Provided herein are highly water soluble, thiazolidinone derivative compounds and glycine hydrazide derivative compounds that inhibit the ion transport activity of the cystic fibrosis transmembrane conductance regulator (CFTR). The compounds, and compositions comprising the compounds, described herein are useful for treating diseases, disorders, and sequelae of diseases, disorders, and conditions that are associated with aberrantly increased CFTR activity, for example, secretory diarrhea. The compounds may also be used for inhibiting expansion or preventing formation of cysts in persons who have polycystic kidney disease.
