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Isotonic solutions
Osmosis: "solvent passage through semi permeable membrane from dilute solution to a more concentrated solution (diffusion).
Isotonicity adjustment methods 1] Class I methods 2] Class II methods Sodium chloride or some other substance is added to the solution of the drug to lower the freezing point of the solution to – 0.52⁰C and thus make it isotonic with body fluids. Water is added to the drug in a sufficient amount to form an isotonic solution then the preparation is brought to its final volume with an isotonic solution. Involves: 1.Cryscopic or freezing point depression method. Involves: 1.White-Vincent method.
freezing point depression methodF r e e z i n g p o i n t d e p r e s s i o n i s a c o l l i g a t i v e p r o p e r t y ( d e p e n d o n n u m b e r o f m o l e c u l e s p r e s e n t ) . T h e f r e e z i n g p o i n t o f b o t h h u m a n b l o o d a n d l a c h r y m a l f l u i d i s - 0 . 5 2 ° c . I f w e d i s s o l v e s o l i d s i n w a t e r t i l l f r e e z i n g p o i n t d e p r e s s i o n i s 0 . 5 2 i t w i l l b e i s o t o n i c w i t h b l o o d A n y s o l u t i o n h a s t h e s a m e f r e e z i n g p o i n t i s i s o t o n i c w i t h b o t h ( h a v e t h e s a m e o s m o t i c p r e s s u r e ) . F . P . D o f 1 % s o l u t i o n = t f 1 % = f r e e z i n g p o i n t d e p r e s s i o n o f 1 % s o l u t i o n
Steps to solve F.P.D% of drug in prescription Calculate F.P.D. of each drug Calculate total F.P.D calculate required F.P.D (0.52-Total F.P.D.) Cal % of NaCl or any other substance needed to be added
Example. 1: What proportion of procaine hydrochloride will yield a solution isotonic with blood plasma? F.P.D. of 1% W/V solution of procaine HCl is 0.122. Solu: 1% 0.122 x 0.52 X= 4.26%
Example. 2: The freezing point of a 5% solution of boric acid is 1.55oC. How much boric acid should be used in preparing 1000 ml of an isotonic solution? Solu: 5% 1.55 x 0.52 X= 1.677% 1.677 100 ml Y 1000 ml Y=16.77 g
Example. 3: How much sodium chloride is required to render 100 ml of 1% solution of Apomorphine hydrochloride isotonic with blood serum? F.P.D. of 1% solution Apomorphine hydrochloride 0.08oC and F.P.D. of 1% solution of sodium chloride 0.58oC Solu: % of drug in prescription 1% F.P.D. of apomorphine =0.08 Total F.P.D =0.08 Required F.P.D= 0.52- 0.08= 0.44 1% NaCl 0.58 x 0.44 X= 0.75%
Example 4 freezing point depression of 1% W/V solution of cocaine hydrochloride is 0.09 °C and the freezing point depression of 1% W/V solution of sodium chloride is 0.576 °C What concentration of cocaine hydrochloride will yield a solution iso osmotic with blood plasma? What is the amount of cocaine HCl required to render the solution isotonic ? Solu 1% 0.09 X 0.52 X=5.78% cocaine HCL 5.78g 100 ml Y 100 ml Y=5.78
Example 5 How much sodium chloride should be used in compounding the following prescription. R/ Cocaine Hydrochloride 1.3g Sodium chloride Q.S. Water to 100 ml Make isotonic solution where ΔTf 1% of cocaine hydrochloride is 0.09 °C and ΔTf 1% of sodium chloride is 0.576 °C
Solu Cocaine Hydrochloride 1.3g F.P.D. of 1% = 0.09 Sodium chloride Q.S F.P.D. of 1% = 0.576 Water to 100 ml % of cocaine = 1.3g in 100 ml = 1.3% F.P.D of 1.3% is: 1% 0.09 1.3 x X=0.117 Total F.P.D= 0.117 Require F.P.D =0.52-0.117= 0.403 Amount of NaCl required: 1% NaCl 0.576 Y 0.403 Y =0.699% Volume of prescription =100 0.699 100 Z 100 Z=0.699g
Example 6 R/ Sulfacetamide sodium 3 g. Sodium bisulphite 500 mg. Sodium chloride Q.S Water to 200 ml • 1% solution of sulfacetamide makes F.P.D by 0.14. • 1% solution of sodium bisulphate makes F.P.D by 0.36. Mention if the following prescription is isotonic or not if not find how many grams of sodium chloride are required to render the following prescription isotonic?
Isotonicity adjustment methods 1] Class I methods 2] Class II methods Sodium chloride or some other substance is added to the solution of the drug to lower the freezing point of the solution to – 0.52⁰C and thus make it isotonic with body fluids. Water is added to the drug in a sufficient amount to form an isot onic solution then the preparation is brought to its final volume with an isotonic solution. Involves: 1.Cryscopic or freezing point depression method. Involves: 1.White-Vincent method.
NoteIsotonic solution can be produced by several isotonic solutions added together A B C D DA B C
The method involves 2 steps: 1. Calculate the volume of water to be added to the solid ingredient of the prescription to make an isotonic solution using the equation: V = W x E x 111.1 Where; V is the volume of water to be added to make an isotonic solution. W is the weight of the substance in grams E is the sodium chloride equivalent of the substance. Note: The sodium chloride equivalent (E) of a drug: "is the amount of sodium chloride that has the same osmotic effect as 1 gram of the drug 2. Subtract the volume in step 1 from the final volume of the prescription to calculate the amount of the isotonic or isotonic-buffered diluting vehicle to be added to complete the volume. White-Vincent method:
Example 1 How many mls of distilled water should be used in compounding the following prescription? Where NaCl equivalent of pilocarpine nitrate is 0.22. sodium chloride solution (0.9%) is isotonic R/ Pilocarpine nitrate 0.3 g Distilled water Q.S. Sodium chloride solution (0.9%) to 30 ml Make isotonic solution Sig. for the eye Solu V = W x E x 111.1 = 0.3 x 0.22 x 111.1 = 7.3326
Example 2 How many mls of isotonic dextrose solution should be used in compounding the prescription? Use the White-Vincent method. R/ Ephedrine Hydrochloride 0.5g (E = 0.3( Chlorobutanol 0.25g (E = 0.24( Isotonic dextrose solution Q.S. ad100.0 ml Sig. Nasal drops.
Solu Step 1: Volume of water to be added= 16.665 + 6.666 = 23.331 ml water Step 2 Total volume – volume of water = 100 - (16.665 + 6.666) = 76.669 ml isotonic dextrose Ephedrine Chlorobutanol V1 = W x E x 111.1 V2 = W x E x 111.1
Example 3 R/ Ingredient Z (E = 0.18) 2% Sterile preserved water q.s to make 30 ml Isotonic acetate buffer How many milliliters of purified water and how many milliliters of isotonic acetate buffer should be used in compounding the prescription?
Solu Weight of ingredient Z 2g 100 ml X 30 ml X= 0.6 g Step 1: V = W x E x 111.1 = 0.6 x 0.18 x 111.1 = 11.99 ml H2O Step 2 Total volume – volume of water = 30 - 11.99 = 18 ml isotonic acetate buffer
Example 4 R/ Pilocarpine nitrate (E = 0.23) 0.5% Boric acid (E = 0.52) 155mg Sterile water for injection q.s to make 30 ml Make isotonic sol. Sig. one drop in each eye You have on hand an isotonic acetate buffer solution How many milliliters of purified water and how many milliliters of isotonic acetate buffer should be used in compounding the prescription?
Solu Step 1: Volume of water to be added = 3.82 + 8.95= 12.78 ml Step 2 Total volume – volume of water = 30 - (3.82 + 8.95) = 17.21 ml isotonic acetate buffer Pilocarpine Boric acid Weight of pilocarpine Weight of boric acid V1 = W x E x 111.1 V2 = W x E x 111.1
Thank youRokaia Shabana