Isotonicity - PowerPoint Presentation

Slide1

Isotonicity 1

Ian.Larson@monash.eduSlide2

Learning Objectives for these classes*

Define the term ‘

iso

-osmotic’

Define isotonic and differentiate from

iso

-osmotic

Explain the mechanism of action of hypertonic and hypotonic solutions on RBCs

Explain what strategies are used to make hypertonic and hypotonic solutions isotonic

Define

osmolarity

and osmolality

Be able to use equations involving

C

iso

%

, FD

1%

, and

SCE.

Describe how one

can

measure

isotonicity

of biological fluids

*in

addition

to:

Before our next class you need to be able toSlide3

Before our next class you need to be able to*:

Define a) hypertonic, and b) hypotonic

Explain why a solution containing 2

mM

glucose (impermeable) and 2

mM boric acid (permeable) is hypotonic to a solution containing 3 mM sucrose (impermeable).Explain what happens to red blood cells when they are immersed in a hypotonic solution or a hypertonic solutionCalculate Ciso for each of the classes of L

* not all the answers are in these notes, you might need to look elsewhereSlide4

For more information

Martin, “Physical Pharmacy,” second half of Chapter 8, i.e., ignore the section on buffered solutions (

eg

in 4

th

Ed, read from p. 180 on)Florence and Attwood, “Physicochemical Principles of Pharmacy” Ed 4, pp 69-75Slide5

Questions and FeedbackSlide6

Some

preparations that may require tonicity adjustment.

Injections, particularly IM( intra-muscular), SC (subcutaneous) and large volume IV (intravenous) injections

Eye drops

Eye lotions

Bladder irrigationsNose dropsSlide7

A solution with a higher concentration of impermeable solutes compared to red blood cells is said to be:

hypotonic

A:

hypertonic

B:

isotonic

C:

iso-osmotic

D:Slide8

Solution A contains 2

mM

sucrose (impermeable) and 3

mM

of urea (permeable); while solution B contains 5

mM dextrose (impermeable)A:A is hypotonic to BB:A is hypertonic to B

C:

A is isotonic to B

D:

A is iso-osmotic to BSlide9

Under isotonic conditions

L

iso

for a new drug is 2.0, therefore

C

iso isA:0.9B:3.85

C:

1.04

D:

0.26Slide10

A higher than usual Packed Cell Volume result means the blood cells were placed in a

A

hypotonic solution

B

hypertonic solution

C

iso-osmotic solution

D

isotonic solutionSlide11

Hypotonic solutions

Group discussion (5 minutes)

What would happen to red blood cells if they were immersed in a hypotonic solution?Slide12

Preparation of Isotonic Solutions

Hypotonic

solutions are usually made isotonic with body fluids by adding some

therapeutically inactive solute

.

e.g., dextrose or NaCl for intravenous use boric acid or NaCl for ophthalmic use Hypertonic solutions are usually made isotonic with body fluids by dilution with water.Slide13

Conditions for isotonicity

Solutions which are

iso

-osmotic

with body fluids are only considered to be isotonic if :membranes are impermeable to the solute (urea, boric acid, hexamine can pass thru RBC membranes)the solute does not alter the permeability of membranes (ethanol, some anaesthetics, and propylene glycol can increase the permeability)no chemical reaction leads to a change in the total concentration of dissolved ions or molecules.Slide14

Ciso

Rearranging

C

iso

= 0.52/ Liso In general, Liso may be grouped as1.9 for non-electrolytes2.0 for weak electrolytes3.4 for uni-univalent electrolytes, eg NaClHigher values for electrolytes of higher valencySo if know L

iso for class of additive can calculate isotonic concentration

So from before

ΔT

f

=

Lc

So under isotonic conditions

ΔT

f

=

L

iso

c

isoSlide15

Ciso example

Calculate

C

iso

for

NaCl, dextrose and boric acid.Liso (NaCl) = 3.4, Liso (dextrose) = 1.9, Liso (boric acid)

Ciso

= 0.52/

L

iso

The isotonic concentration of

NaCl

is 0.15 M,

of

dextrose

is

0.27 M, and

of

boric acid

is

0.29

MSlide16

Calculation of isotonic composition from freezing point data

A 1% solution of sodium chloride in water has a measured freezing point depression of 0.576

º

C,

i.e

, FD1% = 0.576º CWhat is the percentage composition of NaCl required in an aqueous solution to be isotonic with serum?Ciso NaCl = (0.52 /

0.576) x 1% from 1%

NaCl

= 0.576 °C

=

0.90%.

Δ

T

f

(

iso

)

= 0.52

°

C

This

is the accepted value (w/v) of a sodium chloride solution that is isotonic to body fluids.

Slide17

example

A 1% solution of

atropine

sulfate

in water has a measured freezing point depression of 0.07º C.What is the percentage of atropine sulfate required in an aqueous solution to be isotonic with serum?Ciso atropine sulfate

= (0.52 /

0.07)

x 1%

= 7.4%

Slide18

example – multi-component formulations

You are asked to make a 3% morphine

sulfate

(

C

iso = 6.5%) isotonic by adding NaCl. How much NaCl do you need?CisoNaCl = 0.9%, %NaCl = ?