title: Ion-Responsive Drug Delivery Systems.
abstract: Some kinds of cations and anions are contained in body fluids such as blood, interstitial fluid, gastrointestinal juice, and tears at relatively high concentration. Ionresponsive drug delivery is available to design the unique dosage formulations which provide optimized drug therapy with effective, safe and convenient dosing of drugs.
  
  
  
  The objective of the present review was to collect, summarize, and categorize recent research findings on ion-responsive drug delivery systems.
  
  
  
  Ions in body fluid/formulations caused structural changes of polymers/molecules contained in the formulations, allow formulations exhibit functions. The polymers/molecules responding to ions were ion-exchange resins/fibers, anionic or cationic polymers, polymers exhibiting transition at lower critical solution temperature, self-assemble supramolecular systems, peptides, and metalorganic frameworks. The functions of ion-responsive drug delivery systems were categorized to controlled drug release, site-specific drug release, in situ gelation, prolonged retention at the target sites, and enhancement of drug permeation. Administration of the formulations via oral, ophthalmic, transdermal, and nasal routes has showed significant advantages in the recent literatures.
  
  
  
  Many kinds of drug delivery systems responding to ions have been reported recently for several administration routes. Improvement and advancement of these systems can maximize drugs potential and contribute to patients in the world.
authors.affiliation: Evolving Medical Solutions, Astellas Pharma Inc., Tsukuba, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Yoshida
authors.affiliation: Evolving Medical Solutions, Astellas Pharma Inc., Tsukuba, Japan.
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Shakushiro
authors.affiliation: Astellas Ireland Co., Limited, Dublin, Ireland.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sako
mesh_terms: D001826:Body Fluids / Q000737:chemistry*; D003692:Delayed-Action Preparations; D004339:Drug Compounding / Q000379:methods*; D016503:Drug Delivery Systems; D006801:Humans; D007477:Ions; D011108:Polymers / Q000737:chemistry*
chemical_list: D003692:Delayed-Action Preparations; D007477:Ions; D011108:Polymers
keywords: Ion-responsive drug delivery system; controlled drug
  release; in situ gelation; ion-exchange complex; lower critical solution temperature; ophthalmic prolonged retention; salting-out effect; taste-masking