The document discusses various methods for calculating medication dosages using ratios, proportions, conversions between measurement systems, and calculations based on weight. It provides examples of calculating dosage amounts from given concentrations in vials or syringes. It also addresses calculations for intravenous infusions and piggyback infusions, including drip rates and time required.

1. Basic Computation/s
Part II
IV Drugs & IVF
Chapter 4

2. Interpretation/Calculating
Medication Dosages
 Ratio – is the relationship of two
quantities
 1:10 , 1:2500
 1/10 , 1/2500

3. Interpretation/Calculating
Medication Dosages
 RATIO
 e.g For every 20 students there is 1
teacher. The ratio of teacher to
students is 1 in 20 or 1:20 or 1/20

4.  Proportion – formed by using two ratios
that are equal
 1 = 5 = 2 x 5 = 10 x 1
2 10
 Cross products are equal to

10 = 10
 ½ is equal to 5/10
Interpretation/Calculating
Medication Dosages

5. Proportion
 Dose ¼ = 3/12
 Cross products are 12 = 12
 ¼ = 3/12

6. Example:
 The Md orders 20 mg IM of a drug for a
patient. The drug is available in 10 ml vial
that contains 50 mg of drug. How many ml
will be needed to supply the dose of 20 mg?
Given:
 1. 10 ml vial
 2. 50 mg of drug in 10 ml vial
 3. 20 mg is the desired

7. Cont.
 Ratio 10ml = 1ml
 50mg 5mg
 Ratio for the required dose x ml
20 mg
Proportion: 1ml = x ml
5mg 20 mg
 5 x x = 1 x 20
 5x = 20
 x = 4ml ( 20 divided by 5 )

8. Example/s:.
1. Ampicillin oral susp. 250mg/5ml . How
many ml would be measured into a
medication syringe to obtain a dose of
75mg of ampicillin?

9. Example/s
 2. Paracetamol 125mg/ 5ml. How many
ml would be measured into a
medication syringe to obtain 15 mg of
Paracetamol?

10. Example/s
 3. How many ml of Paracetamol IV
should be given to obtain a dose of
15mg in a 15kg-man, if a vial contains
300mg/2ml of Paracetamol?

11. Example/s
 4. A vial contains 250mg of tetracycline
HCl in a total of 2 ml of solution. How
many mg of tetracycline HCl are
contained in 0.6 ml of this solution?

12. Conversion Between
Systems of measurement
 1000 g = 1 kg
 1000 mg = 1 g
 1000 ng = 1 mcg
 1000 ml = 1 L
 100 ml = 1 dL

13. Conversion Between
Systems of measurement
 Rule: 1
 To convert a quantity in the metric
system to a large metric unit (mg to g)
move the decimal point to the left
 Smaller to larger =right to left
 Example: 2mg = 0.002g

14. Conversion Between
Systems of measurement
 Rule: 2
 To convert a quantity to a smaller metric
unit, move the decimal point to the right
 Example: 2.4 l = 2400 ml

15. Examples
 Convert 25 g to mg
 Convert 150 ml to liters

16. Apothecary System of
weights
 based upon the grain, which is the
smallest unit in the system
 Nitroglycerin 1/100gr, 1/150 gr
 Atropine sulfate 1/200gr. 1/150 gr
 Approximate equivalent

15 grains = 1 gram

1grain = 60 mg

17. Apothecary System of
weights
 Convert 15 milligrams to grains
 1 grain = x grain
60 mg 15 mg
60 x = 15
 x = 15/60
 x = .25 grain

18. Example:
The physician orders 7 ½ grains of
aminophylline po for a client. On hand are
aminophylline tablets 500 mg. How many
tablets are required for one dose?
GIVEN:
 1 gram = x gram
15 grain 7.5 grain
 15 x = 7.5
 x = 0.5 g (500mg)

19. Example:
 How many mg of nitroglycerin are in
one 1/150 grain tablet of the drug?
 Given:
 1 gram = x gram
 15 grains 1/150 grains
 15 x = 1/150 = .0067
 x = 0.0004g = 0.4 mg

20. Calculation of Fractional
Doses:
 ratio and proportion

21. Example:
The Md orders 1,000,000 units of Pen G for a
patient. The pen G on hand is available as a
solution containing 250,000 units/ml
 250,000 units = 1, 000,000 units
1 ml x ml
 250,000x = 1,000,000
 x = 4 ml

22. Example 1:
 The physician orders 250 mcg of
Vitamin B12 IM daily. The vitamin on
hand is labeled 1,000mcg/ml. How
many ml should be given to the patient?

23. Example 2:
 A patient is to be given 25 mg
Diphenhydramine po and is available as
12.5mg/5ml prep.. How many ml
should be given?

24. Example 3:
 A medication order calls for 750 mg
calcium lactate to be given TID PO. On
hand are tablets of calcium lactate 0.5
g. How many tablets should be given
for each dose?

25. Calculation of Dosages
Based on Weight
 The physician orders thiabendazole
chewable tablets for a 110 pound child.
The recommended dosage is 20
mg/kg/dose. How many 500 mg tablets
should be given to this patient for each
dose.

26. Calculation of Dosages
Based on Weight
 Convert weight to kg
 20 mg = x mg
 1 kg 50 kg
 x = 1000 mg
 500 mg = 1000mg
 1 tab x tab
 x = 2 tablets per dose

27. Example:
 The recommended dose of Meperidine
is 6mg/kg/day for pain. It is given every
4 to 6 hours. How many ml of Demerol
injection 50mg/ml should be
administered to a 33 pound child as a
single dose every 6 hours?

28. Cont.
 Calculate the daily dose for a 33-pound
child
 6mg/ 1 kg (2.2lb) = x mg / 33 lb
 x = 90 mg Demerol / day

29. Cont.
 Calculate the number of ml of demerol
injection 50 mg/ml needed for the daily
dose
 50 mg/ 1 ml = 90 mg/ x ml

30. Cont.
 Calculate the number of ml to be given
every 6 hours
 1.8 ml/ 24 h = x ml/ 6 h
 24 x = 10.8
 x = 0.45 ml

31. Calculations Involving
Intravenous Administration
 How long will it take to complete an IV
infusion of 1.5 L of D5 W being
administered at the rate of 45 drops
/min? The IV set is calibrated to deliver
15 drops/ml.

32. Calculations Involving
Intravenous Administration
 Determine the number of ml/min being
infused
 Drop rate of IV set =
 15 gtt/1ml = 45gtt/ x ml

15 x = 45

x = 3 ml/min

33. Calculations Involving
Intravenous Administration
Calculate the number of ml/hour
3 ml/min. x 60 min/hr = 180/ hour

34. Calculations Involving
Intravenous Administration
 Calculate the number of hours required to
administer the total volume of the
solution. If 180 ml are delivered each
hour, then how many hours are required
to administer 1,500 ml?
 180ml/hr = 1,500 ml/hr
 180 x = 1,500
 x = 8.3 hours or 8 hours 20 min.

35. Calculations Involving Piggyback
IV Infusion
 An IV piggyback of Cefazolin 500mg in
100ml/hour is ordered. The piggyback
IV set is calibrated to deliver 10 gtts.ml.
How many drops/min. should be
administered?

36. Calculations Involving
Piggyback IV Infusion
 100 ml/ 60 min. = x ml/ min.
 60 x = 100
 x = 1.7 ml/ min.
 Flow rate:
 Drop rate
 10 gtt/ min./ 1min. = x gtt/ 1.7 ml
 X = 17 gtt/ min.

37. Calculations Involving
Piggyback IV Infusion
 Daily fluid requirement
 2000ml of electrolyte solution
administered 24 hours and that
Cefazolin sodium 500 mg in 100 ml/hr is
ordered QID. The number od ml/day
and the times of the piggybank infusion
must be subtracted from the daily fluid
requirement.