Pharmacy technician math practice: cram pack

Formula sheets, the key method steps for every topic and 8 practice problems, with full solutions at the back.

New problemsBack to the course

In the print window, choose “Save as PDF” to keep a copy on your device.

1Formulas and methods

Pharmacy calculations

Percentage strength
% w/v = g per 100 mL
Amount in a solution
g = % × mL / 100
Ratio strength
1:X = 1 g in X mL; % = 100 / X
Reconstitution
final volume = diluent + powder volume
Concentration
mg/mL = drug in vial / final volume
Alligation
parts of H = T − L, parts of L = H − T
Water or base
0%

Dosage calculations

Dose from strength
volume = dose / strength
Weight-based dose
dose = mg/kg × body weight
Tablets
number = dose / tablet strength
Units
1 g = 1000 mg, 1 mg = 1000 mcg

Method

  1. Convert the ordered dose and the stock strength to the same unit.
  2. Use desired over have times quantity: (D/H) × Q.
  3. For weight-based doses, multiply by the weight in kg first, then divide the daily dose by the number of doses.
  4. Estimate first and check that the answer is reasonable.

IV infusion rates

Pump rate
mL/h = volume (mL)/time (h)
Drip rate
drops/min = volume (mL) × drop factor / time (min)
Infusion time
time (h) = volume (mL)/rate (mL/h)

Method

  1. Pump rate in mL/h: volume divided by time in hours.
  2. Drip rate in drops/min: volume × drop factor divided by time in minutes.
  3. For time remaining: volume left divided by the rate.
  4. Round as the question or the equipment requires.

Pediatric & critical-care dosing

Daily dose
mg/day = mg/kg/day × weight (kg)
Doses per day
number = 24 h / dosing interval (h)
Pounds to kilograms
kg = lb / 2.2
Infusion concentration
units/mL = units in bag / bag volume
Pump rate
mL/h = dose per hour / concentration
Titrated drip
mL/h = mcg/kg/min × kg × 60 / (mcg/mL)
Dose from pump rate
mcg/kg/min = mL/h × (mcg/mL) / (60 × kg)
Units
1 mg = 1000 mcg

2Practice problems

1.Pharmacy calculationsMedium
cefuroxime 750 mgAdd 7.2 mL sterile water.Powder volume: 0.3 mL.450 mg → ? mL

Practice exercise (made-up values, not clinical guidance). A vial contains cefuroxime 750 mg as a powder. The practice label says to add 7.2 mL of sterile water; the powder adds 0.3 mL to the volume. The prescribed dose is 450 mg. What volume V do you draw up? Round to one decimal place.

750 mg7.2 mL+0.3 mL450 mg
V = mL
2.Pharmacy calculationsHard
0123455 mL

A vial holds 500 mg of powder. You add 3.4 mL of diluent, and the powder adds 0.6 mL of volume. The prescription is 475 mg. Draw up the dose: what volume V do you give?

500 mg3.4 mL + 0.6 mL475 mg
V = mL
3.Dosage calculationsMedium
22 kg15 mg/kg/day4× per dayD = ? mg

A patient weighs 22 kg. The prescribed dose is 15 mg/kg per day, given in 4 equal doses. How many milligrams D are given per dose?

22 kg15 mg/kg/day4× per day
D = mg
4.Dosage calculationsHard
00.10.20.30.40.50.60.70.80.911 mL

The prescription is 520 units of a drug that comes as 1000 units/mL. Draw up the dose in the 1 mL syringe: what volume V do you give?

520 units1000 units/mL
V = mL
5.IV infusion ratesMedium
1180 mLleft? mL/h5 h left

1500 mL was ordered over 8 hours. After 3 hours you find that 1180 mL is still in the bag, and the order must still finish on time. To what rate R in mL/h must the pump be reset?

1500 mL / 8 hafter 3 h: 1180 mL
R = mL/h
6.IV infusion ratesHard
500 mg250 mL25 mL/h? mg/h

A bag contains 500 mg of a drug in 250 mL and runs at 25 mL/h. How many milligrams per hour D does the patient receive?

500 mg/250 mL25 mL/h
D = mg/h
7.Pediatric & critical-care dosingMedium
heparin 1 000 units/mL60 units/kg · 56 kg → V = ? mL

Practice exercise (made-up values, not clinical guidance). A practice protocol calls for a heparin bolus of 60 units/kg for a patient who weighs 56 kg. The vial contains 1 000 units/mL. What volume V do you draw up? Round to one decimal place.

60 units/kg56 kg1 000 units/mL
V = mL
8.Pediatric & critical-care dosingHard
8 mg250 mLnorepinephrine? mL/h66 kg12 mcg/min

Practice exercise (made-up values, not clinical guidance). A patient who weighs 66 kg has an order for norepinephrine at 12 mcg/min. The bag contains 8 mg in 250 mL. Find the pump rate R in mL/h. Round to one decimal place.

8 mg/250 mL12 mcg/min66 kg
R = mL/h

3Solutions

1.Pharmacy calculations

Answer: V = 4.5 mL

Reconstitution: the powder takes up space, so the final volume is the diluent plus the powder volume. Concentration = drug in the vial/final volume, and the volume to give = dose/concentration. On a multi-strength label, use the concentration that belongs to the amount of diluent you actually added. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Final volume

7.2 + 0.3 = 7.5 mL

Concentration

750/7.5 = 100 mg/mL

Volume to give

V = 450/100 = 4.5 mL

Answer

V = 4.5 mL
2.Pharmacy calculations

Answer: V = 3.8 mL

Strength to volume: turn the strength into mg per mL first. A w/v percentage is grams per 100 mL, so x% = 10x mg/mL. A ratio strength 1:n is 1 g in n mL. After reconstitution the concentration is the powder's dose over the final volume (diluent + powder volume). Then volume = dose/concentration.

Final volume and concentration

3.4 + 0.6 = 4 mL
C = 500/4 = 125 mg/mL

Volume

V = 475/125 = 3.8 mL

Answer

V = 3.8 mL
3.Dosage calculations

Answer: D = 82.5 mg

Dose calculation: the amount to give equals what is prescribed divided by what you have, times the quantity it comes in: amount = (desired dose/stock strength) × stock volume. Always keep the units the same (convert g to mg, mg to mcg first) and check that the answer is sensible.

Total per day

15·22 = 330 mg

Per dose

D = 330/4 = 82.5 mg

Answer

D = 82.5 mg
4.Dosage calculations

Answer: V = 0.52 mL

Drawing up a dose: volume = (prescribed dose/stock strength) × stock volume. Convert to the same units first, then check that the volume fits the syringe and lands on one of its graduations.

Volume

V = 520/1000 = 0.52 mL

On the syringe

On this 1 mL syringe every small line is 0.01 mL.

Answer

V = 0.52 mL
5.IV infusion rates

Answer: R = 236 mL/h

Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.

Original rate

1500/8 = 187.5 mL/h

New rate

R = 1180/5 = 236 mL/h

Answer

R = 236 mL/h

This is more than a 25% increase: most hospitals require you to contact the prescriber instead of catching up, and to assess the patient for fluid overload.

6.IV infusion rates

Answer: D = 50 mg/h

Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.

Concentration

500/250 = 2 mg/mL

Dose rate

D = 2·25 = 50 mg/h

Answer

D = 50 mg/h
7.Pediatric & critical-care dosing

Answer: V = 3.4 mL

Heparin and insulin infusions: concentration = units in the bag/bag volume (units/mL). Pump rate (mL/h) = units per hour/concentration, and units per hour = mL/h × concentration. For a weight-based order, units/h = units/kg/h × weight first. A bolus volume = units needed/vial strength. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Units needed

60·56 = 3 360 units

Volume

V = 3360/1000 = 3.36 ≈ 3.4 mL

Answer

V = 3.4 mL
8.Pediatric & critical-care dosing

Answer: R = 22.5 mL/h

Titrated drips: first find the concentration in mcg/mL (mg × 1000/mL). For a weight-based order, mcg/min = mcg/kg/min × weight. Then mL/h = mcg/min × 60/concentration. Working backwards, mcg/kg/min = mL/h × concentration/(60 × weight). The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Concentration

8 000/250 = 32 mcg/mL

Dose per hour

The order is per minute for the whole patient, so the weight is not needed.

12·60 = 720 mcg/h

Pump rate

R = 720/32 = 22.5 mL/h

Answer

R = 22.5 mL/h

This is independent practice material. ExamProblems is not affiliated with or endorsed by the organisation that runs this exam, and the exam name is used only to describe the content. The PTCE is run by the Pharmacy Technician Certification Board (PTCB), which is not affiliated with ExamProblems and does not endorse it.

ExamProblems · examproblems.com/courses/pharmacy-technician-math