Isotonic solutions have the same osmotic pressure as body fluids like blood. Osmotic pressure depends on the number of particles in solution, including ions from electrolyte dissociation. Solutions with lower osmotic pressure than body fluids are hypotonic, while those with higher pressure are hypertonic. Physiological fluids have an osmotic pressure matching a 0.9% sodium chloride solution, which is therefore considered isotonic. Common isotonic solutions include saline and ringer's solution.

1. ISOTONIC SOLUTIONS
When a solvent passes through a semipermeable membrane from a dilute solution into a more
concentrated one, with the result that the concentrations become equalized, the phenomenon is
known as osmosis.
The pressure responsible for this phenomenon is called osmotic pressure, and it proves to be
caused by and to vary with the solute.
If the solute is a nonelectrolyte, its solution will contain only molecules, and the osmotic
pressure of the solution of the solution will vary only with the concentration of the solute.
If the solute is an electrolyte , its solution will contain ions, and the osmotic pressure of the
solution will vary not only with the concentration, but also with the degree of dissociation of the
solute. Therefore, substances that dissociate have a relatively greater number of particles in
solution and should exert a greater osmotic pressure than could undissociated molecules.
Like osmotic pressure, the other colligative properties of solutions, namely, vapor pressure,
boiling point, and frezzing point, depend on the number of particles in solution.
These properties, therefore, are related, and a change in any one of them will be attended by
corresponding changes in the others.
Two solutions that have the same osmotic pressure are termed isosmotic.
Many solutions intended to be mixed with body fluids are designed to have the same osmotic
pressure for greater comfort, efficacy, and safety.
A solution having the same osmotic pressure as a specific body fluid is said to be isotonic
(meaning of equal tone) with that body fluid.
Solutions of lower osmotic pressure than that of a body fluid are hypotonic, whereas those
having a higher osmotic pressure are hypertonic.
Isotonic solution:
Example;
 0.9% sodium chloride solution
 5% glucose
 Ringer's solution
 Lactated ringer's solution

2. Isotonic Solutions:
When two solutions have same osmotic pressure and salt concentration are said to be ''isotonic
solution".
iso (same) and tonic (concentration).
Physiologically, isotonic solutions are solutions are solutions having the same osmotic pressure
as that of the body fluids when separated by a biological membrane. Biological fluids including
blood and lachrymal fluid normally have an osmotic pressure corresponding to that of 0.9% w/v
solution of sodium chloride. Thus 0.9% solution of sodium chloride is said to be isotonic with
the physiological fluids.
Isotonic solution is a solution having the same osmotic pressure on a body fluid, ophthalmic
(eye), nasal (nose), and parenteral (injection) solution should be isotonic.
Buffered isotonic solutions:
Isotonic solution: Solutions containing the same concentration of particles and thus exerting
equal osmotic pressure are called iso-osmotic.
A 0.9% solution of Nacl(normal saline) is iso-osmotic with blood and tears. The term iso-tonic,
meaning equal tone, is sometimes used interchangeably with the term iso-osmotic.

3. Hypotonic solution: solution which contain fewer particles and exert a lower osmotic pressure than 0.9%
saline are called hypotonic.
Administration of a hypotonic solution produces painful swelling of tissues as water passes from the
administration site into the tissues or blood cells.
Hypertonic solution s: those solutions exerting higher osmotic pressures are referred to as hypertonic.
Hypertonic solutions produce shrinking of tissues as water is pulled from the biological cells in an
attempt to dilute the hypertonic solution.
Tonicity is a measure of the effective osmotic pressure gradient, as defined by the water
potential of two solutions separated by a semipermeable membrane. In other words, tonicity is
the relative concentration of solutes dissolved in solution which determine the direction and
extent of diffusion. It is commonly used when describing the response of cells immersed in an
external solution.
Unlike osmotic pressure, tonicity is influenced only by solutes that cannot cross the membrane,
as only these exert an effective osmotic pressure. Solutes able to freely cross the membrane do
not affect tonicity because they will always be in equal concentrations on both sides of the
membrane. It is also a factor affecting imbibition.

4. References
1. Mitchell J. Stoklosa,Howard C. Ansel (1996). Pharmaceutical calculations Source Book:
isotonic solutions. p. 144.ISBN 81-7431-023-1
2. https://en.wikipedia.org/wiki/Tonicity
3. https://www.google.com