1. Dr. Prashant L. Pingale
GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education and Research,
Significance of Tonicity
2. Learning outcomes
On successful completion of this unit learners shall able to:
Explain in-detailed about significance of tonicity adjustment.
3. Isotonic or Iso–osmotic solutions
A solution containing 0.9% of sodium chloride is practically isotonic with blood plasma
and is regarded as standard.
A solution containing more than 0.9% sodium chloride is called ‘hypertonic’.
A solution containing less than 0.9% sodium chloride is called ‘hypotonic’.
Two solutions of different substances having same osmotic pressure at same
temperature are called isotonic solutions.
When isotonic solutions are separated by Semipermeable membrane, no osmosis takes
place. Isotonic solutions have equal molar concentrations.
4. Isotonic solutions
An isotonic solution is when two solutions, separated by a semipermeable membrane, have
equal concentrations of solutes and water.
5. Hypertonic Solution
A hypertonic solution is a solution that contains more solute than the cell which is placed in it.
If a cell with a NaCl concentration of 0.9% is placed in a solution of water with a 10% concentration
of NaCl, the solution is said to be hypertonic.
Hyper means more, meaning that the solution that the cell is placed in contains more solute than the
solution inside of the cell.
When the solution contains more solute, this means that it contains less water.
The solution outside of the cell is 10% NaCl, which means that it is 90% water. The solution inside of
the cell is 0.9% NaCl, which means it is 99.1% water.
Solution flows from a higher concentration of water to a lower concentration of water, as to achieve
Being that the outside solution is 90% water while the inside contains 99.1% water, water flows
from the inside of the cell to the outside solution to dilute the high areas of solute concentration,
results in loss of water from cell and cell shrinks.
6. Hypotonic Solution
A hypotonic solution is a solution that contains less solute than the cell which is placed in it.
If a cell with a NaCl concentration is placed in a solution of distilled water, which is pure
water with no dissolved substances it, the solution on the outside of the cell is 100% water
and 0% NaCl. Inside of the cell, the solution is 99.1% water and 0.9% NaCl.
Water, again, goes from a higher concentration to a lower concentration.
So water goes from the distilled water solution to the inside of the cell.
As a consequence, the cell swells up and possibly bursts.
Thus, putting a cell with solute in a distilled water solution will cause swelling and possible
bursting of the cell.
7. Tonicity adjusting agents
Tonicity Agents are used in many parenteral and ophthalmic products
to adjust the tonicity of the solution.
The goal for every injectable product to be isotonic with physiologic
fluids, this is not an essential requirement for small volume injectables
The products administered by all other routes, especially into the eye
or spinal fluid, must be isotonic.
Injections into the subcutaneous tissue and muscles should also be
isotonic to minimize pain and tissue irritation.
The agents most commonly used are electrolytes and mono- or
Some solutions are iso-osmotic but not isotonic. This is because the
cell membrane of the red blood cell is not semipermeable to all drugs.
8. Why only 0.9%w/v of NaCl is
isotonic with blood serum?
The statement that 0.9%w/v NaCl is isotonic is incomplete. The fact that it is isotonic with
This means they have the same osmotic pressure as each other which controls how they
pass through the semi permeable membrane of blood vessels.
0.9%w/v NaCl is isotonic with blood serum and that means that it will diffuse out of the
blood vessel after IV injection in a similar fashion to the components of the blood serum
0.9%w/v NaCl contains about 154 mOsm/L of Na+ and 154 mOsm/L of Cl- giving the
solution an osmolarity of 308 mOsm/L.
The osmolarity of blood is about 300-310 mOsm/L so the two are very close and that's why
0.9%w/v NaCl is considered isotonic for IV solution.
9. How this 154 does appears?
The molecular weight of sodium chloride is approximately 58.5 grams per mole, so
58.5 grams of sodium chloride equals 1 mole.
Normal saline contains 9 grams of NaCl, the concentration is 9 grams per liter divided
by 58.5 grams per mole, or 0.154 mole per liter.
As NaCl dissociates into two ions – sodium and chloride – 1 molar NaCl is 2 osmolar.
Thus, NS contains 154 mEq/L of Na+ and Cl-
One litre of 0.9% Saline contains:
154 mEq of sodium ion = 154 mmol/L
154 mEq of chloride ion = 154 mmol/L