Which term describes a drug that is paired with another to form a more soluble compound?

• A. Co-crystals
• B. Salt forms
• C. Hydrates
• D. Amorphous solids

Answer: (B)

Salt formation increases solubility by converting a drug into an ionic form through pairing with a counterion. When a drug that is a weak acid or base forms a salt, it becomes charged, and the resulting salt readily dissociates in water. This ionization lowers lattice energy and enhances interactions with water molecules, leading to better dissolution and often improved bioavailability. This is the common approach used to make poorly soluble drugs dissolve more readily in the stomach and intestines. Co-crystals can also improve solubility, but they rely on non-ionic interactions with a separate co-former rather than converting the drug into an ionic salt. Hydrates involve water in the crystal lattice, which can affect solubility in various ways, and amorphous solids may dissolve faster but are typically less stable. Therefore, the term that describes a drug paired with another to form a more soluble compound is salt forms.