NAPLEX Quiz: Rates Of Administration
20 questions · exam conditions
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Rates Of AdministrationQuestion 1 of 20

A 27-year-old female (weight 65 kg) is admitted for diabetic ketoacidosis and is started on an insulin infusion after initial fluid resuscitation. Labs: SCr 0.9 mg/dL, Na 130 mEq/L, K 4.8 mEq/L, glucose 520 mg/dL. Regular insulin is prepared as 100 units in 100 mL (1 unit/mL), and the order is to start at 0.1 unit/kg/hr. Calculate the infusion rate in mL/hr.

3.25 mL/hr
6.5 mL/hr
13 mL/hr
65 mL/hr
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NAPLEX Quiz

NAPLEX Quiz: Rates Of Administration

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

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

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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.

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Question 1

A 27-year-old female (weight 65 kg) is admitted for diabetic ketoacidosis and is started on an insulin infusion after initial fluid resuscitation. Labs: SCr 0.9 mg/dL, Na 130 mEq/L, K 4.8 mEq/L, glucose 520 mg/dL. Regular insulin is prepared as 100 units in 100 mL (1 unit/mL), and the order is to start at 0.1 unit/kg/hr. Calculate the infusion rate in mL/hr.

  1. 3.25 mL/hr
  2. 6.5 mL/hr (correct answer)
  3. 13 mL/hr
  4. 65 mL/hr

Explanation: The foundational pharmacy concept being tested is weight-based insulin infusion rates for metabolic emergencies like DKA. The key patient-specific factor influencing the rate calculation is the patient's weight of 65 kg and elevated glucose, guiding initial dosing. The correct answer is 6.5 mL/hr, calculated as (0.1 unit/kg/hr × 65 kg = 6.5 units/hr) / 1 unit/mL = 6.5 mL/hr. Choice A (3.25 mL/hr) may result from halving; choice C (13 mL/hr) could be doubling; choice D (65 mL/hr) might arise from omitting concentration. Common misconceptions include unit mismatches. A pearl is to adjust based on hourly glucose checks. Incorporate safety checks like double verification for insulin rates.

Question 2

A 60-year-old female (weight 74 kg) is admitted for septic shock and is started on norepinephrine. Past medical history includes chronic kidney disease stage 2. Labs: SCr 1.2 mg/dL, Na 135 mEq/L, K 4.5 mEq/L, glucose 140 mg/dL. Norepinephrine is prepared as 4 mg in 250 mL (16 mcg/mL), and the order is to infuse at 0.05 mcg/kg/min. Calculate the infusion rate in mL/hr.

  1. 6.9 mL/hr
  2. 13.9 mL/hr (correct answer)
  3. 27.8 mL/hr
  4. 41.7 mL/hr

Explanation: The foundational pharmacy concept being tested is weight-based vasopressor rate calculation in shock states. The key patient-specific factor influencing the rate calculation is the patient's weight of 74 kg and septic shock, demanding precise dosing. The correct answer is 13.9 mL/hr, from (0.05 mcg/kg/min × 74 kg × 60 min/hr = 222 mcg/hr) / 16 mcg/mL ≈ 13.875 mL/hr, rounded to 13.9. Choice A (6.9 mL/hr) may come from halving; choice C (27.8 mL/hr) could be doubling; choice D (41.7 mL/hr) might stem from 0.15 mcg/kg/min. Common misconceptions include forgetting the 60 multiplier. Clinically, titrate to mean arterial pressure. Use consistent units and round appropriately for pump settings.

Question 3

A 59-year-old male (weight 88 kg) is intubated in the ICU and requires continuous sedation. Past medical history includes obstructive sleep apnea and hypertension. Labs: SCr 1.0 mg/dL, Na 140 mEq/L, K 4.4 mEq/L, glucose 120 mg/dL. Propofol is supplied as 10 mg/mL, and the order is to start propofol at 20 mcg/kg/min. Calculate the infusion rate in mL/hr.

  1. 5.3 mL/hr
  2. 10.6 mL/hr (correct answer)
  3. 21.1 mL/hr
  4. 26.4 mL/hr

Explanation: The foundational pharmacy concept being tested is weight-based dosing and rate calculation for continuous sedative infusions. The key patient-specific factor influencing the rate calculation is the patient's weight of 88 kg, directly used in dosing. The correct answer is 10.6 mL/hr, calculated as [dose (20 mcg/kg/min) × weight (88 kg) × 60 min/hr] / concentration (10,000 mcg/mL) = (20 × 88 × 60) / 10,000 = 105,600 / 10,000 = 10.56 mL/hr, rounded to 10.6. Choice A (5.3 mL/hr) may come from halving dose or weight; choice C (21.1 mL/hr) could be from doubling; choice D (26.4 mL/hr) might stem from concentration error (e.g., 4,000 mcg/mL). Distractors often involve unit conversion mistakes. Clinically, titrate propofol based on sedation scales in intubated patients. Always convert all units consistently before calculating.

Question 4

A 49-year-old female (weight 58 kg) is hospitalized for osteomyelitis and is ordered cefepime. Past medical history includes chronic kidney disease stage 3. Labs: SCr 1.9 mg/dL, Na 140 mEq/L, K 4.2 mEq/L, glucose 110 mg/dL. The order is cefepime 2 g IV in a total volume of 100 mL to infuse over 60 minutes. Calculate the mL/hr rate for the ordered medication.

  1. 50 mL/hr
  2. 75 mL/hr
  3. 100 mL/hr (correct answer)
  4. 200 mL/hr

Explanation: The foundational pharmacy concept being tested is infusion rate setup for cephalosporins in bone infections with renal considerations. The key patient-specific factor influencing the rate calculation is the patient's chronic kidney disease stage 3, influencing dosing but not rate directly. The correct answer is 100 mL/hr, from total volume / time (100 mL / 1 hr, as 60 min = 1 hr = 100 mL/hr), suitable for 2 g. Choice A (50 mL/hr) may come from 2 hours; choice B (75 mL/hr) could be misdivision; choice D (200 mL/hr) might be from 30 minutes. Errors often from time misinterpretation. Clinically, adjust doses, not rates, for CKD in antibiotics. Use electronic health records to flag rate limits.

Question 5

A 64-year-old female (weight 55 kg) is hospitalized for weakness and is found to have hypokalemia after several days of diuretic use and poor intake. Medical history includes hypertension and chronic kidney disease stage 2. Labs: SCr 1.0 mg/dL, Na 139 mEq/L, K 2.8 mEq/L, Mg 1.9 mg/dL. The provider orders potassium chloride 40 mEq IV diluted in 250 mL of 0.9% sodium chloride to infuse over 4 hours. Calculate the mL/hr rate for the ordered medication infusion.

  1. 31.25 mL/hr
  2. 50 mL/hr
  3. 62.5 mL/hr (correct answer)
  4. 125 mL/hr

Explanation: The foundational pharmacy concept being tested is calculating infusion rates for electrolyte replacement to avoid complications like arrhythmias. The key patient-specific factor influencing the rate calculation is the patient's hypokalemia and chronic kidney disease, guiding safe potassium infusion speeds. The correct answer is 62.5 mL/hr, using the formula total volume / infusion time (250 mL / 4 hr = 62.5 mL/hr), appropriate for peripheral administration without exceeding 10 mEq/hr. Choice A (31.25 mL/hr) may come from doubling time to 8 hours; choice B (50 mL/hr) could be from using 5 hours; choice D (125 mL/hr) might stem from halving time. Errors often involve misreading dilution volumes. Clinically, monitor ECG during potassium infusions in renal patients. A strategy is to confirm maximum rates per institutional protocols.

Question 6

A 40-year-old female (weight 75 kg) is admitted with severe nausea/vomiting and is found to have hypomagnesemia contributing to refractory hypokalemia. Past medical history includes GERD; renal function is normal. Labs: SCr 0.7 mg/dL, Na 136 mEq/L, K 3.1 mEq/L, Mg 1.1 mg/dL. The provider orders magnesium sulfate 2 g IV diluted in 100 mL to infuse over 1 hour. Calculate the mL/hr rate for the ordered infusion.

  1. 50 mL/hr
  2. 75 mL/hr
  3. 100 mL/hr (correct answer)
  4. 200 mL/hr

Explanation: The foundational pharmacy concept being tested is determining rates for magnesium infusions in electrolyte imbalances. The key patient-specific factor influencing the rate calculation is the patient's hypomagnesemia contributing to hypokalemia, requiring prompt but safe correction. The correct answer is 100 mL/hr, using total volume / infusion time (100 mL / 1 hr = 100 mL/hr), appropriate for 2 g over 1 hour. Choice A (50 mL/hr) may arise from doubling time; choice B (75 mL/hr) could be from partial misdivision; choice D (200 mL/hr) might result from halving time. Errors often involve time unit confusion. A pearl is to monitor reflexes and respiratory status during magnesium therapy. For similar tasks, confirm dilution guidelines to prevent phlebitis.

Question 7

A 41-year-old female (weight 80 kg) is admitted for acute pulmonary embolism and is started on an unfractionated heparin infusion. Past medical history includes obesity; renal function is normal. Labs: SCr 0.8 mg/dL, Na 139 mEq/L, K 4.3 mEq/L. The heparin bag is prepared as 25,000 units in 250 mL (100 units/mL), and the order is to infuse at 18 units/kg/hr. Calculate the infusion rate in mL/hr.

  1. 7.2 mL/hr
  2. 10.8 mL/hr
  3. 14.4 mL/hr (correct answer)
  4. 18 mL/hr

Explanation: The foundational pharmacy concept being tested is weight-based anticoagulant infusion rates for thrombotic events. The key patient-specific factor influencing the rate calculation is the patient's weight of 80 kg, critical for heparin dosing. The correct answer is 14.4 mL/hr, calculated as (18 units/kg/hr × 80 kg = 1440 units/hr) / 100 units/mL = 14.4 mL/hr. Choice A (7.2 mL/hr) may arise from halving; choice B (10.8 mL/hr) could be from 13.5 units/kg/hr; choice D (18 mL/hr) might be from weight misread as 100 kg. Distractors highlight arithmetic errors. A pearl is to monitor aPTT every 6 hours. Standardize concentration use across units for safety.

Question 8

A 38-year-old woman (weight 68 kg) is postoperative and requires continuous analgesia. The order is hydromorphone 0.2 mg/hr IV continuous infusion; the IV bag is prepared as hydromorphone 10 mg in 50 mL (0.2 mg/mL). Labs: serum creatinine 0.8 mg/dL, sodium 139 mEq/L, potassium 4.1 mEq/L, glucose 105 mg/dL; she is receiving 0.9% sodium chloride at 50 mL/hr and is not fluid overloaded. What is the appropriate infusion rate for this patient in mL/hr?

  1. 0.5 mL/hr
  2. 1 mL/hr (correct answer)
  3. 2 mL/hr
  4. 4 mL/hr

Explanation: This question tests calculation of continuous opioid infusion rates, requiring understanding of concentration-based calculations. The key factor is matching the ordered dose rate (0.2 mg/hr) with the prepared concentration (0.2 mg/mL). The correct answer of 1 mL/hr is calculated as 0.2 mg/hr ÷ 0.2 mg/mL = 1 mL/hr, providing the exact ordered dose. Option A (0.5 mL/hr) would deliver only half the ordered dose, option C (2 mL/hr) would double the dose, and option D (4 mL/hr) would quadruple it, all representing potentially dangerous dosing errors. For continuous infusions, always use the formula: Rate (mL/hr) = Desired dose (mg/hr) ÷ Concentration (mg/mL). When the ordered dose rate matches the concentration, the infusion rate will be 1 mL/hr, making verification straightforward.

Question 9

A 45-year-old female (weight 60 kg) is admitted for vomiting and diarrhea with moderate dehydration. Medical history includes type 2 diabetes; she is not in diabetic ketoacidosis. Labs: SCr 0.9 mg/dL, Na 134 mEq/L, K 3.9 mEq/L, glucose 168 mg/dL. The provider orders lactated Ringer's 2,000 mL IV to run over 20 hours. Determine the mL/hr rate for the patient's IV fluid order.

  1. 80 mL/hr
  2. 90 mL/hr
  3. 100 mL/hr (correct answer)
  4. 120 mL/hr

Explanation: The foundational pharmacy concept being tested is determining IV fluid rates for dehydration management in patients with comorbidities like diabetes. The key patient-specific factor influencing the rate calculation is the patient's weight and normal renal function, though the order is not weight-based here. The correct answer is 100 mL/hr, calculated using the formula total volume / infusion time (2000 mL / 20 hr = 100 mL/hr), ensuring gradual rehydration suitable for her condition. Choice A (80 mL/hr) might come from miscalculating time as 25 hours; choice B (90 mL/hr) could be from rounding errors or partial misdivision; choice D (120 mL/hr) may result from using 16.7 hours instead. Common misconceptions include confusing total volume with daily maintenance needs. Clinically, always confirm electrolyte balance during infusion in diabetic patients to avoid complications like hyperglycemia. A strategy for similar tasks is to use dimensional analysis to cross-check calculations.

Question 10

A 66-year-old male (weight 78 kg) with chronic kidney disease stage 3 is admitted for pneumonia and develops hypomagnesemia after diuretic therapy. Labs: SCr 2.0 mg/dL, Na 140 mEq/L, K 3.6 mEq/L, Mg 1.3 mg/dL. The provider orders magnesium sulfate 1 g IV in 50 mL to infuse over 2 hours. Determine the mL/hr rate for the medication infusion.

  1. 12.5 mL/hr
  2. 25 mL/hr (correct answer)
  3. 50 mL/hr
  4. 100 mL/hr

Explanation: The foundational pharmacy concept being tested is calculating slower infusion rates for magnesium in renal impairment. The key patient-specific factor influencing the rate calculation is the patient's chronic kidney disease stage 3, mandating extended infusion to avoid toxicity. The correct answer is 25 mL/hr, from total volume / infusion time (50 mL / 2 hr = 25 mL/hr), safe for 1 g in this setting. Choice A (12.5 mL/hr) may come from using 4 hours; choice C (50 mL/hr) could stem from 1 hour; choice D (100 mL/hr) might be from volume error. Common misconceptions include ignoring renal adjustments. Clinically, check serum magnesium post-infusion in CKD patients. A strategy is to use pump programming with alerts for rate limits.

Question 11

A 55-year-old male (weight 75 kg) is hospitalized for severe pain due to pancreatitis and is placed on a hydromorphone patient-controlled analgesia (PCA) with a basal infusion. Past medical history includes obstructive sleep apnea; renal function is normal. Labs: SCr 0.9 mg/dL, Na 137 mEq/L, K 4.1 mEq/L. The basal rate is ordered as hydromorphone 0.2 mg/hr, and the PCA concentration is 1 mg/mL. What is the basal infusion rate in mL/hr?

  1. 0.02 mL/hr
  2. 0.2 mL/hr (correct answer)
  3. 2 mL/hr
  4. 12 mL/hr

Explanation: The foundational pharmacy concept being tested is basal rate calculation for opioid PCAs in pain management. The key patient-specific factor influencing the rate calculation is the patient's obstructive sleep apnea, requiring low starting doses to avoid respiratory depression. The correct answer is 0.2 mL/hr, from basal dose (0.2 mg/hr) / concentration (1 mg/mL) = 0.2 mL/hr. Choice A (0.02 mL/hr) may come from misreading as 0.02 mg/hr; choice C (2 mL/hr) could be from 2 mg/hr; choice D (12 mL/hr) might stem from per-minute confusion. Errors often involve decimal placement. Clinically, assess sedation scores frequently. Use pump locks and protocols for opioid infusions.

Question 12

A 52-year-old man (weight 88 kg) is admitted for diabetic ketoacidosis and is started on a continuous regular insulin infusion. The order is regular insulin 0.1 units/kg/hr IV; pharmacy prepares 100 units in 100 mL of 0.9% sodium chloride (1 unit/mL). Labs: glucose 520 mg/dL, potassium 5.2 mEq/L, sodium 130 mEq/L, serum creatinine 1.3 mg/dL; he is receiving IV fluids and is clinically dehydrated. What is the appropriate infusion rate for this patient in mL/hr?

  1. 4.4 mL/hr
  2. 8.8 mL/hr (correct answer)
  3. 11 mL/hr
  4. 22 mL/hr

Explanation: This question tests insulin infusion calculations for diabetic ketoacidosis management, requiring weight-based dosing. The key patient-specific factor is the patient's weight (88 kg) for calculating units/hr. First, calculate the dose: 0.1 units/kg/hr × 88 kg = 8.8 units/hr. Then, using the 1 unit/mL concentration: 8.8 units/hr ÷ 1 unit/mL = 8.8 mL/hr. Option A (4.4 mL/hr) represents half the correct dose, option C (11 mL/hr) overestimates by 25%, and option D (22 mL/hr) would deliver 2.5 times the ordered dose. For DKA insulin infusions, the standard initial rate is 0.1 units/kg/hr, with adjustments based on glucose decline (target 50-75 mg/dL/hr). Always use a dedicated line for insulin to prevent dosing errors from line flushes.

Question 13

A 68-year-old male (weight 80 kg) presents to the emergency department with dizziness and poor oral intake for 2 days and is assessed as dehydrated. Past medical history includes hypertension and chronic kidney disease stage 3. Labs: SCr 1.8 mg/dL, Na 148 mEq/L, K 4.0 mEq/L, glucose 112 mg/dL. He has dry mucous membranes and low urine output; an order is placed for 0.9% sodium chloride 1,000 mL IV to infuse over 8 hours. Calculate the mL/hr rate for the ordered IV fluid.

  1. 100 mL/hr
  2. 125 mL/hr (correct answer)
  3. 62.5 mL/hr
  4. 150 mL/hr

Explanation: The foundational pharmacy concept being tested is the calculation of intravenous infusion rates to ensure safe and effective fluid administration. The key patient-specific factor influencing the rate calculation is the patient's chronic kidney disease stage 3 and elevated serum creatinine, requiring cautious fluid replacement to prevent overload. The correct answer is 125 mL/hr, as the formula for infusion rate is total volume divided by infusion time (1000 mL / 8 hr = 125 mL/hr), providing appropriate rehydration without exceeding renal capacity. Choice A (100 mL/hr) may result from incorrectly using 10 hours instead of 8; choice C (62.5 mL/hr) could stem from doubling the time to 16 hours; choice D (150 mL/hr) might arise from shortening the time to about 6.7 hours. These errors often occur from misreading the order or arithmetic mistakes. A transferable clinical pearl is to always verify the ordered volume and duration against the patient's clinical status, such as renal function, before setting the pump. Additionally, monitor vital signs and urine output during infusion to adjust as needed in compromised patients.

Question 14

A 50-year-old male (weight 70 kg) is admitted with acute coronary syndrome and is started on a nitroglycerin infusion for ongoing chest pain. Past medical history includes hypertension and hyperlipidemia. Labs: SCr 1.0 mg/dL, Na 140 mEq/L, K 4.0 mEq/L. The nitroglycerin infusion concentration is 50 mg in 250 mL (200 mcg/mL), and the order is to start at 20 mcg/min. Determine the infusion rate in mL/hr.

  1. 3 mL/hr
  2. 6 mL/hr (correct answer)
  3. 12 mL/hr
  4. 24 mL/hr

Explanation: The foundational pharmacy concept being tested is converting vasoactive doses to infusion rates for angina control. The key patient-specific factor influencing the rate calculation is the patient's ongoing chest pain, requiring titration. The correct answer is 6 mL/hr, from (20 mcg/min × 60 min/hr = 1200 mcg/hr) / 200 mcg/mL = 6 mL/hr. Choice A (3 mL/hr) may come from 10 mcg/min; choice C (12 mL/hr) could be doubling; choice D (24 mL/hr) might stem from concentration as 50 mcg/mL. Common errors include minute-to-hour conversion. Clinically, monitor blood pressure continuously. Calculate mcg/hr first then divide by concentration.

Question 15

A 63-year-old male (weight 110 kg) is admitted with acute decompensated heart failure and is started on a furosemide continuous infusion after inadequate response to bolus dosing. Past medical history includes chronic kidney disease stage 3. Labs: SCr 2.1 mg/dL, Na 132 mEq/L, K 4.7 mEq/L. The infusion bag contains furosemide 100 mg in 100 mL (1 mg/mL), and the order is to infuse at 10 mg/hr. Calculate the mL/hr rate.

  1. 5 mL/hr
  2. 10 mL/hr (correct answer)
  3. 20 mL/hr
  4. 40 mL/hr

Explanation: The foundational pharmacy concept being tested is rate calculation for loop diuretic infusions in fluid overload states. The key patient-specific factor influencing the rate calculation is the patient's chronic kidney disease stage 3, affecting response but not direct calculation. The correct answer is 10 mL/hr, as ordered dose (10 mg/hr) / concentration (1 mg/mL) = 10 mL/hr, suitable for decompensated heart failure. Choice A (5 mL/hr) may come from 5 mg/hr; choice C (20 mL/hr) could be doubling; choice D (40 mL/hr) might stem from concentration misread. Distractors highlight dose-concentration confusion. Clinically, track urine output and electrolytes hourly. Confirm bag concentration before initiating infusions.

Question 16

A 34-year-old female (weight 70 kg) is in the ICU for status epilepticus and is placed on a continuous midazolam infusion. Past medical history includes epilepsy; renal function is normal. Labs: SCr 0.8 mg/dL, Na 138 mEq/L, K 4.0 mEq/L. Midazolam infusion is prepared as 100 mg in 100 mL (1 mg/mL), and the order is 0.1 mg/kg/hr. What is the appropriate infusion rate in mL/hr?

  1. 3.5 mL/hr
  2. 7 mL/hr (correct answer)
  3. 10 mL/hr
  4. 14 mL/hr

Explanation: The foundational pharmacy concept being tested is continuous infusion rate determination for benzodiazepines in seizure management. The key patient-specific factor influencing the rate calculation is the patient's weight of 70 kg, essential for dosing accuracy. The correct answer is 7 mL/hr, from dose (0.1 mg/kg/hr × 70 kg = 7 mg/hr) / concentration (1 mg/mL) = 7 mL/hr. Choice A (3.5 mL/hr) may arise from halving weight; choice C (10 mL/hr) could be from using 0.14 mg/kg/hr; choice D (14 mL/hr) might result from doubling dose. Common errors include forgetting weight adjustment. A pearl is to monitor respiratory depression in epilepsy patients on midazolam. Use step-by-step dimensional analysis for complex units.

Question 17

A 23-year-old male (weight 72 kg) is treated in the hospital for pyelonephritis. He has no significant past medical history. Labs: SCr 0.9 mg/dL, Na 139 mEq/L, K 4.0 mEq/L. The provider orders ceftriaxone 2 g IV in 100 mL to infuse over 30 minutes. What is the appropriate infusion rate in mL/hr?

  1. 100 mL/hr
  2. 150 mL/hr
  3. 200 mL/hr (correct answer)
  4. 300 mL/hr

Explanation: The foundational pharmacy concept being tested is rapid infusion rate calculation for beta-lactam antibiotics in acute infections. The key patient-specific factor influencing the rate calculation is the patient's young age and normal renal function, allowing standard rates. The correct answer is 200 mL/hr, calculated as total volume / time in hours (100 mL / 0.5 hr = 200 mL/hr), with time = 30 / 60 = 0.5 hr. Choice A (100 mL/hr) may come from using 1 hour; choice B (150 mL/hr) could be from volume misread; choice D (300 mL/hr) might result from 20-minute infusion. Common errors include forgetting to convert minutes to hours. Clinically, ensure compatibility with IV lines for short infusions. A strategy is to verify by calculating total time needed at proposed rate.

Question 18

A 30-year-old male (weight 90 kg) is treated in the emergency department for heat exhaustion with dehydration. He has no significant past medical history. Labs: SCr 1.0 mg/dL, Na 142 mEq/L, K 4.1 mEq/L, glucose 98 mg/dL. The provider orders 0.9% sodium chloride 500 mL IV to infuse over 2 hours using tubing with a drop factor of 15 gtt/mL. Determine the drops/min rate for the patient's IV fluid order.

  1. 31 gtt/min
  2. 63 gtt/min (correct answer)
  3. 75 gtt/min
  4. 125 gtt/min

Explanation: The foundational pharmacy concept being tested is converting IV infusion rates to drops per minute using tubing drop factors. The key patient-specific factor influencing the rate calculation is the patient's weight, though not directly used, with normal renal function allowing standard rehydration. The correct answer is 63 gtt/min, approximated from the formula (total volume × drop factor) / total minutes = (500 mL × 15 gtt/mL) / 120 min = 7500 / 120 = 62.5 gtt/min, rounded to 63 for practical administration. Choice A (31 gtt/min) may result from halving the volume or doubling time; choice C (75 gtt/min) could be from using 10 gtt/mL; choice D (125 gtt/min) might stem from omitting division by time. Common errors include forgetting to convert hours to minutes. Clinically, recalibrate pumps if switching tubing to maintain accuracy. A strategy is to calculate both mL/hr first (250 mL/hr) then convert to verify drops.

Question 19

A 67-year-old man (weight 78 kg) presents to the emergency department with dizziness and poor oral intake for 3 days; exam suggests dehydration (dry mucous membranes) and he is ordered 0.9% sodium chloride 1,000 mL IV to infuse over 8 hours. Pertinent labs: serum creatinine 1.6 mg/dL, sodium 148 mEq/L, potassium 4.1 mEq/L, glucose 110 mg/dL. He has a history of hypertension and chronic kidney disease stage 3 and is currently not tolerating oral fluids. Calculate the mL/hr rate for the ordered IV fluid.

  1. 100 mL/hr
  2. 125 mL/hr (correct answer)
  3. 150 mL/hr
  4. 250 mL/hr

Explanation: This question tests the fundamental skill of calculating IV infusion rates using the formula: Rate (mL/hr) = Total Volume (mL) ÷ Time (hr). The key patient-specific factor here is the 8-hour infusion time for 1,000 mL of fluid in a dehydrated patient with chronic kidney disease. The correct answer of 125 mL/hr is calculated as 1,000 mL ÷ 8 hours = 125 mL/hr, which provides appropriate rehydration without overwhelming the patient's compromised renal function. Option A (100 mL/hr) represents dividing by 10 hours instead of 8, option C (150 mL/hr) might result from dividing by 6.67 hours, and option D (250 mL/hr) incorrectly divides by 4 hours. When calculating infusion rates, always double-check the time units and ensure they match the desired rate units (mL/hr requires time in hours, not minutes).

Question 20

A 54-year-old woman (weight 62 kg) is admitted for weakness and palpitations; ECG shows frequent premature ventricular contractions. Labs: potassium 2.9 mEq/L, magnesium 1.7 mg/dL, serum creatinine 0.9 mg/dL, sodium 138 mEq/L, glucose 96 mg/dL. The provider orders potassium chloride 40 mEq in 250 mL of 0.9% sodium chloride IV to infuse over 4 hours via peripheral line; the patient is mildly volume depleted but hemodynamically stable. What is the appropriate infusion rate for this patient in mL/hr?

  1. 31.25 mL/hr
  2. 62.5 mL/hr (correct answer)
  3. 83.3 mL/hr
  4. 125 mL/hr

Explanation: This question evaluates understanding of potassium infusion rate calculations and safety parameters for peripheral IV administration. The key patient-specific factor is the peripheral line administration of potassium, which has maximum concentration and rate restrictions to prevent phlebitis and cardiac complications. The correct answer of 62.5 mL/hr is calculated as 250 mL ÷ 4 hours = 62.5 mL/hr, delivering potassium at 10 mEq/hr (40 mEq ÷ 4 hours), which is within the safe limit of 10 mEq/hr for peripheral administration. Option A (31.25 mL/hr) represents dividing by 8 hours, option C (83.3 mL/hr) divides by 3 hours, and option D (125 mL/hr) divides by 2 hours—the latter two would exceed safe peripheral potassium infusion rates. Remember that peripheral potassium should not exceed 10 mEq/hr, while central line administration can go up to 20 mEq/hr in monitored settings.