Dear Colleagues, Mathematical calculations play a vital role in formulating and preparing magistral formulations prescribed on prescriptions. For a pharmaceutical preparation to exhibit the desired effect, it is essential that the amount, dose, and concentration of the active substance it contains are accurately calculated and prepared according to its formula.
In this article, you will see examples of diluting stock solutions commonly encountered in Pharmaceutical Technology, such as formaldehyde, silver nitrate, aluminum subacetate, and hydrogen peroxide.
To recall the definition of a stock solution: it is a prepared solution form of an active substance. Such mixtures are prepared by dissolving that substance in a suitable solvent.
DILUTION OF STOCK SOLUTIONS
General Formula:
Based on the formula M1xV1=M2xV2
M1=Concentration of the solution to be prepared (dilute solution).
V1=Volume of the solution to be prepared.
M2=Concentration of the stock solution used to prepare the desired solution.
V2=Amount to be taken from the concentrated solution, to be calculated.
Example 1: Using Officinal Formaldehyde solution, prepare 150 g of Formaldehyde solution at a 15% (w/w) concentration.
Formaldehyde solution-Soluté de formaldéhyde-Solutio formaldehydi
According to the Turkish Pharmacopoeia (1974), it should contain not less than 35.0% (w/w) and not more than 36.5% (w/w), or not less than 38.0% (w/v) and not more than 40.00% (w/v) formaldehyde. In the Turkish Codex (T.K. 1954), the concentration of Formaldehyde solution is stated as “contains at least 35 percent formaldehyde (HCHO)”. In this case, a 35% (w/w) concentration is understood.
15×150/35=64.28 g of formaldehyde solution is taken and made up to 150 grams with distilled water.
Example 2: Prepare 75 ml of a solution at a concentration of 0.25% (w/v) using a 2% (w/v) silver nitrate solution.
0.25×75/2=9.37 ml is taken and brought up to 75 ml with distilled water.
Example 3: Prepare 150 g of Sol. Sous-acétate d’aluminium at a (4%) concentration.
Aluminum subacetate solution-Soluté de sous-Solutio Aluminii Subacetatis T.K.(1954)
According to T.K. (1954), it contains at least 8.5% aluminum subacetate. After the preparation is prepared, assay/dosing should be performed, and the amount of aluminum subacetate contained in the preparation and the control date must be recorded on the label. More dilute aluminum subacetate solutions can be prepared using this stock solution.
4×150/8.5=70.58 g is taken from the aluminum subacetate solution and completed to 150 g with distilled water.
Example 4: Prepare 300 ml of Eau oxygénée at a 3% (w/v) concentration from Perhydrol solution.
Concentrated hydrogen peroxide solution-Soluté concentré de peroxyde d’hydrogène-PERHYDROL T.K.(1954) and Turkish Pharmacopoeia (1974)
According to the Turkish Pharmacopoeia (1974), concentrated hydrogen peroxide solution (Perhydrol) is at a 30% (w/v) concentration and is described as 100 volume.
3×300/30=30 ml Using a graduated cylinder, 30 ml of perhydrol is taken (equivalent to 9 g of pure hydrogen peroxide) and made up to 300 ml with distilled water.
Example 5: Prepare 250 ml of (5 vol) hydrogen peroxide solution from Perhydrol solution.
Hydrogen peroxide solution-Soluté de peroxyde d’hydrogène-EAU OXYGENEE-Solutio hydrogenii peroxidi
According to the Turkish Pharmacopoeia (1974), it contains 3–3.2% (w/v) hydrogen peroxide and is practically described as 10 volume (10 vol).
Preparation: It is obtained by dilution with water from solutions containing a hydrogen peroxide amount higher than 3% (w/v). For example, 1 ml is taken from a 30% (w/v) concentrated hydrogen peroxide solution (100 vol) and diluted to 3% (w/v) by adding 9 ml of water.
According to T.K. (1974), perhydrol 30% (w/v) = 100 volume. The amount to be taken for 250 ml of 5 volume solution;
5×250/100=12.50 ml of perhydrol is taken and made up to 250 ml with water.
Source:
Prof. Dr. Şükran GEÇGİL
Calculations in Drug Formulation
Wishing you a good week…
Spec. Pharm. Ahmet Nezihi Pekcan
Pekcan Pharmacy – Konya
[email protected]
Tel: (332) 3520657
http://www.majistralformul.com/
