Unit 39: Dosage Calculations

A prescription reads: Amoxicillin 0.5 g po tid. Capsules available: 250 mg.
How many capsules per dose?

A. 1
B. 2
C. 3
D. 6

B. 2
0.5 g = 500 mg → 500 ÷ 250 = 2 capsules per dose

A patient is prescribed 500 mg qid. Tablets available: 250 mg.
How many tablets per day?

A. 4
B. 6
C. 8
D. 16

C. 8
500 mg per dose → 2 tablets × 4 doses = 8 tablets/day

Cleocin 150 mg IM q12h x 4 days. Available: 100 mg/2 mL.
Total volume needed?

A. 12 mL
B. 18 mL
C. 24 mL
D. 30 mL

C. 24 mL
300 mg/day × 4 = 1200 mg → (100 mg = 2 mL) → 1200 mg = 24 mL

Order: iii tsp po tid x 7 days
How many mL total?

A. 105 mL
B. 210 mL
C. 315 mL
D. 630 mL

C. 315 mL
3 tsp = 15 mL → 15 × 3 = 45 mL/day → × 7 = 315 mL

A patient weighs 220 lb. Dose: 2 mg/kg.
What is the dose?

A. 100 mg
B. 150 mg
C. 200 mg
D. 250 mg

C. 200 mg
220 ÷ 2.2 = 100 kg → 100 × 2 = 200 mg

A drug is dosed at 0.4 mg per 4 kg. Patient weighs 88 kg.
Dose?

A. 4 mg
B. 6 mg
C. 8.8 mg
D. 12 mg

C. 8.8 mg
88 ÷ 4 = 22 → 22 × 0.4 = 8.8 mg

Prepare 360 mL of 250 mg/5 mL solution. Tablets: 200 mg.
How many tablets?

A. 72
B. 80
C. 90
D. 100

C. 90
360 ÷ 5 = 72 doses → 72 × 250 = 18,000 mg → ÷ 200 = 90

Order: 750 mg. Available: 250 mg/5 mL.
How many mL?

A. 10 mL
B. 12 mL
C. 15 mL
D. 20 mL

C. 15 mL
750 ÷ 250 = 3 → 3 × 5 mL = 15 mL

Order: 1 g. Available: 500 mg tablets.
How many tablets?

A. 1
B. 2
C. 3
D. 5

B. 2
1 g = 1000 mg → 1000 ÷ 500 = 2

Order: 0.25 g. Available: 125 mg tablets.
How many tablets?

A. 1
B. 2
C. 3
D. 4

B. 2
0.25 g = 250 mg → 250 ÷ 125 = 2

How many mL in 3 tbsp?

A. 15 mL
B. 30 mL
C. 45 mL
D. 60 mL

C. 45 mL
1 tbsp = 15 mL → 3 × 15 = 45

How many mL in 4 tsp?

A. 10 mL
B. 15 mL
C. 20 mL
D. 25 mL

C. 20 mL
1 tsp = 5 mL → 4 × 5 = 20

Convert 2.5 g to mg:

A. 250 mg
B. 2500 mg
C. 25,000 mg
D. 0.25 mg

B. 2500 mg

Convert 500 mg to g:

A. 0.05 g
B. 0.5 g
C. 5 g
D. 50 g

B. 0.5 g

Convert 110 lb to kg:

A. 40 kg
B. 45 kg
C. 50 kg
D. 55 kg

C. 50 kg
110 ÷ 2.2 = 50

Order: 250 mg q6h. Available: 125 mg tablets.
How many tablets per day?

A. 4
B. 6
C. 8
D. 12

C. 8
250 mg = 2 tablets → q6h = 4 doses → 2 × 4 = 8

Order: 5 mL tid x 10 days
Total volume?

A. 100 mL
B. 120 mL
C. 150 mL
D. 200 mL

C. 150 mL
5 × 3 = 15 mL/day → × 10 = 150

Order: 400 mg/day. Available: 200 mg tablets.
Days supply for 20 tablets?

A. 5
B. 10
C. 20
D. 40

B. 10
400 mg/day = 2 tabs/day → 20 ÷ 2 = 10 days

Order: 2 mg/kg. Patient: 154 lb.
Dose?

A. 100 mg
B. 120 mg
C. 140 mg
D. 160 mg

C. 140 mg
154 ÷ 2.2 = 70 kg → 70 × 2 = 140

Order: 100 mg/5 mL. Patient needs 300 mg.
Volume?

A. 10 mL
B. 15 mL
C. 20 mL
D. 25 mL

B. 15 mL
300 ÷ 100 = 3 → 3 × 5 = 15

Order: 0.75 g. Available: 250 mg tablets.
How many tablets?

A. 2
B. 3
C. 4
D. 5

B. 3
0.75 g = 750 mg → ÷ 250 = 3

Order: 10 mL bid x 5 days
Total volume?

A. 50 mL
B. 75 mL
C. 100 mL
D. 150 mL

C. 100 mL
10 × 2 = 20/day → × 5 = 100

Order: 500 mg q8h. Available: 250 mg capsules.
Capsules per day?

A. 3
B. 4
C. 6
D. 8

C. 6
500 mg = 2 caps → 3 doses → 6 caps

Order: 1 tsp qid x 7 days
Total mL?

A. 70
B. 105
C. 140
D. 175

C. 140
5 × 4 = 20/day → × 7 = 140

Order: 250 mg/5 mL. Patient takes 500 mg per dose.
Volume per dose?

A. 5 mL
B. 10 mL
C. 15 mL
D. 20 mL

B. 10 mL

Order: 0.3 g. Available: 150 mg tablets.
How many tablets?

A. 1
B. 2
C. 3
D. 4

B. 2
0.3 g = 300 mg → 300 ÷ 150 = 2

Patient weighs 132 lb. Dose: 1 mg/kg.
What dose?

A. 50 mg
B. 60 mg
C. 70 mg
D. 80 mg

B. 60 mg
132 ÷ 2.2 = 60 kg → 60 × 1 = 60 mg

Order: 250 mg q6h. Available: 125 mg tablets.
How many tablets per day?

A. 4
B. 6
C. 8
D. 10

C. 8
250 mg = 2 tabs → 4 doses/day → 2 × 4 = 8

Order: 2 tsp tid x 5 days
Total mL?

A. 100 mL
B. 150 mL
C. 200 mL
D. 250 mL

B. 150 mL
2 tsp = 10 mL → 10 × 3 = 30/day → × 5 = 150

Order: iii tsp po bid x 10 days
Bottle concentration: 250 mg/5 mL
How much volume is dispensed?

A. 150 mL
B. 200 mL
C. 300 mL
D. 600 mL

C. 300 mL
3 tsp = 15 mL → 15 × 2 = 30/day → × 10 = 300
(Concentration irrelevant)

Dose: 0.5 mg per 5 kg. Patient = 50 kg
Dose?

A. 2.5 mg
B. 5 mg
C. 10 mg
D. 25 mg

B. 5 mg
50 ÷ 5 = 10 → 10 × 0.5 = 5 mg

Available: 200 mg/5 mL
Order: 400 mg
How many mL?

A. 5 mL
B. 10 mL
C. 15 mL
D. 20 mL

B. 10 mL
400 ÷ 200 = 2 → 2 × 5 = 10

Prepare 120 mL of 100 mg/5 mL solution
Total mg needed?

A. 1200 mg
B. 2400 mg
C. 3000 mg
D. 6000 mg

B. 2400 mg
120 ÷ 5 = 24 doses → 24 × 100 = 2400

Need 2400 mg total. Tablets: 300 mg each
How many tablets?

A. 6
B. 8
C. 10
D. 12

B. 8
2400 ÷ 300 = 8

Calculated dose = 8.6 mg
Round to nearest whole number:

A. 8 mg
B. 9 mg
C. 10 mg
D. 8.5 mg

B. 9 mg

Order: q8h dosing
How many doses/day?

A. 2
B. 3
C. 4
D. 6

B. 3

Order: q12h
How many doses/day?

A. 1
B. 2
C. 3
D. 4

B. 2

Convert 0.05 g to mg:

A. 5 mg
B. 50 mg
C. 500 mg
D. 5000 mg

B. 50 mg

Convert 176 lb to kg:

A. 60 kg
B. 70 kg
C. 80 kg
D. 90 kg

C. 80 kg

Order: 500 mg tid x 7 days
Tablets: 250 mg
Total tablets?

A. 21
B. 28
C. 35
D. 42

D. 42
500 mg = 2 tabs → 3/day = 6 tabs/day → × 7 = 42

Order: 1 tbsp qid x 5 days
Total mL?

A. 200
B. 250
C. 300
D. 350

C. 300
1 tbsp = 15 mL → 15 × 4 = 60/day → × 5 = 300

Dose: 2 mg/kg. Patient: 99 lb
Dose?

A. 80 mg
B. 90 mg
C. 100 mg
D. 110 mg

B. 90 mg
99 ÷ 2.2 = 45 kg → 45 × 2 = 90

Order: 250 mg qid
Available: 125 mg tablets
Tabs per dose?

A. 1
B. 2
C. 3
D. 4

B. 2

Order: 15 mL bid x 7 days
Total volume?

A. 150
B. 180
C. 210
D. 240

C. 210
15 × 2 = 30/day → × 7 = 210

Order: 0.5 g tid x 5 days
Tablets: 250 mg
Total tablets?

A. 15
B. 20
C. 30
D. 40

C. 30
0.5 g = 500 mg → 2 tabs/dose
2 × 3 = 6/day → × 5 = 30