Parenteral Dosage of Drugs
Chapter 11
Calculation of Drug Dosage:
Parenteral
2
Calculation of Drug Dosage:
Parenteral
• Order
– Cleocin 150 mg IM every 12 hours
• Available
– Cleocin (clindamycin phosphate) 300 mg per
2 mL
3
Calculation of Drug Dosage:
Parenteral
• Step 1. Convert
– No conversion is necessary.
4
Calculation of Drug Dosage:
Parenteral
• Step 2. Think
– You want to give less than 2 mL
– Actually, you want to give 150 mg, which is
of 300 mg and 1 of 2 mL, or 1 mL
2
– Calculate to double-check your estimate.
1
2
5
Calculation of Drug Dosage:
Parenteral
• Step 3. Calculate
300 mg 150 mg

2 mL
X
300 X  300
X  1 mL
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Calculation of Drug Dosage:
Parenteral
• Given intramuscularly every 12 hours
• Select a 3 mL syringe
• Measure 1 mL of Cleocin 300 mg per 2 mL
7
Ratio-Proportion Method:
Parenteral with Conversion
• Order: Robinul 150 mcg IM
stat
• Supply: Robinul 0.2 mg per
mL
8
Ratio-Proportion Method:
Parenteral with Conversion
• Step 1. Convert
– Equivalent: 1 mg = 1,000 mcg
1,000 mcg
X

1 mg
0.2 mg
X  200 mcg
9
Ratio-Proportion Method:
Parenteral with Conversion
• Step 2. Think
– Give less than 1 mL but more than 0.5 mL
• Don’t be fooled into thinking 0.2 mg is less than
150 mcg
• 0.2 mg is more than 150 mcg
• 0.2 mg = 200 mcg
10
Ratio-Proportion Method:
Parenteral with Conversion
• Step 3. Calculate
200 mcg 150 mcg

1 mL
X
200 X
150
X  0.75 mL
11
Ratio-Proportion Method:
Parenteral with Conversion
• Given intramuscularly immediately
•
Select a 1 mL syringe
•
Measure 0.75 mL Robinul 0.2 mg per mL
•
You may have to change needles, as this
is an IM injection.
12
Guidelines for Syringe Selection
• Standard doses more than 1 mL
– Round to tenths and measure in a 3 mL
syringe
– 3 mL syringe is calibrated to 0.1 mL
increments
• 1.53 mL is rounded to 1.5 mL
• Drawn up in a 3 mL syringe
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Guidelines for Syringe Selection
• Small (less than 1 mL), critical care, or
children’s doses
– Round to hundredths and measure in 1 mL
syringe
– 1mL syringe is calibrated in 0.01 increments
• 0.257 mL is rounded to 0.26 mL
• Drawn up in a 1 mL syringe
14
Guidelines for Syringe Selection
• Amounts of 0.5 –1 mL calculated in tenths
• Can be accurately measured in either a 1 mL
or 3 mL syringe
15
Insulin Label
Manufacturer
Concentration
Type
Expiration Date
Brand Name
Storage
Species
Generic Name
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Combination Insulin Dosage
40 units
NPH
Units-100
insulin
12 units
Regular
Units -100 insulin
Total insulin dosage = 52 units
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Preparing Combination Insulin Dosage
1. Inject
30 units
of air.
2. Inject
10 units
of air.
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Preparing Combination Insulin Dosage
3. Withdraw
10 units
regular.
4. Withdraw
30 units
NPH for a
total of 40
units.
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Insulin Sliding Scale
• Order
– Humulin R Regular units-100 insulin subcut
based on glucose reading at 1600
20
Insulin Sliding Scale
*
Insulin Dose
Glucose Reading*
No coverage
Glucose less than 160
2 units
160–220
4 units
221–280
6 units
281–340
8 units
341–400
Glucose is greater than 400: Hold insulin; call MD stat.
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