pH, Buffers and Isotonic Solutions
179
Class IT Methods
8.11. 3 White Vincent Method Class II methods for calculating
tonicity involve adding water to the drugs to make an isotonic
solution. This is followed by the addition of an isotonic or isotonic buffered diluting vehicle to adjust the solution to the final volume.
White -Vincent
developed
a simplified
equation
for
calculating the volume V (mls) which can be written as (eq 8.35)
V=w*E*111.1 Where V is volume of isotonic solution (ml) prepared by mixing drug with water w is weight of the drug (gm) E is sodium chloride equivalent of drug
111.1 is a constant denotes volume of isotonic solution in millilitres obtained when 1 g sodium chloride is dissolved in water. If more than one ingredient is used in isotonic preparation,
the volume of isotonic solution V can
be calculated as V = [ (WI x El)
+ (W2 x Ez) + ---------+ (w, x EJ ] x 111.1
(eq 8.36)
olved problem ercise 8.8: Make the following prescription
isotonic with tears
Ephedrine Sulphate - 0.06 g Boric acid- 0.30 g Sterilized distilled water q.s. 100 ml for ephedrine sulphate-0.23, Solunon
E for boric acid-0.52)
V = [(0.06 x 0.23) Ans. V
+ 0.3 x 0.52)] x 111.1
= 19 ml
g are mixed with water to make 19 ml of isotonic solution and preparation issolution. o olume of 100 ml by adding isotonic dilute solution