Two solutions having the same osmotic pressure across a semipermeable membrane is referred to as an isotonic solution. It has the same osmolarity (solute concentration), as another solution. A solution is isotonic when its effective osmole concentration is the same as that of another solution. This state provides the free movement of water across the membrane without changing the concentration of solutes on either side. Some examples of isotonic solutions are 0.9% normal saline and lactated ringers.
