1. Ch 20: Systems of Measurement
Three Systems
Avoirdupois (household system)
Metric
Apothecary (rarely used) ©

2. Metric System Conversion Factors: Micro – one millionth
Milli – one thousandth
Centi – one hundredth
Deci – one tenth
Kilo – one thousand ©

3. Metric System Metrics are expressed in the form of decimals
1000mcg = 1mg
1000mg = 1g
1000g = 1kg
1000ml = 1L
Metrics are expressed in the form of decimals
ie.) 300ml = 0.3L ©

4. Avoirdupois System
Conversion Factors: 3 tsp = 1 tbsp 2 tbsp = 1 oz 16 oz = 1 pt 2 pt = 1 qt 4 qt = 1 G 16oz = 1 lb ©

5. Conversion Factors Between Systems
1 tsp = 5 ml 1 tbsp = 15 ml 1 oz = 30 ml (29.57ml) 1 pt = 480 ml (473ml) 1 G = 3840 ml (3784ml)
1 g = 15.4 gr 1 gr = 60 mg (64.8mg) 1 kg = 2.2 lb 1 lb = 454 g 1 oz = 30 g (28.35g)
Why are there 2 values listed for some conversions?
The values listed in the parentheses are the exact values for the conversion. The other is an approximation. It is acceptable to use the approximation when calculating amounts to be dispensed, but always use the exact values when performing compounding calculations.
YOU SHOULD KNOW BOTH! ©

6. Class 4 Slides Pharmacy Math Continues…….
Ch 21: Conversions
Pharmacy Math Continues……. ©
copyright Mark Greenwald - all rights reserved

7. Remember Always set up your units first
Be sure the unwanted units cancel and you are left with the appropriate answer
Then plug in your values and calculate the answer ©

8. Conversions X X 2.3 oz = ? ml 2.3 oz 30ml x = 69 ml 1 oz
Arrange the units so they will cancel and solve
Value x Conversion Factor = Answer
2.3 oz ml X
x = 69 ml
1 oz X
The units of ounces cancel, and you are left with milliliters ©

9. Conversions X X X X 1.3 kg = ? grams 1.3 kg 2.2 lb 454g x x = 1,298g
Value x Conversion Factor x Conversion Factor = Answer
1.3 kg lb g X X
x x = 1,298g
1 kg lb X X ©

10. Try This One
2 kg = ? ounces ©

11. Conversions 2 kg = ? ounces 2 kg 2.2 lb 454g 1 oz 1 kg 1 lb 30g X X X
x x x = 67oz
1 kg lb g X X X ©

12. One More for the Road
60 oz = ? Liters ©

13. One More for the Road 60 oz = ? liters X X X X 60oz 30ml 1 L
x x = 1.8 L
1 oz ml X X ©

14. CH 22: Methods of Measurement
Whenever we measure something, we have an inherent ‘Margin of Error” produced
No measurement can be 100% accurate
What we strive to do is minimize this potential for error ©

15. How Can We Minimize the Margin of Error?
Use the appropriate type of measuring equipment
Use the appropriate size of equipment
Let’s discuss correct Methods of
Measurement…. ©

16. Measurement of Solids Small Samples Large Samples
The pharmacy torsion balance
Large Samples
The pharmacy scale ©

17. The Torsion Balance Very accurate Measures Small Amounts of Material
6 mg to 120 g
Used with pharmacy weight set ©

18. Use of the Torsion Balance
Clean pans
Use weighing papers to avoid sample contact with the pan
Level the balance (zero the balance)
Place sample in center of left pan
Weights in center of right pan ©

19. The Pharmacy Scale For larger samples May be electronic or mechanical
Always be sure to level the scale before use ©

20. Measurement of Liquids
Small Volumes
- Syringe or pipettes
Larger Volumes
- Graduated Cylinder
Use at Home
- Measuring spoon
- Oral syringe
- Medicine cup ©

21. The Graduated Cylinder
Comes in various sizes (15ml – 500ml)
Comes in glass or plastic
Labeled in milliliters and ounces
BEWARE OF THE MENISCUS! ©

22. The Meniscus Phenomenon
Occurs only with a glass graduate
When the light passes through the glass walls of the graduate, a bending of the light occurs causing the surface of the liquid to appear curved.
In order to accurately read the volume, you must read the level of the liquid from the lowest point of the curve
Read at the bottom of the meniscus ©

23. The Syringe Comes in various sizes (0.5ml-50ml)
Comes with different types of needle attachments
Available with needle attached or separate
Available as an oral syringe with no needle (needles will not fit)
Parenteral syringes are in sterile packaging ©

24. Syringes May have different tips depending on their intended use
Luer-Lok tip is a Becton-Dickinson design that locks the needle on the syringe with a twisting motion ©

25. How to Read the Volume in a Syringe
Always read the volume at the black ring closest to the tip of the syringe ©

26. Ch 23: Pharmacy Math - Proportions
Class 4 Slides
Ch 23: Pharmacy Math - Proportions
Proportions will be your most used pharmacy calculation
Used when two expressions are directly related to one another
For instance, if 1 kg of drug cost us $5, how much will 2 kg cost?
both expressions contain cost per weight
if they are set up as ratios, once the problem is solved, both ratios should be equal ©
copyright Mark Greenwald - all rights reserved

27. Proportions If a drug costs us $5 per kg, how much will 2kg cost us?
What unit do we know BOTH values for?
Kilograms – so that goes in the denominator ©

28. Proportions Which expression do we know both values for?
$5 per 1 kilogram
So the expression on the left will be
$5 / 1kg
And the right expression is the unknown with kilograms in the denominator
$5 / 1kg = x / 2 kg ©

29. Proportions $5.00 x 10 = = $10 1kg 2kg 1kg Now we solve the equation:
= = $10
1kg 2kg 1kg ©

30. More Examples
A formula calls for 42 capsules of 300mg of drug. How many milligrams would be required to make 24 capsules? ©

31. More Examples 300mg x 7,200 = = 171.4 mg 42 caps 24 caps 42
A formula calls for 42 capsules of 300mg of drug. How many milligrams would be required to make 24 capsules?
300mg x ,200
= = mg
42 caps caps 42 ©

32. More Examples
If 12 g of powder occupies 7ml of volume, how many milliliters will 150g occupy? ©

33. More Examples 7ml x 1,050 = = 87.5 ml 12g 150g 12
If 12 g of powder occupies 7ml of volume, How many milliliters will 150g occupy?
7ml x 1,050
= = ml
12g 150g 12 ©

34. More Examples
If a chemical costs $14.00 per kg, how many kilograms could $ buy? ©

35. More Examples 1kg x 128 = = 9.14 kg $14 $128 14
If a chemical costs $14.00 per kg, how many kilograms could $ buy?
1kg x 128
= = kg
$14 $128 14 ©

36. More Examples
500 Penicillin tablets cost $ What would be the cost for 48 tablets? ©

37. More Examples $43.09 x 2,068.32 = = $4.14 500tabs 48tabs 500
500 Penicillin tablets cost $ What would be the cost for 48 tablets?
$ x ,068.32
= = $4.14
500tabs 48tabs 500 ©

38. One Last Example
Five pieces of Bazooka bubble gum cost $0.58. How much would 39 pieces cost? ©

39. One Last Example $0.58 x 2.62 = = $4.52 5 pcs 39 pcs 5
Five pieces of Bazooka bubble gum cost $0.58. How much would 39 pieces cost?
$ x
= = $4.52
5 pcs pcs ©