Electrolytes Used in Replacement Therapy and ORS


Electrolyte replacement therapy is a fundamental aspect of medical treatment, aiming to correct imbalances in essential ions within the body. It involves replenishing specific electrolytes to restore health and maintain homeostasis. Under the normal physiological conditions body mechanisms adjusts the electrolyte balance and no replacement is necessary. However, due to certain conditions (like pathological or disease), electrolytes may become deficient in body. Administration of that electrolyte in appropriate concentration of tonicity becomes necessary. In this article we will see some electrolytes used in replacement therapy.

There are various organic and inorganic compounds present in the body. There is various regulatory mechanism which control the ionic balance, osmotic balance and pH of body fluids. If the body cannot maintain or correct the electrolyte balance, then it is balanced by external administration, which is known as replacement therapy.

Sodium chloride

Molecular wight: 58.54

Preparation: Industrially it is obtained by evaporation of sea water and by purifying rock salt. In laboratory it can be obtained by passing hydrochloric acid gas in aqueous solution of common salt, then crystals precipitated out.

Physical Properties

  • White crystalline powder
  • Colourless crystals
  • Odourless
  • Saline taste
  • Freely soluble in water
  • Soluble in glycerine

Chemical properties

  • It gives white water-soluble precipitate of silver chloride when aqueous solution is treated with solution of silver nitrate.

NaCl + AgNO3 — > AgCl + NaNO3

  • It can be oxidised chemically using H2SO4 and liberates chlorine gas.

2Cl+ MnO2 + 2H2SO4 — > Mn++ + SO4 + 2H2O + Cl2


Earlier it was analysed by precipitation titration technique using Mohr method, in which aqueous solution is directly titrated with standard silver nitrate solution using potassium chromate as indicator.

Nowadays it is analysed by Volhard’s precipitation method. In this method aqueous solution is acidified with nitric acid and some excess of standard silver nitrate is added. When silver chloride is precipitated, the nitrobenzene is added and excess of silver nitrate is determined by titrating with standard ammonium thiocyanate using ferric ammonium sulphate as indicator.

It contains not less than 99.5% and not more than 100.5% of NaCl, calculated with reference to substance dried at 1300c.


  • Preparation of hypertonic solution.
  • As an electrolyte replacement alone or combination with other salts.
  • In case of poisoning, it is used as a first aid.
  • In dialysis fluid.
  • It is a constituent of ringer solution and ORS.

Official preparations

Official preparationComposition of NaCl
Sodium chloride eye lotion BP0.85 – 0.95% w/v
Sodium chloride solution BP0.9% w/v
Sodium chloride injection IP0.85 – 0.95% w/v
Sodium chloride hypertonic injection IP1.52 – 1.68% w/v
Sodium chloride tablet BP95 -105% w/v of the stated amount
Sodium chloride and dextrose injection IP0.11, 0.18, 0.2, 0.225, 0.3 and 0.33 % of NaCl with 5% of dextrose


0.45% NaCl with 2.5% 5% and 10% of dextrose


0.9% of NaCl with 2.5%, 5%, 10% and 25% of dextrose

Mannitol and sodium chloride injection USP5% and 10% mannitol with 0.3% NaCl


15% and 20% of mannitol with 0.45% NaCl

Potassium chloride

Molecular weight: 74.55


It is obtained from natural mineral called, carnallite (KCl.MgCl2.6H2O). The raw salt is treated with hot water, less soluble crystals of KCl comes out of mother liquor.

In laboratory, it can be prepared by the action of HCl on potassium carbonate or bicarbonate.

KHCO3 + HCl — > KCl + H2O + CO2


  • Colourless prismatic or cubical crystals
  • Sometimes white granular powder
  • Odourless
  • Saline in taste
  • Freely soluble in water
  • Neutral to litmus


As per IP, it is analysed by Mohr method, in which the aqueous solution is directly titrated with standard silver nitrate solution using potassium chromate as indicator.


  • Oral replacement of potassium
  • Used as adjunct in treatment of myasthenia gravis
  • Constituent of ringer solution and ORS
  • In the treatment of hypokalaemia

Official preparations

Potassium chloride and glucose IV infusion BP0.15, 0.2 and 0.3% w/v of KCl with 5% w/v of glucose
Potassium chloride and sodium chloride infusion BP0.15, 0.2 and 0.3% w/v of KCl with 0.9% w/v of NaCl
Potassium chloride, sodium chloride and glucose IV infusion BP0.15, 0.2 and 0.3% w/v of KCl each containing 0.18% w/v of NaCl and 4% w/v of glucose.

Calcium gluconate

Molecular weight:430


It can be prepared by following two methods.

  • By the oxidation of glucose to gluconic acid in the presence of calcium carbonate. The oxidation of glucose is affected either by bromine or by electrolytic oxidation in presence of sodium bromide.
  • By preparing gluconic acid and then adding calcium carbonate to form the salt. In this case, the gluconic acid is usually obtained by the action of various moulds or bacteria of the Acetobacter group on glucose.


  • Crystalline or granular powder
  • Odourless
  • Tasteless
  • Stable in the air
  • Sparingly soluble in water
  • Insoluble in alcohol

Incompatibilities: It is incompatible with oxidising agents and solution of calcium gluconate gives a precipitate with oxalates or borates.


It is assayed by direct complexometric titration methods involving replacement with magnesium, using 5ml of standard magnesium sulphate solution. The pH is adjusted with ammonia-ammonium chloride buffer. The volume of disodium edetate equivalent to magnesium sulphate solution is substrated from total disodium edetate used and then results are calculated.


  • Source of calcium in calcium deficiency
  • Drug of choice for severe hypocalcemic tetany
  • In cases of hypermagnesemia (high blood levels of magnesium), calcium gluconate is administered intravenously.
  • Used during cardiac arrest resuscitation to strengthen the heart muscle.

Official preparations

  • Calcium gluconate injection: It contains quantity of calcium equivalent to not less than 8.5% and not more than 9.4% of the stated amount of calcium gluconate.
  • Calcium gluconate tablets: Each average weight of the tablet contains not less than 95% and not more than 105% of the stated amount of calcium gluconate on the label.

Oral Rehydration Salts (ORS)

Oral Rehydration Solution (ORS) plays a crucial role in electrolyte replacement therapy. ORS is a powder containing electrolytes designed to rehydrate the body when it experiences dehydration due to conditions like diarrhoea. It contains a specific combination of water, sugar, and electrolytes, particularly potassium and sodium. ORS preparation may contain flavouring agent and a suitable agent for free flow of powder. The goal of oral rehydration therapy is to replenish fluid levels in the body. When we lose fluids due to diarrhoea or other causes, our electrolyte balance gets disrupted. ORS helps restore this balance. By providing essential electrolytes (such as sodium and potassium) along with glucose, ORS helps maintain proper hydration.

WHO and UNICEF recommend using ORS alongside zinc for effective diarrhoea treatment. ORS is a simple yet powerful solution that helps save lives by preventing severe dehydration. ORS is a valuable tool in managing dehydration, especially in situations where fluid loss can be life-threatening.

ORS can be prepared by using one of the following formulae. The formula II and III are recommended by WHO and UNICEF for control of diarrhoeal diseases. The quantities given below are for the preparation of 1 litre solution.

Ingredient Formula IFormula IIFormula III
Sodium chloride1.0g3.5g3.5g
Potassium chloride1.5g1.5g1.5g
Sodium bicarbonate1.5g2.5g
Sodium citrate2.9g
Anhydrous glucose36.4g20.0g20.0g


Electrolyte replacement therapy is crucial for maintaining health and homeostasis. It involves correcting imbalances in essential ions within the body. Key electrolytes include sodium (Na+), chlorine (Cl-), potassium (K+), bicarbonate (HCO3-), calcium (Ca2+), and magnesium (Mg2+). These electrolytes play vital roles in fluid balance, nerve function, pH regulation, muscle contraction, and bone health. Solutions containing these electrolytes are used to restore balance and prevent complications in conditions like dehydration and diarrhoea.

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