NMC CBT Drug Calculations and Numeracy 2 — Questions and Answers
Question 1: A patient is prescribed 1.2 g of amoxicillin orally. The pharmacy supplies 500 mg capsules. How many capsules should be administered?
- 2 capsules
- 2.4 capsules — query the prescription (Correct answer)
- 3 capsules
- 1.2 capsules
Correct answer: 2.4 capsules — query the prescription
1.2 g = 1200 mg. 1200/500 = 2.4. Capsules cannot be divided, so query the prescription with the prescriber.
Convert: 1.2 x 1000 = 1200 mg. Formula: 1200/500 = 2.4. Since capsules cannot be halved, administering 2.4 is impossible. Don't round up (overdose) or down (underdose). Query the prescription — the prescriber may adjust to 1000 mg (2 capsules) or 1500 mg (3 capsules) or prescribe a different formulation.
Question 2: An IV infusion of 1 litre of 0.9% NaCl is prescribed over 8 hours. The giving set delivers 20 drops per mL. What is the drip rate?
- 42 drops/min (Correct answer)
- 25 drops/min
- 33 drops/min
- 50 drops/min
Correct answer: 42 drops/min
Drip rate = (1000 x 20) / (8 x 60) = 20000/480 = 41.67, rounded to 42 drops/min.
Step 1: 1 litre = 1000 mL. Step 2: 8 hours x 60 = 480 minutes. Step 3: (1000 x 20)/480 = 20000/480 = 41.67, rounded to 42 drops/min. Standard giving sets: 20 drops/mL for clear fluids, 15 drops/mL for blood.
Question 3: A child weighing 22 kg is prescribed paracetamol at 15 mg/kg. The oral suspension contains 250 mg in 5 mL. What volume should be administered?
- 5.6 mL
- 6.0 mL
- 6.6 mL (Correct answer)
- 7.2 mL
Correct answer: 6.6 mL
Dose = 15 x 22 = 330 mg. Volume = (330/250) x 5 = 6.6 mL.
Step 1: 15 mg/kg x 22 kg = 330 mg. Step 2: (330/250) x 5 = 1.32 x 5 = 6.6 mL. Always double-check paediatric calculations with a second registered nurse. Maximum daily dose: 60 mg/kg/day in divided doses, max 4 doses in 24 hours.
Question 4: A 70 kg patient requires dopamine at 5 mcg/kg/min. The bag contains 400 mg in 250 mL. What is the infusion rate in mL/hr?
- 10.2 mL/hr
- 13.1 mL/hr (Correct answer)
- 15.5 mL/hr
- 18.0 mL/hr
Correct answer: 13.1 mL/hr
Dose/min = 5 x 70 = 350 mcg. Dose/hr = 350 x 60 = 21000 mcg = 21 mg. Concentration = 400/250 = 1.6 mg/mL. Rate = 21/1.6 = 13.1 mL/hr.
Step 1: 5 mcg/kg/min x 70 kg = 350 mcg/min. Step 2: 350 x 60 = 21000 mcg/hr = 21 mg/hr. Step 3: 400 mg/250 mL = 1.6 mg/mL. Step 4: 21/1.6 = 13.125, rounded to 13.1 mL/hr. Must use an infusion pump. Independently verify with a second nurse.
Question 5: A prescription states: 'morphine 10 mg in 10 mL 0.9% NaCl IV, give 3 mg.' How many mL should be drawn up?
- 1 mL
- 3 mL (Correct answer)
- 5 mL
- 0.3 mL
Correct answer: 3 mL
Concentration = 10 mg/10 mL = 1 mg/mL. Volume = 3/1 = 3 mL.
Concentration: 10/10 = 1 mg/mL. Volume: 3 mg / 1 mg/mL = 3 mL. As a Schedule 2 controlled drug, two registered nurses must prepare and administer, the controlled drug register must be completed, and the remaining 7 mL disposed of per policy with a witness.
Question 6: A patient's fluid balance shows: IV NaCl 1000 mL, oral 350 mL, IV antibiotics 100 mL x 3 doses. Output: urine 1100 mL, vomit 200 mL. What is the fluid balance?
- +350 mL (Correct answer)
- +250 mL
- +450 mL
- +150 mL
Correct answer: +350 mL
Intake = 1000 + 350 + 300 = 1650 mL. Output = 1100 + 200 = 1300 mL. Balance = +350 mL.
Total intake: 1000 + 350 + (100 x 3) = 1650 mL. Total output: 1100 + 200 = 1300 mL. Balance: 1650 - 1300 = +350 mL (positive). Insensible losses (~500-800 mL/day) are not typically included in ward fluid balance charts but should be considered clinically.
NMC CBT Drug Calculations and Numeracy 2
A patient is prescribed 1.2 g of amoxicillin orally.
The pharmacy supplies 500 mg capsules.
How many capsules should be administered?