NAPLEX Quiz: Dose Conversions
20 questions · exam conditions
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Dose ConversionsQuestion 1 of 20

Dose is 100 mg/m2/day divided q8h. BSA 1.5 m2. Vial 25 mg/mL. mL/dose?

6 mL per dose
3 mL per dose
2 mL per dose
1.5 mL per dose
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NAPLEX Quiz

NAPLEX Quiz: Dose Conversions

Practice Dose Conversions in NAPLEX with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Dose Conversions, giving you a quick way to practice the rules, question types, and explanations that matter most for NAPLEX.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Dose is 100 mg/m2/day divided q8h. BSA 1.5 m2. Vial 25 mg/mL. mL/dose?

  1. 6 mL per dose
  2. 3 mL per dose
  3. 2 mL per dose (correct answer)
  4. 1.5 mL per dose
Explanation: Start with total daily dose: 100 mg/m2/day times 1.5 m2 = 150 mg/day. Divided q8h means 3 doses/day, so each dose is 150 / 3 = 50 mg. At 25 mg/mL, 50 / 25 = 2 mL/dose. The tempting error is 6 mL, which is the total daily volume before dividing by 3 doses.

Question 2

Child weighs 44 lb. Dose is 6 mg/kg/day divided q8h. Syrup 10 mg/5 mL. mL/dose?

  1. 20 mL per dose (correct answer)
  2. 4 mL per dose
  3. 30 mL per dose
  4. 44 mL per dose
Explanation: Convert 44 lb to kg: 44 / 2.2 = 20 kg. The daily dose is 6 mg/kg * 20 kg = 120 mg, given every 8 hours means 3 doses per day, so each dose is 120 / 3 = 40 mg. The syrup has 10 mg per 5 mL, or 2 mg/mL, so 40 mg / 2 mg/mL = 20 mL per dose. A tempting error is mixing up lb and kg to get 44 mL per dose, but pounds must be converted first.

Question 3

KCl 10% contains 10 g/100 mL. MW 74.5. mL for 20 mEq?

  1. 149 mL
  2. 7.8 mL
  3. 1.49 mL
  4. 14.9 mL (correct answer)
Explanation: Each mEq of KCl is 74.5 mg because potassium has valence 1, so 20 mEq = 1,490 mg = 1.49 g. A 10% solution contains 10 g per 100 mL, or 0.1 g/mL. Divide 1.49 g by 0.1 g/mL to get 14.9 mL. The tempting 1.49 mL comes from stopping at the gram weight without dividing by the 0.1 g/mL concentration.

Question 4

Patient weighs 198 lb. Insulin order 0.5 units/kg/day. U-100. mL/day?

  1. 0.9 mL/day
  2. 0.45 mL/day (correct answer)
  3. 4.5 mL/day
  4. 45 mL/day
Explanation: Convert 198 lb to 90 kg, then multiply by 0.5 units/kg/day to get 45 units/day. U-100 insulin has 100 units per mL, so 45 units divided by 100 units/mL gives 0.45 mL/day. A tempting wrong answer is 0.9 mL/day, which comes from using pounds as kilograms, giving 99 units then rounding.

Question 5

Heparin 18 units/kg/hr. Patient 176 lb. Bag 25,000 units/250 mL. mL/hr?

  1. 14.4 mL/hr (correct answer)
  2. 28.8 mL/hr
  3. 57.6 mL/hr
  4. 1.44 mL/hr
Explanation: Convert 176 lb to 80 kg; 18 units/kg/hr gives 1,440 units/hr. The bag is 25,000 units per 250 mL, so the concentration is 100 units/mL. 1,440 divided by 100 equals 14.4 mL/hr. The tempting 1.44 mL/hr comes from using 1,000 units/mL instead of 100 units/mL, shifting the decimal one place too far.

Question 6

A 52-year-old male (weight 90 kg) with chronic hepatitis C and cirrhosis is being treated for anxiety with lorazepam, but due to excessive sedation the team plans to use a reduced dose. Medical history: cirrhosis (Child-Pugh class C), anxiety. Current medications: spironolactone 100 mg daily, furosemide 40 mg daily, lactulose 20 g three times daily. Labs: AST 110 U/L (normal 10–40), ALT 95 U/L (normal 7–56), total bilirubin 3.2 mg/dL (normal 0.2–1.2), albumin 2.6 g/dL (normal 3.5–5.0). If the usual lorazepam dose is 1 mg by mouth every 8 hours and the plan is to reduce the total daily dose by 50% due to hepatic impairment, determine the appropriate total daily dose for this patient.

  1. 0.5 mg/day
  2. 1.5 mg/day (correct answer)
  3. 3 mg/day
  4. 4.5 mg/day
Explanation: This question evaluates hepatic dose adjustment for lorazepam in a patient with severe liver disease. The key patient-specific factor is Child-Pugh class C cirrhosis with laboratory evidence of severe hepatic dysfunction, including elevated bilirubin and low albumin. The correct answer is 1.5 mg/day, calculated by taking the usual total daily dose of 3 mg/day (1 mg every 8 hours = 3 mg/day) and reducing it by 50% as specified (3 mg × 0.5 = 1.5 mg/day). Option A (0.5 mg/day) incorrectly reduces the dose by approximately 83%, which is excessive. Option C (3 mg/day) fails to implement any dose reduction despite severe hepatic impairment. Option D (4.5 mg/day) incorrectly increases the dose by 50% rather than reducing it. For benzodiazepines in hepatic impairment, dose reductions of 50% or more are often necessary due to decreased metabolism and increased sensitivity, with lorazepam being preferred over other benzodiazepines due to its simpler metabolic pathway.

Question 7

A 72-year-old female (weight 60 kg) with chronic pain is being transitioned from oral morphine to a transdermal fentanyl patch due to poor adherence. Medical history: osteoarthritis, chronic low back pain, mild CKD. Current medications: morphine immediate-release 30 mg by mouth every 6 hours, docusate 100 mg twice daily. Labs: serum creatinine 1.0 mg/dL1.0\ \text{mg/dL} (normal 0.6–1.1), AST/ALT within normal limits. Using the common conversion approximation that a fentanyl patch 25 mcg/hour25\ \text{mcg/hour} is roughly equivalent to 60 mg/day60\ \text{mg/day} of oral morphine, what is the most appropriate fentanyl patch strength for an equivalent total daily opioid dose?

  1. Fentanyl patch 25 mcg/hour
  2. Fentanyl patch 50 mcg/hour (correct answer)
  3. Fentanyl patch 75 mcg/hour
  4. Fentanyl patch 100 mcg/hour
Explanation: This question evaluates opioid conversion from oral morphine to transdermal fentanyl using established conversion ratios. The key factor is calculating the total daily morphine dose and applying the appropriate conversion to fentanyl. The correct answer is fentanyl patch 50 mcg/hour because the patient takes 30 mg every 6 hours = 120 mg/day of oral morphine, and using the conversion that 25 mcg/hour fentanyl ≈ 60 mg/day oral morphine, the equivalent is 120 mg ÷ 60 mg × 25 mcg/hour = 50 mcg/hour. Option A (25 mcg/hour) would only replace 60 mg/day of morphine, providing half the needed analgesia. Option C (75 mcg/hour) would be equivalent to 180 mg/day morphine, a 50% increase. Option D (100 mcg/hour) would double the opioid exposure to 240 mg morphine equivalents daily. When converting to fentanyl patches, calculate the total daily morphine dose first, then use conservative conversion ratios and monitor closely, as individual variation in fentanyl absorption and metabolism can be significant.

Question 8

A 7-year-old male (weight 25 kg) is treated for pinworms with pyrantel pamoate 11 mg/kg as a single dose (maximum 1 g). PMH: none. Current meds: none. Labs: not indicated. What is the correct dose in mg for this patient?

  1. 110 mg once
  2. 275 mg once (correct answer)
  3. 550 mg once
  4. 1000 mg once
Explanation: This question tests weight-based dose calculation with a maximum cap for pediatric antiparasitic therapy. The key patient-specific factor is the child's weight of 25 kg, which determines the dose up to the 1 g maximum. The correct dose is 275 mg once because 11 mg/kg × 25 kg = 275 mg, below the max. Choice A is incorrect as it miscalculates to about 4.4 mg/kg. Choices C and D are wrong; C doubles it, and D exceeds unnecessarily. Multiply mg/kg by weight and apply caps to avoid overdose. Educate on single-dose administration and hygiene to prevent reinfection in pinworm treatment.

Question 9

A 78-year-old female (weight 55 kg, height 158 cm) with chronic pain is taking pregabalin 150 mg by mouth twice daily. She reports increased sedation and has chronic kidney disease. Labs: SCr 1.8 mg/dL. Using Cockcroft-Gault with actual body weight, what dose adjustment is necessary if the recommended regimen for creatinine clearance 30–60 mL/min is 75 mg twice daily?

  1. Adjust to pregabalin 75 mg by mouth twice daily (correct answer)
  2. Continue pregabalin 150 mg by mouth twice daily
  3. Adjust to pregabalin 150 mg by mouth three times daily
  4. Adjust to pregabalin 75 mg by mouth once daily
Explanation: This question tests renal dose adjustment for analgesic therapy. The key patient-specific factor is the creatinine clearance of approximately 22 mL/min, calculated via Cockcroft-Gault using age, weight, and SCr. Adjusting to 75 mg twice daily is accurate as it reduces the daily dose to 150 mg, aligning with maximum recommendations for CrCl 15-30 mL/min to avoid sedation. Choice B is incorrect as continuing 150 mg twice daily (300 mg/day) exceeds the max for low CrCl. Choices C and D are wrong; C increases frequency, and D reduces excessively to once daily. Use the female multiplier (0.85) in Cockcroft-Gault for accurate CrCl in women. Titrate pregabalin slowly in elderly with renal issues, monitoring for CNS side effects.

Question 10

A 61-year-old male (weight 92 kg) with osteomyelitis is stable on linezolid 600 mg by mouth every 12 hours but is now intubated and cannot take oral medications. PMH: type 2 diabetes. Current meds: insulin glargine. Labs: platelets 210 x10^3/mcL, SCr 1.1 mg/dL. Calculate the equivalent IV dose for this oral medication.

  1. Linezolid 300 mg IV every 12 hours
  2. Linezolid 600 mg IV every 12 hours (correct answer)
  3. Linezolid 1200 mg IV every 12 hours
  4. Linezolid 600 mg IV once daily
Explanation: This question tests dose conversion from oral to intravenous formulation for antibiotic therapy. The key patient-specific factor is intubation preventing oral intake, necessitating IV administration. The equivalent IV dose is 600 mg every 12 hours because linezolid has 100% bioavailability, allowing 1:1 conversion. Choice A is incorrect as it halves the dose, risking treatment failure. Choices C and D are wrong; C doubles it, and D reduces frequency. For bioequivalent formulations, maintain dose and frequency in conversions. Monitor platelets weekly during linezolid therapy due to myelosuppression risk.

Question 11

A 58-year-old female (weight 60 kg) is admitted with severe nausea and is NPO. She has been taking metoclopramide 10 mg by mouth four times daily. PMH: GERD. Current meds: pantoprazole 40 mg daily. Labs: SCr 0.7 mg/dL. Calculate the equivalent IV dose for this oral medication (assume IV and oral doses are equivalent).

  1. Metoclopramide 5 mg IV four times daily
  2. Metoclopramide 10 mg IV four times daily (correct answer)
  3. Metoclopramide 20 mg IV four times daily
  4. Metoclopramide 10 mg IV twice daily
Explanation: This question tests dose conversion from oral to intravenous formulation for antiemetic therapy. The key patient-specific factor is the NPO status with severe nausea, necessitating IV administration. The equivalent IV dose is 10 mg four times daily because metoclopramide has high bioavailability, allowing 1:1 conversion. Choice A is incorrect as it halves the dose, reducing prokinetic effect. Choices C and D are wrong; C doubles it, and D halves frequency. Use direct equivalence for drugs with similar IV and PO pharmacokinetics. Monitor for extrapyramidal symptoms, especially in females and prolonged use.

Question 12

A 49-year-old male (weight 78 kg) is being treated for a serious MRSA infection and is stable on doxycycline 100 mg by mouth every 12 hours, but is now NPO for a procedure. PMH: none. Current meds: doxycycline only. Labs: SCr 0.9 mg/dL, AST/ALT normal. Calculate the equivalent IV dose for this oral medication (assume IV and oral doses are equivalent).

  1. Doxycycline 50 mg IV every 12 hours
  2. Doxycycline 100 mg IV every 12 hours (correct answer)
  3. Doxycycline 200 mg IV every 12 hours
  4. Doxycycline 100 mg IV once daily
Explanation: This question tests dose conversion from oral to intravenous formulation for antibiotic therapy. The key patient-specific factor is the NPO status for a procedure, necessitating IV administration. The equivalent IV dose is 100 mg every 12 hours because doxycycline has high bioavailability, allowing 1:1 conversion. Choice A is incorrect as it halves the dose, potentially reducing efficacy against MRSA. Choices C and D are wrong; C doubles it, and D reduces frequency. Maintain dose and interval for bioequivalent conversions. No renal adjustment needed for doxycycline, unlike some antibiotics.

Question 13

A 64-year-old female (weight 68 kg, height 165 cm) with type 2 diabetes is taking metformin immediate-release 1000 mg by mouth twice daily. She is admitted with dehydration and acute kidney injury. Labs: SCr 2.2 mg/dL, bicarbonate 20 mEq/L (22–29). Using Cockcroft-Gault with actual body weight, what dose adjustment is necessary for this patient's renal function if creatinine clearance is < 30 mL/min and metformin should be discontinued?

  1. Continue metformin 1000 mg by mouth twice daily
  2. Reduce metformin to 500 mg by mouth twice daily
  3. Reduce metformin to 500 mg by mouth once daily
  4. Discontinue metformin (correct answer)
Explanation: This question tests renal dose adjustment for antidiabetic therapy. The key patient-specific factor is the creatinine clearance of approximately 28 mL/min, calculated via Cockcroft-Gault using age, weight, and SCr. Discontinuing metformin is accurate as it is contraindicated for CrCl <30 mL/min due to lactic acidosis risk. Choice A is incorrect as continuing risks toxicity in AKI. Choices B and C are wrong; they reduce but do not eliminate use in contraindicated clearance. Use actual body weight in calculations unless adjusted for obesity. Assess for alternative therapies like insulin in renal impairment and diabetes.

Question 14

A 56-year-old female (weight 72 kg) with an acute COPD exacerbation cannot take oral meds due to continuous BiPAP and aspiration risk. She was ordered prednisone 40 mg by mouth daily; the team wants an equivalent IV corticosteroid dose. PMH: COPD, osteoporosis. Current meds: tiotropium, alendronate. Labs: glucose 140 mg/dL. Calculate the equivalent IV dose when switching to methylprednisolone (use equivalence: prednisone 5 mg = methylprednisolone 4 mg).

  1. Methylprednisolone 16 mg IV daily
  2. Methylprednisolone 32 mg IV daily (correct answer)
  3. Methylprednisolone 40 mg IV daily
  4. Methylprednisolone 50 mg IV daily
Explanation: This question tests dose conversion from oral to intravenous corticosteroid using potency equivalence. The key patient-specific factor is the inability to take oral meds due to BiPAP, necessitating IV administration. The equivalent IV dose is 32 mg daily because prednisone 5 mg = methylprednisolone 4 mg, so 40 mg prednisone = 32 mg methylprednisolone. Choice C is incorrect as it ignores the 5:4 ratio, using 1:1. Choices A and D are wrong; A halves incorrectly, and D uses a 4:5 ratio reversal. Apply standard glucocorticoid equivalence ratios for accurate conversions. Monitor glucose levels during corticosteroid therapy, especially in COPD exacerbations.

Question 15

A 70-year-old male (weight 70 kg, height 170 cm) with gout is taking colchicine 0.6 mg by mouth twice daily for prophylaxis. He has worsening renal function. Labs: SCr 2.4 mg/dL. Using Cockcroft-Gault with actual body weight, what dose adjustment is necessary if the recommended prophylaxis for creatinine clearance < 30 mL/min is 0.3 mg once daily?

  1. Continue colchicine 0.6 mg by mouth twice daily
  2. Adjust to colchicine 0.6 mg by mouth once daily
  3. Adjust to colchicine 0.3 mg by mouth once daily (correct answer)
  4. Adjust to colchicine 1.2 mg by mouth once daily
Explanation: This question tests renal dose adjustment for gout prophylaxis. The key patient-specific factor is the creatinine clearance of approximately 28 mL/min, calculated via Cockcroft-Gault using age, weight, and SCr. Adjusting to 0.3 mg once daily is accurate as it matches recommendations for CrCl <30 mL/min to prevent toxicity. Choice A is incorrect as continuing twice daily risks accumulation. Choices B and D are wrong; B halves incorrectly, and D doubles the daily amount. Calculate CrCl precisely in elderly males without the female multiplier. Use lowest effective doses of colchicine in renal impairment to minimize gastrointestinal side effects.

Question 16

A 2-year-old male (weight 12 kg) is diagnosed with streptococcal pharyngitis and is prescribed cephalexin 50 mg/kg/day by mouth divided every 12 hours. PMH: none. Current meds: none. Labs: not indicated. What is the correct dose per administration in mg?

  1. 150 mg by mouth every 12 hours
  2. 300 mg by mouth every 12 hours (correct answer)
  3. 600 mg by mouth every 12 hours
  4. 50 mg by mouth every 12 hours
Explanation: This question tests weight-based dose calculation for pediatric antibiotic therapy. The key patient-specific factor is the child's weight of 12 kg, which determines the total daily dose. The accurate dose per administration is 300 mg every 12 hours because 50 mg/kg/day × 12 kg = 600 mg/day, divided by 2 administrations = 300 mg per dose. Choice A is incorrect as it halves the per-dose amount, likely from misdividing. Choices C and D are wrong; C doubles the dose, and D uses about 8 mg/kg/day. Calculate total daily dose first, then divide by dosing intervals for per-administration amounts. In pediatrics, round to practical suspension strengths and educate on administration techniques.

Question 17

A 40-year-old male (weight 85 kg) is admitted for a skin/soft tissue infection and is unable to take oral therapy due to ileus. He has been taking trimethoprim-sulfamethoxazole (TMP-SMX) DS 1 tablet (160 mg TMP/800 mg SMX) by mouth every 12 hours. PMH: none. Labs: SCr 0.8 mg/dL. Calculate the equivalent IV dose for this oral medication using TMP component equivalence.

  1. TMP-SMX 80 mg TMP IV every 12 hours
  2. TMP-SMX 160 mg TMP IV every 12 hours (correct answer)
  3. TMP-SMX 320 mg TMP IV every 12 hours
  4. TMP-SMX 160 mg TMP IV once daily
Explanation: This question tests dose conversion from oral to intravenous formulation for antibiotic therapy. The key patient-specific factor is the ileus preventing oral intake, necessitating IV administration. The equivalent IV dose is 160 mg TMP every 12 hours because TMP-SMX has high bioavailability, and the TMP component (160 mg) converts 1:1 from DS tablet. Choice A is incorrect as it halves the TMP dose, reducing efficacy. Choices C and D are wrong; C doubles it, and D reduces frequency. Use the active component (e.g., TMP) for equivalence in combination drugs. Confirm renal function, as TMP-SMX requires adjustment in impairment.

Question 18

A 66-year-old male (weight 75 kg, height 178 cm) with a history of DVT is receiving enoxaparin 1 mg/kg subcutaneously every 12 hours. He develops acute kidney injury and the team wants to change to the renal-adjusted regimen. Labs: SCr 2.6 mg/dL, hemoglobin 12.8 g/dL. Using Cockcroft-Gault with actual body weight, what dose adjustment is necessary if creatinine clearance is < 30 mL/min and the adjusted dose is 1 mg/kg subcutaneously once daily?

  1. Change to enoxaparin 75 mg subcutaneously once daily (correct answer)
  2. Change to enoxaparin 75 mg subcutaneously every 12 hours
  3. Change to enoxaparin 150 mg subcutaneously once daily
  4. Continue enoxaparin 1 mg/kg subcutaneously every 12 hours
Explanation: This question tests renal dose adjustment for anticoagulant therapy. The key patient-specific factor is the creatinine clearance of approximately 30 mL/min, calculated via Cockcroft-Gault using age, weight, and SCr. Changing to 75 mg subcutaneously once daily is accurate as it matches the 1 mg/kg once daily recommendation for CrCl <30 mL/min to avoid bleeding. Choice B is incorrect as it maintains every 12 hours, risking accumulation. Choices C and D are wrong; C doubles the dose, and D continues unadjusted. Always use actual body weight for enoxaparin dosing unless specified otherwise. Monitor anti-Xa levels in renal impairment for therapeutic confirmation.

Question 19

A 52-year-old female (weight 65 kg) with severe nausea is admitted for hyperemesis and cannot take oral medications. She takes ondansetron 8 mg by mouth every 8 hours at home. PMH: migraines. Current meds: sumatriptan PRN. Labs: potassium 3.9 mEq/L (3.5–5.0), magnesium 1.9 mg/dL (1.7–2.2). Calculate the equivalent IV dose for this oral medication (assume IV and oral doses are equivalent).

  1. Ondansetron 4 mg IV every 8 hours
  2. Ondansetron 8 mg IV every 8 hours (correct answer)
  3. Ondansetron 16 mg IV every 8 hours
  4. Ondansetron 8 mg IV once daily
Explanation: This question tests dose conversion from oral to intravenous formulation for antiemetic therapy. The key patient-specific factor is the inability to take oral medications due to hyperemesis, necessitating IV administration. The equivalent IV dose is 8 mg every 8 hours because ondansetron has high oral bioavailability, allowing 1:1 conversion from the oral regimen. Choice A is incorrect as it halves the dose, potentially reducing efficacy. Choices C and D are wrong; C doubles it, risking QT prolongation, and D reduces frequency. For drugs with equivalent IV and PO dosing, direct conversion maintains exposure. Monitor electrolytes like potassium and magnesium, as imbalances can exacerbate nausea or arrhythmia risks.

Question 20

An 84-year-old female (weight 55 kg, height 160 cm) is started on gabapentin for postherpetic neuralgia. Medical history: CKD stage 3, osteoarthritis. Current medications: acetaminophen 650 mg three times daily as needed. Labs: serum creatinine 1.3 mg/dL1.3\ \text{mg/dL} (normal 0.6–1.1). Using Cockcroft–Gault for females: CrCl=(140−age)×weight72×SCr×0.85\text{CrCl} = \frac{(140-\text{age})\times \text{weight}}{72\times \text{SCr}}\times 0.85, and recommended gabapentin total daily dose for CrCl 30–59 mL/min is 400–1400 mg/day, while for CrCl 15–29 mL/min is 200–700 mg/day. What dose adjustment is necessary for this patient's renal function if the intended regimen was gabapentin 300 mg by mouth three times daily?

  1. Continue 300 mg by mouth three times daily (no change)
  2. Adjust to 300 mg by mouth once daily
  3. Adjust to 300 mg by mouth twice daily (correct answer)
  4. Adjust to 600 mg by mouth three times daily
Explanation: This question tests renal dose adjustment for gabapentin using the Cockcroft-Gault equation in an elderly female patient. The key patient-specific factors are advanced age (84 years), female sex, and elevated serum creatinine (1.3 mg/dL). The correct answer is 300 mg by mouth twice daily because the calculated CrCl = [(140-84) × 55 × 0.85] / (72 × 1.3) = 28.0 mL/min, which falls in the 15-29 mL/min range requiring significant dose reduction. The intended dose of 900 mg/day (300 mg three times daily) exceeds the maximum recommended 700 mg/day for this CrCl range, so reducing to 600 mg/day (300 mg twice daily) is appropriate. Option A (no change) maintains 900 mg/day, which exceeds recommendations. Option B (300 mg once daily) reduces too aggressively to 300 mg/day. Option D (600 mg three times daily) inappropriately doubles the dose to 1800 mg/day. When adjusting gabapentin for renal function, use the Cockcroft-Gault equation with the 0.85 correction factor for females, and ensure the total daily dose falls within the recommended range for the calculated CrCl.