroup$
    – Maurice
    Mar 27, 2021 at 21:29
  • $\begingroup$ thank you very much now I get it @maurice $\endgroup$
    – Nickotine
    Mar 27, 2021 at 22:52
  • $\begingroup$ actually I have another question if it’s a hcl salt for example it’s only the h and cl that ionise, the substance still exists in its pure form not an ion... perhaps it’s just a cost thing? @maurice $\endgroup$
    – Nickotine
    Mar 28, 2021 at 17:20
  • $\begingroup$ i think this only applies to sodium salts not hx salts @maurice $\endgroup$
    – Nickotine
    Mar 28, 2021 at 17:29
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Indeed, 50% of the US’s FDA approvals consists of compounds in the salt form, (Paulekuhn et al. 2007) but the choice depends on multiple factors beyond the acid/salt choice as Gupta et al. (2018) noted in their review:

The physicochemical and biological properties of active pharmaceutical ingredients (APIs) are greatly affected by their salt forms. The choice of a particular salt formulation is based on numerous factors such as API chemistry, intended dosage form, pharmacokinetics, and pharmacodynamics. The appropriate salt can improve the overall therapeutic and pharmaceutical effects of an API. However, the incorrect salt form can have the opposite effect, and can be quite detrimental for overall drug development.


References

Paulekuhn, G.S., Dressman, J.B., and Saal, C. (2007) “Trends in active pharmaceutical ingredient salt selection based on analysis of the orange book database.” J. Med. Chem. 50:6665. DOI: 10.1021/jm701032y

Gupta, D., Bhatia, D., Dave, V., Sutariya, V. and Gupta, S.V. (2018) “Salts of Therapeutic Agents: Chemical, Physicochemical, and Biological Considerations.” Molecules 23:1719. DOI: 10.3390/molecules23071719

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  • $\begingroup$ @z1237 please see my comment to maurice’s answer, I’m trying to understand how it works $\endgroup$
    – Nickotine
    Mar 27, 2021 at 10:25

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