Significance of tonicity adjustment

Significance of tonicity adjustment

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  Dr. Prashant L.Pingale Associate Professor-Pharmaceutics GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education and Research, Nashik Significance of Tonicity Adjustment
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  Learning outcomes  Onsuccessful completion of this unit learners shall able to:  Explain in-detailed about significance of tonicity adjustment. 2
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  Isotonic or Iso–osmoticsolutions  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. 3
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  Isotonic solutions  Anisotonic solution is when two solutions, separated by a semipermeable membrane, have equal concentrations of solutes and water. 4
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  Hypertonic Solution  Ahypertonic 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 equilibrium.  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. 5
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  Hypotonic Solution  Ahypotonic 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. 6
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  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 administered intravenously.  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 disaccharides.  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. 7
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  Why only 0.9%w/vof 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 blood serum.  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 itself.  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. 8
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  How this 154does 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 9
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  Why using isotonicsolutions10
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  Methods to adjustthe tonicity11 Tonicity Methods NaCl Equivalent Method White- Vincent Methods Molecular Concentration Method Cryscopic Method