Saunders NCLEX-RN Dosage Calculation Test Bank | 2025 Comprehensive Nursing Math Practice | mg/kg, IV Flow Rates, Reconstitution & Safety-Based Rationales

Saunders Comprehensive Review for the NCLEX-PN®
Examination
9th Edition
• Author(s)Linda Anne Silvestri; Angela Silvestri


TEST BANK


Question 1 — Dosage by weight (mg/kg)
An order reads: Ceftriaxone 50 mg/kg IV for a child who weighs
22 lb. The vial on hand contains 250 mg/5 mL. How many mL
will you administer for one dose? (Round to the nearest tenth.)
Solution (step-by-step):
1. Convert weight to kg: 22 lb÷2.2=10.0 kg22\ \text{lb} \div
2.2 = 10.0\ \text{kg}22 lb÷2.2=10.0 kg.
2. Calculate ordered dose in mg:
50 mg/kg×10.0 kg=500 mg50\ \text{mg/kg} \times 10.0\
\text{kg} = 500\ \text{mg}50 mg/kg×10.0 kg=500 mg.
3. Use dimensional analysis to find mL: label has
250 mg/5 mL250\ \text{mg} / 5\ \text{mL}250 mg/5 mL.
mL=500 mg×5 mL250 mg=500×5250=10.0 mL.\text{mL} = 500\
\text{mg} \times \dfrac{5\ \text{mL}}{250\ \text{mg}} = 500

,\times \dfrac{5}{250} = 10.0\
\text{mL}.mL=500 mg×250 mg5 mL=500×2505=10.0 mL.
4. Round: already 10.0 mL → 10.0 mL.
Rationale (correct vs common incorrect answers):
• Correct: conversion to kg and dimensional analysis
preserve units and avoid decimal misplacement.
• Common errors: forgetting to convert lb → kg (would give
1/10th the dose), or dividing mg by mL instead of using the
ratio. Saunders emphasizes dimensional analysis and
verifying weight units before calculation. Elsevier Health


Question 2 — Dosage by weight (mg/kg)
Order: Gentamicin 2 mg/kg IV single dose. Patient weight: 88
kg. Available vial: 80 mg/2 mL. How many mL will you
administer? (Round to nearest tenth.)
Solution:
1. Dose required: 2 mg/kg×88 kg=176 mg2\ \text{mg/kg}
\times 88\ \text{kg} = 176\
\text{mg}2 mg/kg×88 kg=176 mg.
2. Label: 80 mg/2 mL=40 mg/mL80\ \text{mg} / 2\ \text{mL}
= 40\ \text{mg/mL}80 mg/2 mL=40 mg/mL.
3. mL = 176 mg÷40 mg/mL=4.4 mL176\ \text{mg} \div 40\
\text{mg/mL} = 4.4\ \text{mL}176 mg÷40 mg/mL=4.4 mL.

, 4. 4.4 mL.
Rationale:
• Correct: convert vial concentration to mg/mL or use ratio
directly.
• Common mistake: using 80 mg per 2 mL as mg ÷ 2 instead
of calculating mg/mL leading to wrong decimal. Always
show unit cancellation.


Question 3 — IV flow rate (mL/hr)
Order: D5W 1,000 mL over 8 hours. Set the infusion using an
electronic pump. What rate (mL/hr) do you program? (Round to
nearest whole number.)
Solution:
mL/hr=1000 mL8 hr=125 mL/hr.\text{mL/hr} = \dfrac{1000\
\text{mL}}{8\ \text{hr}} = 125\ \text{mL/hr}.mL/hr=8 hr1000 mL
=125 mL/hr.
Answer: 125 mL/hr.
Rationale:
• Straight division. Common error: forgetting to convert
minutes/hours (not needed here). Saunders recommends
always writing units (mL/hr) to avoid mistakes. Elsevier
Health

, Question 4 — IV flow rate (gtt/min)
Order: Normal saline 750 mL over 6 hr. Tubing drop factor: 15
gtt/mL. What is the rate in gtt/min? (Round to nearest whole
number.)
Solution:
1. mL per minute:
750 mL÷(6 hr×60 min/hr)=750÷360=2.0833 mL/min750\
\text{mL} \div (6\ \text{hr} \times 60\ \text{min/hr}) = 750
\div 360 = 2.0833\
\text{mL/min}750 mL÷(6 hr×60 min/hr)=750÷360=2.0833
mL/min.
2. gtt/min = 2.0833 mL/min×15 gtt/mL=31.25 gtt/min2.0833\
\text{mL/min} \times 15\ \text{gtt/mL} = 31.25\
\text{gtt/min}2.0833 mL/min×15 gtt/mL=31.25 gtt/min.
3. Round to nearest whole number → 31 gtt/min.
Rationale:
• Always multiply mL/min × drop factor. Common mistakes:
using hours instead of minutes when multiplying drop
factor, or not rounding appropriately.


Question 5 — Reconstitution & dosage
Order: Ampicillin 500 mg IV. Stock: vial labeled Powder — 1 g
(1000 mg) per vial. Directions: reconstitute with 4 mL sterile
water to yield 250 mg/mL (assume the label instruction yields