Isotonic solutions – Pharmaceutics – I B. Pharma 1st Semester

Isotonic solutions

Isotonic-solutions

Objective

At the end of this lecture, student will be able to

• Explain osmosis phenomenon

• Predict the effect of paratonic solutions on blood cells

• Calculate quantities for preparation of isotonic solutions by various methods

Introduction

• Osmosis – movement of solvent molecules from Lower concentration to higher concentration until equilibrium is established

• Pressure driving this movement – Osmotic pressure

• Osmotic pressure is driven by

– Number of particles of solute in solution

– Nonelectrolytes – Solute concentration

– Electrolytes – Solute conc and degree of dissociation

• Solutions with same conc of particles- solutions exerting same osmotic pressure

Isotonic or equal tone – solution which is iso-osmotic with blood and tears

• Normal saline – 0.9% solution of NaCl Isotonic

Hypotonic – lower osmotic pressure than body fluids

Hypertonic – Higher osmotic pressure than body fluids

Effect of paratonic (hypertonic/hypotonic) solutions on RBC

What Are Isotonic Solutions?

Isotonic solutions are solutions with the same osmotic pressure as bodily fluids like blood or tears. These solutions are formulated to match the body’s natural salinity, making them ideal for various medical applications. They neither draw water into the cells (hypotonic) nor pull water out of the cells (hypertonic).

How Do Isotonic Solutions Work?

Isotonic solutions work by preventing a net movement of water into or out of the cells. This ensures that cells neither swell nor shrink, maintaining their normal size and function. This balance is critical for various bodily functions, from cellular hydration to normal tissue function.

Benefits of Isotonic Solutions

  • Cellular Hydration: Isotonic solutions keep cells hydrated without causing them to burst or shrink.
  • Medication Delivery: They are used as a medium for administering medications intravenously.
  • Fluid Replacement: Ideal for rehydrating patients and athletes after strenuous activities.
  • Ophthalmology: Isotonic solutions are used to rinse the eyes and contact lenses.

Common Uses of Isotonic Solutions

Isotonic solutions find applications in a wide range of medical and non-medical scenarios:

  • Intravenous (IV) Drips: Used in hospitals to provide fluids and electrolytes to patients.
  • Eye Care: Used as eye drops or for contact lens cleaning.
  • Wound Irrigation: Effective for cleaning wounds and preventing infection.
  • Sports and Fitness: Popular among athletes for rehydration after intense workouts.

Types of Isotonic Solutions

The most common isotonic solution is Normal Saline (0.9% Sodium Chloride), but there are other types with specific medical uses, such as Lactated Ringer’s solution and Dextrose 5% in Water.

Hypertonic vs. Hypotonic vs. Isotonic Solutions

Understanding the differences between hypertonic, hypotonic, and isotonic solutions is crucial for their proper application. Hypertonic solutions have a higher solute concentration than bodily fluids, causing cells to shrink, while hypotonic solutions have a lower solute concentration, causing cells to swell.

Freezing point depression method

• The freezing point of body fluids is -0.52⁰C

• Dissolved substances in body fluids (plasma and tears) depress the freezing point

• Any solution that has freezing point -52⁰C is isotonic with body fluids

Percentage W/V of adjusting substance needed = 0.52-a/b

a = freezing point of the unadjusted solution

b= freezing point of a 1%w/v solution of the adjusting substance 

Example:

What concentration of procaine hydrochloride will yield a solution iso osmotic with blood plasma?

Freezing point of 1%w/v solution of procaine HCl is 0.122⁰C

%w/v of procaine HCl required = 0.52 – 0/0.122

   = 4.26%w/v

Practice problems

• Find the concentration of sodium chloride required to render a 1% solution of cocaine HCl iso osmotic with blood plasma. Freezing point of 1%w/v solution of cocaine HCl & 1% NaCl is 0.09⁰C and -0.576⁰C resp.

• Find the concentration of NaCl required to render a 1.5% solution of procaine HCl iso osmotic with plasma. Freezing point of 1%w/v solution of procaine HCl & 1% NaCl is -0.122⁰C and -0.576 ⁰C resp.

Molecular concentration method

• At normal temperature and pressure, one gram molecule of a non-ionizing solute in 22.4 litres has an osmotic pressure of one atmosphere.  

• A solution containing one gram molecule in one litre will have an osmotic pressure of 22.4 atmospheres.

• Osmotic pressure of body fluids ≈ 6.7 atm  

• Molarity of body fluids = 6.7/22.4 = 0.3M

I gm mol. wt in 22.4 liters   —- > 1 atm

1 gm mol. Wt in 1 litre        —- > 22.4 atm

22.4 atm —- > 1 gm mol. Wt (1 M)

6.7 atm   —- >  ?

i.e, 6.7 / 22.4 = 0.3 M

Therefore it can be said that, 0.3M solution of any non-ionizing solution will be iso-osmotic with plasma and tears

W = 0.3 M / N

W = Concentration required in grams / litre

M = Mol. wt of the solute

N = No. of ions produced from each molecule of the solute assuming that dissociation is complete

Example: Find the concentration of NaCl required to produce a solution iso-osmotic with blood plasma. Mol. wt of NaCl is 58.5 and it dissociates into 2 ions.

0.3 X 58.5/2 = 8.8 g/Lt or 0.9% w/v

Practice problems

• Find the concentration of dextrose required to make a 0.12% solution of NaCl iso-osmotic with blood plasma.

• Give the formula for 500 ml of an intravenous solution containing 2% of anhydrous dextrose and 0.5% KCl and made iso-osmotic with blood plasma.

Mol. Wt of dextrose = 180; 

Mol. Wt of KCl = 74.5

Mol. Wt of NaCl = 58.5

Sodium chloride equivalent method

• Specified concentration of the medicament converted to concentration of NaCl producing the same osmotic effect

Eg. The freezing point depression produced by 1% w/v ascorbic acid solution is 0.105 ⁰C. Freezing point depression of 1%NaCl solution = 0.576 ⁰C

NaCl equivalent of 1% ascorbic acid = 0.105/0.576 = 0.18

Percentage of NaCl for adjustment to isotonicity is given by

Practice problems

• Calculate the % of NaCl required to render a 0.5% solution of KCl iso-osmotic with blood plasma. NaCl equivalent of 1% KCl solution = 0.76

0.9 – (percentage strength of medicament X NaCl equivalent of 1% medicament)

• Calculate the % of anhydrous dextrose required to render a 1% solution of ephedrine HCl iso osmotic with body fluids. NaCl equivalent of 1% ephedrine HCl solution = 0.3

Summary

• Osmosis – movement of solvent molecules from Lower concentration to Higher concentration – Untill equillibrium is established

• Pressure driving this movement – Osmotic pressure

• Isotonic – same osmotic pressure than body fluids

Hypertonic – higher osmotic pressure than body fluids

Hypotonic solutions– lower osmotic presssure than body fluids

Adjustment of isotonicity by 

Freezing point depression method

Percentage W/V of adjusting substance needed = 0.52-a/b

Molecular concentration method

W = 0.3 M / N

Sodium chloride equivalent method

0.9 – (percentage strength of medicament X NaCl equivalent of 1% medicament)

Frequently Asked Questions

  1. Are isotonic solutions safe for everyone? Isotonic solutions are generally safe, but specific medical conditions may require caution. Consult a healthcare professional for guidance.
  2. Can I make isotonic solutions at home? Isotonic solutions should be prepared under controlled conditions. It’s safer to use commercially available ones.
  3. Are there any alternatives to isotonic solutions? Hypertonic and hypotonic solutions serve different purposes and may not be suitable alternatives.
  4. How do isotonic solutions benefit athletes? Athletes use isotonic solutions to rehydrate and restore lost electrolytes, enhancing their performance and recovery.
  5. Can isotonic solutions be used for pets? Isotonic solutions are sometimes used for rehydration in pets but should be administered under veterinary guidance.

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