Reducing and enlarging formulas

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Reducing and enlarging formulas
Dr. Osama A. A. Ahmed
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Reducing and enlarging formulas

• Factor (F) Amount desired/ amount of formula
• From the following formula, calculate the
  quantity of each ingredient required to make 240
  ml of calamine lotion
• Calamine
  80 g
• Zinc Oxide
  80 g
• Glycerin
  20 ml
• Bentonite magma
  250 ml
• Lime water (Calcium Hydroxide) to
  1000 ml
• Factor (F) 240/1000 0.24
• 
  X 0.24
• Calamine 80 g
  19.2 g
• Zinc Oxide 80 g
  19.2 g
• Glycerin 20 ml
  4.8 ml
• Bentonite magma 250 ml
  60 ml
• Lime water to 1000 ml
  to make 240 ml

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Dilution, Concentration and Alligation

• Factor (F) Amount desired/ amount of formula
• From the following formula, calculate the
  quantity of each ingredient required to make 1000
  g of the ointment
• Coal tar 5
  parts
• Zinc Oxide 10
  parts
• Hydrophilic ointment 50 parts
• Total number of parts 65
• 1000 g will contain 65 parts
• Factor (F) 1000/65
• 
  X
  1000/65
• Coal tar
  5 parts 76.92 g
• Zinc Oxide 10
  parts 153.85 g
• Hydrophilic ointment 50 parts
  769.23 g

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Selected calculation in contemporary compounding

• Constitution of dry powders for oral solution or
  suspension
• Some drugs as antibiotics lose their potency in a
  relatively short period when prepared in a liquid
  dosage form.
• Example the label of dry powder package of
  cefprozil (CEFZIL) for oral suspension directs
  the pharmacist to add 72 ml of purified water to
  prepare 100 ml of suspension. If the package
  contains 2.5 g of cefprozil, how many milligrams
  of the drug would be contained in each
  teaspoonful dose of the constituted suspension?
• 2.5 g 2500 mg
• 2500 mg 100 ml
• X mg 5ml
  X 125 mg cefprozil

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Selected calculation in contemporary compounding

• Example the label of a dry powder for oral
  suspension states that when 111 ml of water are
  added to the powder, 150 ml of a suspension
  containing 250 mg of ampicillin per 5 ml are
  prepared. How many milliliters of purified water
  should be used to prepare, in each 5 ml of
  product, the correct dose of ampicillin for a
  60-lb. child based on the dose of 8 mg/kg of body
  weight?
• 1 kg 2.2 lb
• X kg 60 lb
  X 60/2.2 27.273 kg
• ampicillin dose 27.273 X 8 218
  mg
• Total amount of ampicillin in the container
• 250 mg 5 ml
• X mg 150 ml
  X 7500 mg
• The new volume to be prepared
• 218 mg 5 ml
• 7500 mg X ml
  X 172 ml
• As the dry powder occupies 39 ml (150 ml 111
  ml ), so the amount of water added is
• Amount of water 172 39 ml 133 ml

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Selected calculation in contemporary compounding

• Constitution of dry powders for parenteral
  solution
• Example Using a vial containing 200,000 units of
  penicillin G potassium, how many milliliters of
  solvent should be added to the dry powder in
  preparing a solution having a concentration of
  25,000 units/ ml?
• 25,000 units 1
  ml
• 200,000 units X ml
  X 8 ml
• Use of prefabricated dosage forms in compounding
• Example Only capsules, each containing 25 mg of
  indomethacin, are available. How many capsules
  should be used to obtain the amount of
  indomethacin needed in preparing the following
  prescription?
• R/ Indomethacin 2 mg/ml
• Cherry syrup ad 150 ml
• Sig. 5 ml b.i.d
• Amount of indomethacin needed in the prescription
  150 X 2 300 mg
• 1 capsule
  25 mg
• X capsules
  300 mg X 12 capsules needed