Introduction:

Chloride ions are the predominant anionic counter-ion present in vivo (intestine/ jejunum: 0.13M and stomach: 0.10M), significantly effecting solubility and dissolution of drugs for oral absorption1. Our group has recently discovered a novel small molecule, with good permeability but low aqueous solubility potentially limiting exposure after oral administration. It is a basic compound (pKa- 6-7) and provides opportunities to develop salt exploiting different counter-ions. Solubility is not only dependent on the ionization of the weak acid or weak base itself but also on the solubility of the counter ion pairs. Counter ion exchanges between salt forms or formation of hydrates is well known to occur in the gastrointestinal environment. If this happens, then formation of less soluble species can lead to in vivo precipitation of the drug.