Is there any difference between isotonic and isosmotic solution? Can we say isotonic solution do not show osmosis because they have same osmotic pressure?

  • $\begingroup$ I think often you can use those terms interchangeably but they aquire different meanings in some contexts. According to the current entry in the wikipedia, an isotonic solution does not alter the solvent concentration in a second solution, the standard example being the interior of a red blood cell. In contrast an iso-osmotic solution may do so. $\endgroup$ – Buck Thorn Jan 30 '19 at 19:18

Yes, there is a difference. Isotonicity implies a biological compatibility, whereas isoosmoticity implies similarity of chemical and/or physical composition. Solutions that are isoosmotic to biological fluids/blood are not necessarily isotonic as tonicity refers to a given cell membrane [1, p. 230]:

The 0.9% sodium chloride solution is said to be iso-osmotic with physiological fluids. In medicine, the term isotonic, meaning equal tone, is commonly used interchangeably with iso-osmotic. However, terms such as isotonic and tonicity should be used only with reference to a physiological fluid. Iso-osmotic actually is a physical term that compares the osmotic pressure (or another colligative property, such as freezing-point depression) of two liquids, neither of which may be a physiological fluid, or which may be a physiological fluid only under certain circumstances. For example, a solution of boric acid that is iso-osmotic with both blood and lacrimal fluid is isotonic only with the lacrimal fluid. This solution causes hemolysis of red blood cells because molecules of boric acid pass freely through the erythrocyte membrane regardless of concentration. Thus, isotonicity infers a sense of physiological compatibility where iso-osmoticity need not. As another example, a chemically defined elemental diet or enteral nutritional fluid can be iso-osmotic with the contents of the GI tract, but would not be considered a physiological fluid, or suitable for parenteral use.


  1. Gennaro, A. R. Remington: The Science And Practice Of Pharmacy, 21st ed.; Lippincott Williams & Wilkins: Philadelphia, 2005. ISBN 978-0-7817-6378-3.

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