NAPLEX Quiz: Dose Conversions

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.

Question 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

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 15

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.

Question 16

1. 1 inhalation twice daily (correct answer)
2. 2 inhalations once daily
3. 2 inhalations twice daily
4. 1 inhalation once daily

Explanation: This question evaluates inhaled corticosteroid dose conversion based on maintaining equivalent total daily micrograms. The key factor is converting between different strengths of the same medication while maintaining therapeutic equivalence. The correct answer is 1 inhalation twice daily because the current regimen delivers 440 mcg/day (110 mcg × 2 inhalations × 2 times daily), and using the 220 mcg strength requires 440 mcg ÷ 220 mcg = 2 inhalations total per day, which equals 1 inhalation twice daily. Option B (2 inhalations once daily) delivers the correct total daily dose but changes the dosing frequency, which may affect asthma control. Option C (2 inhalations twice daily) doubles the dose to 880 mcg/day. Option D (1 inhalation once daily) halves the dose to 220 mcg/day. When converting between inhaler strengths, calculate the total daily micrograms first, then determine the number of inhalations needed with the new strength while preferably maintaining the same dosing frequency for consistent symptom control.

Question 17

1. Continue rivaroxaban 20 mg by mouth once daily
2. Adjust to rivaroxaban 15 mg by mouth once daily (correct answer)
3. Adjust to rivaroxaban 10 mg by mouth once daily
4. Hold rivaroxaban because creatinine clearance is > 50 mL/min

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, height (if needed), and SCr. Adjusting to 15 mg once daily is accurate as it follows recommendations for CrCl 15-50 mL/min to prevent bleeding risks from accumulation. Choice A is incorrect as continuing 20 mg risks overdose in reduced clearance. Choices C and D are wrong; C further reduces unnecessarily, and D holds incorrectly since CrCl is <50 but >15. Use Cockcroft-Gault formula accurately, applying the 0.85 multiplier for females. Monitor for bleeding and consider alternative anticoagulants if CrCl falls below 15 mL/min.

Question 18

1. 140 mg by mouth every 6 hours
2. 350 mg by mouth every 6 hours (correct answer)
3. 700 mg by mouth every 6 hours
4. 1400 mg by mouth every 6 hours

Explanation: This question tests weight-based dose calculation for pediatric antibiotic therapy. The key patient-specific factor is the child's weight of 35 kg, which determines the total daily dose. The appropriate dose per administration is 350 mg every 6 hours because 40 mg/kg/day × 35 kg = 1400 mg/day, divided by 4 = 350 mg per dose. Choice A is incorrect as it misdivides to every 6 hours dose of about 4 mg/kg. Choices C and D are wrong; C halves daily total, and D is daily total. Ensure correct division by the number of daily doses after calculating total. Round to available capsule strengths if needed for older children.

Question 19

1. 495 mg/day
2. 990 mg/day (correct answer)
3. 45 mg/day
4. 1980 mg/day

Explanation: This question tests the ability to calculate a weight-based pediatric dose conversion from mg/kg/day to total daily dose. The key patient-specific factor is the child's weight of 22 kg, which is essential for converting the prescribed dose of 45 mg/kg/day. The correct answer is 990 mg/day, calculated by multiplying 45 mg/kg/day × 22 kg = 990 mg/day. Option A (495 mg/day) incorrectly divides the total daily dose by 2, confusing the per-dose amount with the total daily dose. Option C (45 mg/day) erroneously uses the mg/kg/day value without multiplying by the patient's weight. Option D (1980 mg/day) doubles the correct answer, possibly misunderstanding that the dose is already expressed as a daily total. When calculating pediatric doses, always multiply the mg/kg/day dose by the patient's weight in kg to obtain the total daily dose, then divide by the number of doses per day if individual doses are needed.

Question 20

1. Levofloxacin 250 mg IV once daily
2. Levofloxacin 750 mg IV once daily (correct answer)
3. Levofloxacin 1500 mg IV once daily
4. Levofloxacin 750 mg IV every 12 hours

Explanation: This question evaluates understanding of oral-to-IV dose conversion for levofloxacin, which has 100% bioavailability. The key patient-specific factor is that the patient cannot take oral medications due to vomiting, necessitating IV administration. The correct answer is 750 mg IV once daily because levofloxacin has essentially complete oral bioavailability, making the IV dose equivalent to the oral dose on a 1:1 basis. Option A (250 mg) incorrectly reduces the dose by approximately 67%, which would result in subtherapeutic levels. Option C (1500 mg) doubles the dose unnecessarily, potentially increasing the risk of adverse effects. Option D (750 mg every 12 hours) maintains the correct single dose but doubles the daily exposure by changing the frequency. For medications with high oral bioavailability like levofloxacin, the IV dose typically equals the oral dose, making conversions straightforward when switching routes of administration.