Module 5: Alterations of Concertation
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 (API) (solute)
Admixture with a like preparation of greater strength
Evaporation of its vehicle, if liquid.
The strength of a preparation may be decreased or diluted by the
Addition of diluent (solvent)
By admixture with a like preparation of lesser strength.
The reduction in the strength based on the
patient's age (e.g., pediatric or elderly)
medical status (diseases state),
to assess a patient's initial response to a new medication
The strengthening of a product
to meet the specific medication needs of an individual patient (check on the lowest possible medication, then increase gradually, 5 mg -> 10 mg)
Alteration of the strength of pharmaceutical preparations
Reduction and enlargement of formula
Most of the pharmaceutical preparations are based on official formulas from USP or NF and other compendium which are generally in 1000 mL or 1000 grams.
In the course of pharmaceutical practice such as in small-scale compounding, this requires only minute quantities such as 15 mL, or 10 grams, thus reducing the amount of each ingredient is necessary.
In industrial setting, formulas may be scaled up to quantities of ingredients sufficient to prepare hundreds of thousands of dosage units in a production batch.
In any of these situations, the correct proportion of each ingredient to one another should be ensured.
There are two methods employed in reducing and enlarging formulas: (1) ratio and proportion method; and (2) factor method.
2. • 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 (API) (solute)
• Admixture with a like preparation of greater strength
• Evaporation of its vehicle, if liquid.
• The strength of a preparation may be decreased or diluted by the
• Addition of diluent (solvent)
• By admixture with a like preparation of lesser strength.
3. ALTERATIONS OF CONCENTRATION
• The reduction in the strength based on the
• patient's age (e.g., pediatric or elderly)
• medical status (diseases state),
• to assess a patient's initial response to a new medication
• The strengthening of a product
• to meet the specific medication needs of an individual patient (check on
the lowest possible medication, then increase gradually, 5 mg -> 10 mg)
• Alteration of the strength of pharmaceutical preparations
• Reduction and enlargement of formula
5. • Most of the pharmaceutical preparations are based on official formulas from
USP or NF and other compendium which are generally in 1000 mL or 1000
grams.
• In the course of pharmaceutical practice such as in small-scale compounding,
this requires only minute quantities such as 15 mL, or 10 grams, thus
reducing the amount of each ingredient is necessary.
• In industrial setting, formulas may be scaled up to quantities of ingredients
sufficient to prepare hundreds of thousands of dosage units in a production
batch.
• In any of these situations, the correct proportion of each ingredient to one
another should be ensured.
• There are two methods employed in reducing and enlarging formulas: (1)
ratio and proportion method; and (2) factor method.
6. RATIO AND PROPORTION METHOD
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑖𝑛𝑔𝑟𝑒𝑑𝑖𝑒𝑛𝑡
𝑇𝑜𝑡𝑎𝑙 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦
=
𝑥 𝑛𝑒𝑒𝑑𝑒𝑑
𝑇𝑎𝑡𝑎𝑙 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑑𝑒𝑠𝑖𝑟𝑒𝑑
7. • In some formulas, the quantities of ingredients are given in proportional parts rather than
in weights or volumes.
• The “parts” in solid or semisolid ingredients may be considered as “grams”, whereas the
liquid ingredients may be considered as “milliliters”.
FACTOR METHOD
Step 1: Determine the factor that defines the multiple or the decimal fraction of the
amount of formula to be prepared using the equation below:
Step 2: Multiply the quantity of each ingredient in the formula by the factor to
determine the amount of each ingredient required in the reduced or enlarged formula.
8. 1. Use the official formula below, calculate the amount of each ingredient
needed to make 240 mL of Peppermint Spirit using the ratio and proportion
method.
Rx No. 1
PEPPERMINT SPIRIT
Peppermint oil........…………………100 mL
Peppermint powder.…..………..…10 g
Alcohol, qs ad..........…………………1000
mL
Calculation:
Ingredients
Quantity for 1000
mL
Quantity for 240
mL
Peppermint oil 100 mL 24 mL
Peppermint
powder
10 g 2.4 g
Alcohol, qs ad 1000 240 mL
9. 2. Use the formula below, calculate the amount of each ingredient to make 1000
grams from the formula expressed in proportional parts.
Rx No. 2
COAL TAR OINTMENT
Coal Tar..............…............………… 5 parts
Zinc Oxide....................……………10 parts
Hydrophilic Ointment.…………...50 parts
Calculation:
1. Get the total number of parts. This represents the total
weight of the preparation ( _____ parts = 1000 g).
2. Use the ratio and proportion method and compute the
quantity of each ingredient.
1. Total number of parts: 5 parts + 10 parts + 50 parts = 65 parts = 1000 g
2. Amount of each ingredient:
Ingredients Parts
Metric quantity
for 1000 g
Coal tar 5 parts 76.92 g
Zinc oxide 10 parts 153.85 g
Hydrophilic
ointment
50 parts 769.23 g
TOTAL 65 parts 1000 g
11. • The strength of a pharmaceutical preparation may be increased or decreased by
changing the proportion of active ingredient to the whole.
• A preparation must 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 (direct heat or steam
bath).
• 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.
• Here are some alternative methods of calculation for the alteration of the
strength of pharmaceutical preparation:
12. 1. DILUTION AND CONCENTRATION OF LIQUIDS
Quantity X Concentration = Quantity X Concentration
• Quantity - must be in mL
• Concentration - must be in %
(concentrated) (diluted)
13. 2. STOCK SOLUTIONS
• These are solutions of known concentrations that are prepared by the pharmacist
for convenience in dispensing.
• They are usually strong solutions from which weaker ones may be made
conveniently.
• Their concentration is expressed as ratio strength.
• The same formula for dilution and concentration of liquids may be used.
• However, the ratio strength must be changed to % strength.
14. 3. DILUTION OF ACIDS
• The % strength of concentrated acid is expressed as % w/w while
the concentration of dilute acid is expressed as % w/v.
• To determine the volume of concentrated acid to be used in preparing
a diluted acid requires the specific gravity of the concentrated acid.
15. Strengths of Acids
Glacial acetic acid 100%w/w
HCl 37%w/w
H2SO4 96%w/w
HNO3 65%w/w
H3PO4 85%w/w
Dilute HCl 10%w/v
Dilute glacial acetic acid 6% w/v
Wt. of acid = volume x % (in decimal)
Q X C = Q X C
Vol. of acid = weight of acid / sp. gr of acid
16. 4. DILUTION AND FORTIFICATION OF SOLIDS
Q1 X C1 = Q2 X C2
• Quantity - expressed in g
• Concentration - expressed in %
17. 5. TRITURATIONS
• Triturations are dilutions of potent
medicinal substances.
• (1:10 w/v or 10% w/v mixtures) they are
prepared by diluting 1 part of the drug
with 9 parts of finely powdered
lactose.
• Problems on trituration are solved by
ratio and proportion.
• 1: 10 :: weight of drug: weight of
mixture
18. 6. ALLIGATION MEDIAL
• It is a method for calculating the average concentration of a mixture
of two or more substances possessing different % strength.
Quantity x % strength = Product
Average % = Total Product / Total Quantity
19. • Prepare 500 mL of 80% ethanol from 95% ethanol
95% 80 parts
80%
0% 15 parts
= 95 parts
Amount of 95% ethanol
= 95 parts : 500 mL :: 80 parts : x mL
= 500 mL (80 parts) / 95 parts
= 421 mL of 95% ethanol
Amount of water:
= 95 parts : 500 mL :: 15 parts : x mL
= 500 mL (15 parts) / 95 parts
= 79 mL of water
20. 7. ALLIGATION ALTERNATE
• It is a method for calculation of the number of parts of two or more
components of known concentration to be mixed when the final
desired concentration is known.
21. • The methods of alligation medial and alternate can also be used to
solve problems that involved specific gravity.
Specific gravity x volume = product
Average specific gravity = Total product / Total volume
