The Chloride Ion (DB14547): A Comprehensive Monograph on its Physicochemical Properties, Physiological Functions, and Clinical Significance

Section 1: Introduction: Beyond a Simple Molecule

The chloride ion (Cl−), cataloged in the DrugBank database as DB14547, represents a unique entry in the pharmacological compendium.[1] Unlike conventional therapeutic agents, which are typically xenobiotic compounds designed to elicit a specific biological response, chloride is the most abundant extracellular anion in the human body, a fundamental electrolyte indispensable for life.[3] Its classification as an investigational "Small Molecule" within such a database stems not from a primary pharmacological activity in the traditional sense, but from its ubiquitous presence in a vast array of therapeutic formulations, where it serves as a counter-ion, an essential component of intravenous hydration solutions, or as part of an active pharmaceutical ingredient.[1]

The presence of chloride ion in listings for clinical trials for conditions ranging from urinary tract infections to various cancers can be misleading.[7] A detailed examination reveals that in these contexts, chloride is not the substance under investigation. Instead, it is a constituent of the therapeutic regimen—for example, as the counter-ion in chlorhexidine, a ligand in the cisplatin molecule, or the principal anion in the 0.9% sodium chloride (saline) solution used as a vehicle for drug delivery or for patient hydration.[7] This distinction is critical: chloride's