Altering Product Strength Calculations PDF

Altering product strength, use of stock solutions, and Problem-solving by alligation Objectives Perform calculations for altering product strength by dilution, concentration, or fortification. Perform calculations for the preparation and use of stock solutions. Apply alli...

Altering product strength, use of stock solutions, and Problem-solving by alligation Objectives Perform calculations for altering product strength by dilution, concentration, or fortification. Perform calculations for the preparation and use of stock solutions. Apply alligation medial and alligation alternate in problem-solving.  The strength of a pharmaceutical preparation may be increased or decreased by changing the proportion of active ingredient to the whole. A preparation may be strengthened or made more concentrated by the addition of active ingredient, by admixture with a like preparation of greater strength, or through the evaporation of its vehicle, if liquid. The strength of a preparation may be decreased or diluted by the addition of diluent or by admixture with a like preparation of lesser strength Diluent: A substance added to a pharmaceutical product to reduce its strength, or dilute it. A diluents most often has no drug substance in it; examples are sterile water and petrolatum. Stock solution: A solution of a known concentration prepared for the convenience of dispensing; usually a strong solution from which weaker ones can be made conveniently.  In some case , you may receive a prescription in which you need to either dilute a product you have on hand or make a product more concentrated. These problems can generally be solved by: – Inverse proportion: – Using the equation: – Determining the quantity of active constituent (solute) needed and then calculating the quantity of the available solution (usually concentrated or stock solution) that will provide the needed amount of constituent.  Example: If 500 mL of a 15% v/v solution of methyl salicylate in alcohol is diluted to 1500 mL, what is the percentage strength v/v?  Example: If 50 mL of a 1:20 w/v solution of aluminum acetate is diluted to 1000 mL, what is the ratio strength w/v?  Example: How much 10% w/w (in grams) ammonia solution can be made from 1800 g of 28% w/w strong ammonia solution?  Example: How much (in milliliters) of a 1 : 5000 w/v solution of phenylmercuric acetate can be made from 125 mL of a 0.2% solution?  Example: How much (in milliliters) of a 1:400 w/v stock solution should be used to make 4 L of a 1 : 2000 w/v solution?  Example: How much (in milliliters) of a 1 : 400 w/v stock solution should be used in preparing 1 gal of a 1: 2000 w/v solution?  Example: How much (in milliliters) of a 1% stock solution of a certified red dye should be used in preparing 4000 mL of a mouthwash that is to contain 1 : 20,000 w/v of the certified red dye as a coloring agent?  Example: How much (in milliliters) of a 1 : 50 stock solution of ephedrine sulfate should be used in compounding the following prescription?  Example: Prepare 30 mL of a 5 mg/mL oral phenobarbital solution using phenobarbital available from the manufacturer in a 65 mg/mL solution that comes in 1-mL vials. How much stock solution will be required?  Example: Hydrocortisone is available in a vial of 100 mg in 2 mL. You are to prepare 24 mL of a 5-mg/mL hydrocortisone dilution using the available stock vials. How much hydrocortisone (in milliliters) and how much diluent (in milliliters) will you need?  Example: How much water (in milliliters) should be added to 300 mL of a 1 : 750 w/v solution of benzalkonium chloride to make a 1 : 2500 w/v solution?  Alligation Alligation is a method of solving problems that involves the mixing of solutions or mixtures of solids possessing different percentage strengths. Alligation medial: Calculation of the mixture of ingredients possessing different percentage strengths using the weighted average of the mixture, given the quantity and concentrations. Alligation alternate: This method allows calculation of the number of parts of two or more components of a given strength when they are mixed to prepare a mixture of a desired strength. Crosswise substraction is used to determine the amounts needed of each component.  Example: What is the percentage strength v/v of alcohol in a mixture of 3000 mL of 40% v/v alcohol, 1000 mL of 60% v/v alcohol, and 1000 mL of 70% v/v alcohol? Assume no contraction of volume after mixing.  Example: What is the percentage of zinc oxide in an ointment prepared by mixing 200 g of 10% ointment, 50 g of 20% ointment, and 100 g of 5% ointment?  In some problems the addition of a solvent or vehicle must be considered; therefore, it is necessary to add the volume of the solvent or the weight to the total. It is generally best to consider the diluent as having zero percentage strength. Example: What is the percentage v/v of alcohol in a mixture containing 500 mL of terpin hydrate elixir (40% v/v alcohol), 400 mL of theophylline sodium glycinate elixir (21% v/v alcohol), and sufficient simple syrup to make 1000 mL?  Example: In what proportion should alcohols of 95% and 50% strengths be mixed to make 70% alcohol? Note that the difference between the strength of the stronger component (95%) and the desired strength (70%) indicates the number of parts of the weaker to be used (25 parts), and the difference between the desired strength (70%) and the strength of the weaker component (50%) indicates the number of parts of the stronger to be used (20 parts).  Example: In what proportion should 20% benzocaine ointment be mixed with an ointment base to produce a 2.5% benzocaine ointment?  Example: How much 2.5% hydrocortisone cream (in grams) should be mixed with 360 g of 0.25% cream to make a 1% hydrocortisone cream?  Example: How much coal tar (in grams) should be added to 3200 g of 5% coal tar ointment to prepare an ointment containing 20% coal tar?  Example: Calculate the volume of 95% alcohol required to prepare 600 ml of 70% alcohol? Volume required = 600ml Percentage of alcohol required = 70 Percentage of alcohol used = 95 To produce required % of alcohol, 70 parts of 95% alcohol and 25 parts of water mixed. Quantity of 95% alcohol required = 600x70/95 = 442.10ml Quantity of water required = 600 x 25/95= 157.90ml.