Isotonic solutions in pharmaceutical preparations.

 Certain pharmaceutical solutions should have controlled tonicity. Especially if they are intended for administration on delicate tissues such as the eye, nasal cavity, or blood circulation. Tonicity expresses osmetic pressure of solutions. When two solutions have the same osmetic pressure they are referred to as isoosmetic. However, if they are separated by a semipermeable membrane (allows passage of water molecules only) then they are referred to as isotonic.  Accordingly, solutions can be classified as hypotonic, isotonic, or hypertonic  relative to osmotic pressure of biological fluids. Sodium chloride solution of 0.9 % (w/v) also known as normal saline is an isotonic solution. When such a solution is administered to biological membranes or fluids it does not cause irritation or discomfort. However, hypotinc and hypertonic solutions can cause irritation or discomfort when added to biological fluids or membranes. Biological cells in contact with hypotonic solutions swell and might burst due to excess passage of water into them. On the other hand, cells in contact with hypertonic solutions shrink due to passage of water towards the solution with a higher osmetic pressure.

Examples on isotonic solutions:
0.9 % (w/v) sodium chloride.
5.6 % (w/v) dextrose monohydrate.
2.7 % (w/v) glycerin.
11.3 % (w/v) sucrose.
1.2 % (w/v) potassium chloride.
12.9 % (w/v) lactose.

Note: %w/v is a concentration expression for weight of solute (g) in 100 ml solution.
Note: Solutions intended for use on delicate tissues should also have an optimized pH value to avoid tissue irritation.

Related posts:
Examples on calculations for pharmaceutical isotonic solutions.
How to prepare isotonic solutions.