- A 9 kg infant is ordered a single dose of an antibiotic IM at 25 mg/kg. The medication is reconstituted to a concentration of 150 mg/mL. The maximum recommended volume for a single IM injection in the vastus lateralis muscle of an infant is 1 mL. What is the most appropriate nursing action?
Answer: Divide the dose into two separate injections of 0.75 mL each.
First, calculate the required dose in mg: 9 kg * 25 mg/kg = 225 mg. Second, calculate the volume required for this dose: 225 mg / 150 mg/mL = 1.5 mL. Third, compare the required volume to the maximum single injection volume. Since 1.5 mL exceeds the 1 mL maximum, the dose must be split into two separate injections. Each injection would be 1.5 mL / 2 = 0.75 mL. Administering 1 mL and discarding the rest would result in significant underdosing. Requesting a lower dose is inappropriate as the current dose is likely correct therapeutically. Administering the full volume in one site would violate safe practice guidelines.
- A pharmacist receives an order for cefdinir for a 28 lb child. The order is for 7 mg/kg once daily for 10 days. The available suspension is 125 mg/5 mL. What is the volume for a single daily dose, and what is the total volume to dispense for the full course?
Answer: 3.6 mL per dose; dispense 36 mL total
First, convert weight to kg: 28 lbs / 2.2 lbs/kg = 12.73 kg. Second, calculate the daily dose in mg: 12.73 kg 7 mg/kg = 89.1 mg. Third, calculate the volume for a single daily dose: (89.1 mg / 125 mg) 5 mL = 3.56 mL, which rounds to 3.6 mL. Fourth, calculate the total volume for the 10-day course: 3.6 mL/day * 10 days = 36 mL. The pharmacy would likely dispense a standard 60 mL bottle, but the total required volume is 36 mL. Answer choice A is the most precise. Distractor C results from calculating the dose without converting pounds to kilograms (28 * 7 = 196 mg; (196/125)*5 = 7.84 mL). Distractors B and D list correct single dose volumes but incorrect total volumes or vice-versa, testing attention to both parts of the question.
- A 10 kg infant is prescribed furosemide oral solution 1 mg/kg/dose twice daily. The available solution has a concentration of 10 mg/mL. The parents have a 1 mL oral syringe with 0.1 mL markings. What volume should the pharmacist instruct the parents to draw up for each dose?
Answer: 1.0 mL
First, calculate the required dose in mg: 10 kg * 1 mg/kg/dose = 10 mg. Second, calculate the volume of the 10 mg/mL solution required: 10 mg / 10 mg/mL = 1.0 mL. This volume is easily and accurately measured with the provided 1 mL syringe. The other answer choices represent significant dosing errors. Distractor A is a tenfold underdose. Distractor D is a twofold overdose. Distractor B is half the correct dose.
- 6-kg child, 5 mcg/kg/min, solution 250 mcg/mL. Pump mL/h?
Answer: 7.2 mL/h
First find the dose per minute: 6 kg times 5 mcg/kg/min = 30 mcg/min. Over one hour that is 30 times 60 = 1,800 mcg/h. Divide by the concentration, 250 mcg/mL: 1,800 / 250 = 7.2 mL/h. The 0.12 mL/h trap is the per-minute volume, not the hourly pump rate.
- A 3-year-old weighing 15 kg is prescribed prednisolone oral solution (15 mg/5 mL) for an asthma exacerbation. The order is for 2 mg/kg/day for 5 days. What is the total volume of medication, in mL, that should be dispensed for the entire course of therapy?
Answer: 50 mL
This multi-step problem requires calculating the total volume for the full therapy duration. First, calculate the total daily dose in mg: 15 kg 2 mg/kg/day = 30 mg/day. Second, calculate the volume needed per day: (30 mg / 15 mg) 5 mL = 10 mL/day. Third, calculate the total volume for the 5-day course: 10 mL/day * 5 days = 50 mL. Dispensing 10 mL would only be enough for one day. Dispensing 20 mL would be enough for two days. Dispensing 100 mL would be a 10-day supply.
- A mother asks for a dose of diphenhydramine for her 4-year-old daughter who weighs 16 kg. The pharmacist knows the correct weight-based dose is 1.25 mg/kg every 6 hours. The product label provides dosing by age: 'Ages 2-5: do not use unless directed by a doctor. Ages 6-11 years: 12.5 to 25 mg.' Based on a weight-based calculation, what is the most appropriate single dose to recommend?
Answer: 20.0 mg
When you encounter pediatric dosing questions, always prioritize weight-based calculations over age-based recommendations, as they provide more accurate and safer dosing for individual patients.
To find the correct dose, you need to multiply the child's weight by the recommended dose per kilogram: 16 kg×1.25 mg/kg=20 mg. This gives you the appropriate single dose for this specific child.
The correct answer is D) 20.0 mg, which matches your weight-based calculation exactly.
Now let's examine why the other options are incorrect. Choice A) 12.5 mg represents the lower end of the age-based dosing range for 6-11 year olds, but this child is only 4 years old, and more importantly, this dose would be too low based on her actual weight (only 0.78 mg/kg). Choice B) 40.0 mg is dangerously high—it's double the calculated dose and would deliver 2.5 mg/kg, potentially causing toxicity. Choice C) 25.0 mg represents the upper limit for the 6-11 age group and exceeds the safe weight-based dose for this child (1.56 mg/kg).
Remember this key principle: weight-based dosing trumps age-based dosing in clinical practice because children of the same age can vary significantly in size and drug metabolism. Always calculate the mg/kg dose first, then check if it falls within safe parameters. This approach ensures both efficacy and safety in pediatric pharmacotherapy. - 24-lb child, 60 mg/kg/day divided q8h. Stock 100 mg/mL. Give?
Answer: 2.2 mL
Convert 24 lb to kg: 24 / 2.2 = 10.9 kg. Daily dose is 10.9 x 60 = 655 mg, divided q8h means 3 doses: 655 / 3 = 218 mg per dose. At 100 mg/mL, give 218 / 100 = 2.2 mL. The tempting error is 6.5 mL, the total daily volume if you skip dividing by 3.
- An oncologist writes an order for methotrexate for a 5-year-old child weighing 18 kg with a Body Surface Area (BSA) of 0.75 m². The protocol calls for a dose of 20 mg/m². The pharmacy has 50 mg/2 mL vials. An intern calculates the dose based on weight instead of BSA, using a conversion of 1 mg/kg. What is the difference in mg between the correct dose and the intern's incorrectly calculated dose?
Answer: 3 mg
When you encounter pediatric dosing calculations, always pay close attention to whether the dose should be calculated by weight (mg/kg) or body surface area (mg/m²). Many chemotherapy drugs like methotrexate use BSA-based dosing because it more accurately reflects metabolic capacity and drug clearance in children.
Let's calculate both doses to find the difference. The correct dose uses BSA: 20 mg/m²×0.75 m²=15 mg
The intern's incorrect calculation uses weight: 1 mg/kg×18 kg=18 mg
The difference between these doses is: 18 mg−15 mg=3 mg
Looking at the wrong answers: Choice A (2 mg) might result from calculation errors in the subtraction. Choice B (15 mg) represents the correct BSA-based dose itself, not the difference between doses. Choice C (5 mg) could come from misreading the protocol dose or making arithmetic errors in the BSA calculation.
Choice D (3 mg) correctly represents the difference between the weight-based and BSA-based calculations.
Key strategy: Always verify the dosing method specified in pediatric questions. BSA-based dosing is standard for most chemotherapy agents because it accounts for physiological differences better than weight alone. Double-check your arithmetic by working backwards—if the difference is 3 mg and the correct dose is 15 mg, the incorrect dose should be 18 mg, which matches our weight-based calculation. - A 33 lb child is prescribed ceftriaxone 750 mg IV once daily. The recommended dose for this indication is 50-75 mg/kg/day. The drug is reconstituted to a final concentration of 100 mg/mL. Which statement is correct?
Answer: The prescribed dose is correct, and the volume to administer is 7.5 mL.
First, convert the weight to kg: 33 lbs / 2.2 lbs/kg = 15 kg. Second, calculate the therapeutic dose range: Lower limit = 15 kg 50 mg/kg/day = 750 mg/day. Upper limit = 15 kg 75 mg/kg/day = 1125 mg/day. The prescribed dose of 750 mg/day falls at the lower end of the therapeutic range, so it is a correct dose. Third, calculate the volume to administer: 750 mg / 100 mg/mL = 7.5 mL. Therefore, the dose is correct and the volume is 7.5 mL. Distractor C and D incorrectly assess the dose. Distractor A has the incorrect volume.
- A 16-year-old male weighing 95 kg is prescribed a single dose of an analgesic for acute pain. The recommended pediatric dose is 10 mg/kg. The standard maximum single dose for an adult is 800 mg. Which dose should be administered?
Answer: 800 mg
This question requires a multi-step thought process. First, calculate the weight-based dose: 95 kg * 10 mg/kg = 950 mg. Second, compare this calculated dose to the maximum adult dose. Since 950 mg exceeds the maximum single adult dose of 800 mg, the dose should be capped at the maximum. Therefore, 800 mg is the most appropriate dose to administer. In pediatrics, especially with larger adolescents, the calculated weight-based dose should never exceed the standard adult maximum dose.
- A 22 lb toddler is prescribed an oral medication at a dose of 5 mg/kg. The medication is supplied as a 200 mg/5 mL suspension. Which volume should be administered for a single dose?
Answer: 1.25 mL
First, convert the weight from pounds to kilograms: 22 lbs / 2.2 lbs/kg = 10 kg. Next, calculate the required dose in mg: 10 kg 5 mg/kg = 50 mg. Finally, calculate the volume of the suspension needed to provide this dose: (50 mg / 200 mg) 5 mL = 1.25 mL. Distractor B (2.50 mL) would be correct if the concentration was 100 mg/5 mL. Distractor C (5.50 mL) results from incorrectly calculating the dose based on the weight in pounds (22 lbs * 5 mg/kg = 110 mg; (110/200)*5 = 2.75 mL, this isn't C. Let's re-evaluate distractors. Error: using 22 kg instead of 10 kg. Dose = 22*5 = 110 mg. Volume = (110/200)*5 = 2.75mL. Still not there. Error: using lbs as kg, and miscalculating volume. Maybe (22 lbs * 5 mg/kg) = 110 mg, and then they confuse the concentration to be 100 mg/5ml -> 5.5ml. This is plausible. Distractor D (12.5 mL) could result from a decimal placement error or miscalculation.
- A 5-year-old child weighing 44 lbs is to receive a loading dose of phenobarbital at 20 mg/kg. The drug is available in an injectable form with a concentration of 65 mg/mL. What volume should be drawn up for this dose?
Answer: 6.2 mL
First, convert the child's weight to kilograms: 44 lbs / 2.2 lbs/kg = 20 kg. Second, calculate the total loading dose in mg: 20 kg 20 mg/kg = 400 mg. Third, calculate the volume of the 65 mg/mL solution needed: 400 mg / 65 mg/mL = 6.15 mL. The closest answer is 6.2 mL. Distractor A (3.1 mL) is an error of dividing the correct answer by two. Distractor C (13.5 mL) results from failing to convert the weight from pounds to kilograms (44 20 = 880 mg; 880/65 = 13.5 mL), a very common error. Distractor D is a significant miscalculation.
- A prescription for a 12 kg child is written for vancomycin 160 mg IV Q6H. The standard pediatric dosing guidelines for this indication are 40-60 mg/kg/day. Which statement accurately assesses this dose?
Answer: The dose is appropriate and falls within the upper end of the therapeutic range.
First, calculate the total daily dose prescribed: 160 mg/dose * 4 doses/day (Q6H) = 640 mg/day. Second, calculate the dose in mg/kg/day for this patient: 640 mg/day / 12 kg = 53.3 mg/kg/day. Third, compare this to the recommended range of 40-60 mg/kg/day. The calculated dose of 53.3 mg/kg/day falls within this range, towards the upper end. Therefore, the dose is appropriate. A calculation error, such as assuming Q8H (3 doses/day), would lead to 160*3/12 = 40 mg/kg/day, suggesting the dose is at the lower end (distractor B). Misinterpreting the range or a calculation mistake could lead to concluding the dose is subtherapeutic (A) or supratherapeutic (D).
- An 8 kg infant requires an IV antibiotic at a dose of 60 mg/kg/day, administered as a continuous 24-hour infusion. The drug is supplied from the pharmacy in a 500 mg/100 mL bag of normal saline. At what rate (mL/hr) should the infusion pump be set to deliver the correct dose?
Answer: 4.0 mL/hr
This is a multi-step calculation. First, calculate the total daily dose in mg: 60 mg/kg/day 8 kg = 480 mg/day. Second, determine the total volume needed to supply this dose using the provided concentration: (480 mg / 500 mg) 100 mL = 96 mL. Third, calculate the infusion rate by dividing the required volume by the infusion time: 96 mL / 24 hours = 4.0 mL/hr. Distractor C (4.2 mL/hr) results from incorrectly assuming the entire 100 mL bag should be infused over 24 hours. Distractor A (2.0 mL/hr) is a simple calculation error (e.g., dividing the final answer by 2). Distractor D (20.0 mL/hr) represents the dose in mg/hr (480 mg / 24 hr = 20 mg/hr), a common error of confusing mass rate with volume rate.
- A pharmacist needs to prepare an acyclovir suspension for a 38 lb child with a herpes simplex infection. The dose is 20 mg/kg/dose given four times a day. The pharmacy will compound a 200 mg/5 mL suspension. What volume, in mL, is required for a single dose?
Answer: 8.6 mL
When you encounter pediatric dosing calculations, you need to systematically convert units, calculate the patient-specific dose, and then determine the volume needed from the available concentration.
Start by converting the child's weight from pounds to kilograms: 38 lb÷2.2=17.27 kg. Next, calculate the dose per administration: 17.27 kg×20 mg/kg=345.4 mg. Finally, determine the volume needed from the 200 mg/5 mL suspension using the proportion: 5 mL200 mg=x mL345.4 mg. Solving for x: x=200345.4×5=8.635 mL, which rounds to 8.6 mL.
Choice A (4.3 mL) represents exactly half the correct volume—this error occurs if you forget to convert pounds to kilograms and use the pound weight directly in the calculation. Choice B (34.5 mL) results from calculating the total daily dose (345.4 mg) but forgetting to convert to volume using the suspension concentration. Choice C (19.0 mL) happens if you incorrectly convert the weight (using 1.0 instead of 2.2 as the conversion factor) then calculate the volume.
For pediatric calculations, always follow the same sequence: convert weight to kg, calculate mg dose, then convert to volume. Double-check your unit conversions—the 2.2 conversion factor from pounds to kilograms is critical and frequently tested. - A 7-month-old infant weighs 16 lbs 8 oz. The infant is prescribed oral ibuprofen for fever at 10 mg/kg per dose. Using the available infant drops with a concentration of 50 mg/1.25 mL, what is the most appropriate volume to administer per dose?
Answer: 1.88 mL
This question requires conversion of mixed units (lbs and oz) and multiple calculation steps. First, convert the weight to a single unit: 8 oz is 0.5 lbs, so the total weight is 16.5 lbs. Second, convert pounds to kilograms: 16.5 lbs / 2.2 lbs/kg = 7.5 kg. Third, calculate the dose in mg: 7.5 kg 10 mg/kg = 75 mg. Finally, calculate the volume: (75 mg / 50 mg) 1.25 mL = 1.875 mL. This rounds to 1.88 mL. Distractor C (2.06 mL) results from incorrectly converting the weight (e.g., using 16.8 lbs instead of 16.5 lbs). Distractor A is a miscalculation. Distractor D results from using the weight in pounds without conversion (16.5 * 10 = 165 mg; (165/50)*1.25 = 4.125 mL).
- A 2-year-old child who weighs 13 kg has been taking an anticonvulsant oral solution (50 mg/mL) at a volume of 1.2 mL twice daily. At a routine checkup six months later, the child's weight is now 15 kg. The target maintenance dose for this drug is 10-15 mg/kg/day. What is the current dose in mg/kg/day and the most appropriate action?
Answer: 8 mg/kg/day; the dose is now subtherapeutic and should be increased.
First, calculate the total daily mg dose the child is receiving: 1.2 mL/dose × 50 mg/mL × 2 doses/day = 120 mg/day. Second, calculate the current mg/kg/day dose based on the new weight of 15 kg: 120 mg/day ÷ 15 kg = 8 mg/kg/day. Third, compare this to the therapeutic range of 10-15 mg/kg/day. The current dose of 8 mg/kg/day is below the therapeutic range, so it is subtherapeutic and needs to be increased. Distractor B would require 150 mg/day (10 mg/kg × 15 kg). Distractor C shows the dose based on the old weight (120 mg ÷ 13 kg = 9.2 mg/kg), which is still subtherapeutic. Distractor D represents a miscalculation.
- A 30 kg child is receiving a medication as a continuous IV infusion. The order is for 5 mcg/kg/min. The drug is supplied in a concentration of 250 mg in 250 mL of D5W. What is the correct infusion rate in mL/hr?
Answer: 9.0 mL/hr
When you encounter IV infusion rate calculations, you need to systematically convert the ordered dose to the final infusion rate using dimensional analysis. This requires careful attention to units and multiple conversion steps.
Start with the ordered dose: 5 mcg/kg/min for a 30 kg child equals 150 mcg/min total dose. Next, convert the drug concentration to compatible units. The supplied concentration is 250 mg in 250 mL, which equals 1 mg/mL or 1000 mcg/mL.
Now calculate the infusion rate: 1000 mcg/mL150 mcg/min=0.15 mL/min
Finally, convert to mL/hr: 0.15 mL/min×60 min/hr=9.0 mL/hr
Answer D (9.0 mL/hr) is correct.
Answer A (4.5 mL/hr) represents a calculation error, likely forgetting to multiply by 60 when converting minutes to hours. Answer B (90.0 mL/hr) suggests a decimal point error or confusion with unit conversions – this rate would deliver 10 times the intended dose. Answer C (15.0 mL/hr) appears to result from miscalculating the weight-based dose or making an error in the concentration conversion.
For IV calculation success, always work methodically: calculate total dose per minute, convert drug concentration to matching units, find mL/min, then convert to mL/hr. Double-check your final answer by working backwards – does this rate deliver the intended dose per minute? - A 10-year-old boy weighing 50 kg has a Body Mass Index >97th percentile. He is prescribed a hydrophilic antibiotic at 20 mg/kg/day, divided Q8H. For this medication, dosing in obese patients should be based on Ideal Body Weight (IBW), which is 38 kg for this patient. The maximum adult dose is 1 g/day. What is the appropriate single dose to administer every 8 hours?
Answer: 253 mg
The question specifies that dosing should be based on Ideal Body Weight (IBW), which is 38 kg. First, calculate the total daily dose using IBW: 20 mg/kg/day 38 kg = 760 mg/day. This is below the 1 g/day maximum. Next, since the dose is divided Q8H (three times a day), calculate the single dose: 760 mg/day / 3 doses = 253.3 mg per dose. The closest answer is 253 mg. Distractor B (333 mg) is calculated using the actual body weight (50 kg 20 mg/kg/day = 1000 mg/day; 1000/3 = 333 mg), which is a common error. Distractors C and D result from misinterpreting the frequency or daily dose calculation.
- A 6-year-old boy (21 kg) is prescribed drug X at 5 mg/kg Q6H. The maximum recommended daily dose for a pediatric patient is 500 mg. Which is the correct single dose to administer?
Answer: 105 mg
This question tests the ability to distinguish between a single dose calculation and a total daily dose limit. First, calculate the single dose based on the order: 21 kg 5 mg/kg = 105 mg. Second, verify that the total daily dose does not exceed the maximum. The frequency is Q6H, which is 4 times a day. Total daily dose = 105 mg/dose 4 doses = 420 mg/day. Since 420 mg is less than the 500 mg maximum daily dose, the calculated single dose of 105 mg is correct. Distractor C (420 mg) is the total daily dose, not the single dose. Distractor B (125 mg) would be the single dose if the maximum daily dose of 500 mg was divided by 4. Distractor D (500 mg) is the maximum daily dose.
