part 18: ISOTONICITY

Hypotonic solutions

• Solutions that has the LOWER tonicity than serum and other body fluids

• <0.9% NaCl w/v

Swelling or Lysis

Cell effect of Hypotonic solutions

Hypertonic solutions

• Solutions that has HIGHER tonicity than serum and other body fluids

• >0.9% NaCl w/v

Shrinking or Crenation

Cell effect of Hypertonic solutions

Isotonic solutions

• Solutions that has the SAME tonicity as serum and other body fluids

• 0.9% NaCl w/v

Normal

Cell effect of Isotonic solutions

1. Class I methods

2. Class II methods

Methods of Adjusting Tonicity

Class I methods

Addition of NaCl or Tonicity Adjusting Agent

1. Cryoscopic method

2. Sodium chloride equivalent method

Class I methods

Class II methods

Addition of H20

1. White Vincent method

2. Sprowls method

Class II methods

Freezing Point Depression Method

Cryoscopic method is also known as?

Cryoscopic method

An amount of tonicity adjuster (e.g. sodium chloride) is added to drug solution such that the final freezing point lowering is that of blood or serum

0.76 g

Sample problem: ISOTONICITY

Calculate the amount of sodium chloride that is required to give 100 mL of a 1% solution of apomorphine hydrochloride isotonic with blood. The freezing point depression of 1% solution of apomorphine hydrochloride is 0.08°C

0.183 g NaCl

Sample problem: ISOTONICITY

How many grams of sodium chloride are needed to adjust 30mL of a 1% Phenylephrine solution to isotonicity. The freezing point depression of a 1% solution of phenylephrine HCl is 0.17°C

Sodium chloride equivalent method

In this method, the quantity of drug is multiplied by a factor, E, whose product is equal to the quantity of NaCl having similar osmotic pressure as that of the drug

• E-value: amount of sodium chloride which has the same osmotic effect as 1 gram of drug

E-value

Amount of sodium chloride which has the same osmotic effect as 1 gram of drug

Step 1: amount of the drug x E value

Step 2: 0.9% x volume of solution in mL

Step 3: Step 2- Step 1

** Step 4: Step 3 / E value of the tonicity adjusting agent

Steps of Sodium chloride equivalent method

0.204 g NaCl

Sample problem: ISOTONICITY

How many grams of NaCl should be used in compounding the following prescription?

Rx 1

Pilocarpine nitrate (E=0.22) 0.3 g

NaCl q.s.

Purified water q.s. ad. 30 mL

Make isotonic solution

Sig for eyes

1.08 g of Boric Acid

Sample problem: ISOTONICITY

How many grams of boric acid should be used in compounding the prescription?

Rx 2

Phenacaine HCl (E= 0.17) 0.6 g

Chlorobutanol (E=0.18) 0.3 g

Boric acid (E=0.52) qs

Purified water q.s. ad. 80 mL

Make isotonic solution

Sig one drop in each eye

White Vincent Method

• USP method

• This method calculates the volume of an isotonic solution of a drug that can be prepared by dissolving the drug in a proper amount of water

• V = Weight (grams) x E value x 111.1

11.1 mL

Sample problem: ISOTONICITY

Chloramphenicol (MW 323.13 g/mole, Liso =2) 1g

Sterile water for injection, q.s. ad 100 mL

M. ft. isotonic solution

*Use E value of 0.10

18 mL

Sample problem: ISOTONICITY

Make the following preparation solution isotonic with respect to an ideal membrane.

Phenacaine hydrochloride 0.06 g

Boric acid 0.30 g

Sterilized distilled water q.s. 100.0 mL

(E for boric acid = 0.50, E for phenacaine hydrochloride = 0.20)

Martin-Sprowls Method

Sprowl’s method is also known as?

Sprowl’s method

• Simplified version of White Vincent Method

• V= 0.3g x E x 111.1

V = Weight (grams) x E value x 111.1

Formula of White Vincent Method

• Formula of E value: E = 17 x (Liso/MW)

V= 0.3g x E x 111.1

Formula of Sprowls Method