Lowosmolar

Low-osmolar, or lowosmolar, is a term used in medicine to describe solutions or contrast agents whose osmolarity is lower than that of older high-osmolar formulations. Osmolality measures solute concentration per kilogram of solvent, and comparisons are often made to plasma osmolality, roughly 290 mOsm/kg. In radiology, low-osmolar contrast media (LOCMs) are iodinated agents with osmolality substantially lower than traditional high-osmolar contrast media, typically in the range of about 600–850 mOsm/kg. Many LOCMs are nonionic, meaning they do not dissociate into charged particles in solution, a feature associated with a lower rate of certain adverse reactions compared with ionic, high-osmolar agents. A separate class, iso-osmolar contrast media (IOCM), such as iodixanol, has osmolality similar to plasma (~290 mOsm/kg).

Clinical impact of LOCMs includes a generally lower incidence of adverse reactions and improved tolerability, particularly in patients at higher risk for contrast-related complications, such as those with kidney impairment. Nevertheless, the risk of nephrotoxicity and hypersensitivity is not eliminated, so patient factors—renal function, hydration status, concomitant nephrotoxic medications—inform agent choice. LOCMs are widely used in radiologic procedures, including computed tomography and angiography, where injection rate and viscosity influence imaging quality and workflow. Costs are typically higher than older high-osmolar agents, which can affect selection in some settings. Ongoing guidelines emphasize individualized assessment and hydration as part of safe contrast administration.