فنون الحسابات الصيدلانية
Pharmaceutical compounding calculations
ان تحضير معظم وصفات التركيبات يحتاج الى إلمام بالحسابات الصيدلانية
و حتى في اكثر العمليات الحسابية بساطة فإن اهمال الارقام العشرية بعد الفاصلة او وضع قيم تقريبية .. ممكن ان يكون لها آثار خطيرة و قد تكون قاتلة .
و حتى في اكثر العمليات الحسابية بساطة فإن اهمال الارقام العشرية بعد الفاصلة او وضع قيم تقريبية .. ممكن ان يكون لها آثار خطيرة و قد تكون قاتلة .
فعندما نريد تحويل وحدة قياس الى وحدة قياس اخرى يجب استخدام القيمة المطابقة و ليست التقريبية ..
Ex.
The correct metric equivalent value for 1fl oz is 29.57 ml, not 30ml or even 29.6 ml.
The correct metric equivalent value for 1fl oz is 29.57 ml, not 30ml or even 29.6 ml.
Measurement systems:
The metric system is the official system of measurement used in pharmacy and medicine.
The metric system is the official system of measurement used in pharmacy and medicine.
Least measurable quantity of weight:
A pharmacy’s tortion balance has a sensitivity reading of 5 mg. what is the smallest quantity that can be accurately weighed with a maximum error of 5%?.
A pharmacy’s tortion balance has a sensitivity reading of 5 mg. what is the smallest quantity that can be accurately weighed with a maximum error of 5%?.
a//// 100% X {maximum potential error (sensitivity reading) / permissible error (in percent)} =least measurable quantity.////a
a//// x= 100% X (5mg / 5%) = 100mg. ////a
Density factors in weighing /measuring:
A pharmacist receives a prescription for 120 ml of a 3% (w/v) hydrochloric acid (Hcl) solution. The density of concentrated hydrochloric acid (37 % w/w) is 1.18 g/ml. how many milliliters of the concentrated acid would be required for the prescription?
Step 1: calculate the weight of the required quantity of the 3% Hcl solution:
a//// 3 %( w/v) =0.03 g/ml. ////a
a//// 0.03 g/ml x 120 ml =3.6 g. ////a
A pharmacist receives a prescription for 120 ml of a 3% (w/v) hydrochloric acid (Hcl) solution. The density of concentrated hydrochloric acid (37 % w/w) is 1.18 g/ml. how many milliliters of the concentrated acid would be required for the prescription?
Step 1: calculate the weight of the required quantity of the 3% Hcl solution:
a//// 3 %( w/v) =0.03 g/ml. ////a
a//// 0.03 g/ml x 120 ml =3.6 g. ////a
Step 2: calculate the volume of the required quantity of the 3% Hcl solution:
a//// 3.6 g/1.18 g/ml = 3.05 ml. ////a
a//// 3.6 g/1.18 g/ml = 3.05 ml. ////a
Step 3: calculate the volume of the 37% Hcl required for the prescription:
a//// 37%= 0.37. ////a
a//// 3.05 ml / 0.37= 8.24 ml of 37% Hcl, answer. ////a
a//// 37%= 0.37. ////a
a//// 3.05 ml / 0.37= 8.24 ml of 37% Hcl, answer. ////a
Dilution aliquots:
A pharmacist needs 0.015 ml of flavoring oil to prepare an oral liquid. Using alcohol as a solvent and a pipet accurate to 0.01 ml, how can this volume of flavoring oil be obtained?
Step 1: Select a multiple of the desired quantity that can be accurately measured with the pipet. For this example, use 10 as the multiple and measure 0.1 ml of flavoring oil (10 x 0.01ml).place the oil in a suitable graduated cylinder.
A pharmacist needs 0.015 ml of flavoring oil to prepare an oral liquid. Using alcohol as a solvent and a pipet accurate to 0.01 ml, how can this volume of flavoring oil be obtained?
Step 1: Select a multiple of the desired quantity that can be accurately measured with the pipet. For this example, use 10 as the multiple and measure 0.1 ml of flavoring oil (10 x 0.01ml).place the oil in a suitable graduated cylinder.
Step 2: dilute the quantity of flavoring oil calculated in step 1 with alcohol to a quantity of solution that is divisible by the selected multiple, for this ex. add sufficient alcohol to make 50ml of solution, mix well.
Step 3: calculate the aliquot of the sol that contains the desired quantity of flavoring oil a//// (0.015 ml) as follows: ////a
a//// 0.1ml/50ml=0.015ml/x. ////a
a//// X=7.5 ml aliquot, answer. . ////a
Step 3: calculate the aliquot of the sol that contains the desired quantity of flavoring oil a//// (0.015 ml) as follows: ////a
a//// 0.1ml/50ml=0.015ml/x. ////a
a//// X=7.5 ml aliquot, answer. . ////a
Step 4: remove 7.5 ml of the sol that contains the required 0.015 ml of the flavoring oil.
Solutions:
Solubility ratios in the literature and in the United States Pharmacopoeia 25/National Formulary 20 are given as “x:y” and “x in y” (e.g., 1:4 and 1 in 4). These expressions are stated as one part of solute plus four parts of solvent. The resulting product is described as a 1:5 solution; that is, the product contains one part of solute in 5 parts of solution.
Another ex.: a substance with a solubility of 1:3 contains 1 g of solute in 3 ml of solvent. The resulting product, a 1:4 solution, contains 1 part of solute in 4 parts of solution. In contrast, a 1:3 solution contains 1 g of solute in 3 ml of solution (i.e., sufficient solvent is added to make 3 ml of solution).
Solubility ratios in the literature and in the United States Pharmacopoeia 25/National Formulary 20 are given as “x:y” and “x in y” (e.g., 1:4 and 1 in 4). These expressions are stated as one part of solute plus four parts of solvent. The resulting product is described as a 1:5 solution; that is, the product contains one part of solute in 5 parts of solution.
Another ex.: a substance with a solubility of 1:3 contains 1 g of solute in 3 ml of solvent. The resulting product, a 1:4 solution, contains 1 part of solute in 4 parts of solution. In contrast, a 1:3 solution contains 1 g of solute in 3 ml of solution (i.e., sufficient solvent is added to make 3 ml of solution).