Dosage Calculation RN Adult Medical-Surgical Nursing Practice 3.2 | Answers & Explanations

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Dosage Calculation RN Adult Med-Surg
Practice 3.2 — Answers with Explanations

1. Cefazolin 250 mg IM

 Available: 225 mg/mL
 Calculation: ( \text{Dose needed} \div \text{Concentration} = 250 \div 225 = 1.11
\approx 1.1 , \text{mL} )
 Explanation: The nurse calculates the volume to deliver the exact dose based on the
reconstituted concentration. Round to the nearest tenth.



2. Dextrose 5% (D5W) 250 mL IV over 2 hr

 Calculation: ( 250 \text{ mL} \div 2 \text{ hr} = 125 \text{ mL/hr} )
 Explanation: IV pump rate is total volume divided by infusion time in hours.



3. Metoclopramide 10 mg PO

 Available: 5 mg tablets
 Calculation: ( 10 \div 5 = 2 ) tablets
 Explanation: Divide the ordered dose by available strength to find number of tablets.



4. Cefazolin 500 mg IM every 12 hr

 Available: 330 mg/mL
 Calculation: ( 500 \div 330 = 1.515 \approx 1.5 , \text{mL} )
 Explanation: Calculate mL based on available concentration; round to the nearest tenth.



5. Prescription Clarification

 Example: Carvedilol 6.25 mg BID, hold for apical pulse < 50 bpm




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 Explanation: Nurse should clarify if the client’s pulse is borderline to prevent
bradycardia or adverse events.



6. 0.9% NaCl 1,000 mL IV at 125 mL/hr, drop factor 15 gtt/mL

 Calculation: ( 125 \text{ mL/hr} \times 15 \text{ gtt/mL} \div 60 \text{ min/hr} = 31.25
\approx 31 \text{ gtt/min} )
 Explanation: Multiply rate by drop factor, divide by 60 to convert to gtt/min.



7. Methylprednisolone 0.05 g IM

 Available: 80 mg/mL
 Calculation: Convert 0.05 g to mg: ( 0.05 \times 1000 = 50 \text{ mg} )
( 50 \div 80 = 0.625 \approx 0.63 , \text{mL} )
 Explanation: Always convert grams to mg to match vial concentration.



8. Methadone 0.1 mg/kg IV, client 104 lb

 Convert weight to kg: ( 104 \div 2.2 = 47.27 \text{ kg} )
 Dose: ( 47.27 \times 0.1 = 4.73 \text{ mg} )
 Volume: ( 4.73 \div 10 = 0.473 \approx 0.47 , \text{mL} )
 Explanation: Convert lbs to kg; multiply by dose/kg; divide by concentration.



9. Phenytoin 15 mg/kg IV, client 154 lb

 Weight in kg: ( 154 \div 2.2 = 70 \text{ kg} )
 Dose: ( 70 \times 15 = 1050 \text{ mg} )
 Volume: ( 1050 \div 50 = 21 \text{ mL} )
 Explanation: Convert weight to kg, calculate total mg, then mL from concentration.



10. Phenytoin 5 mg/kg/day PO divided every 8 hr, client 132 lb

 Weight in kg: ( 132 \div 2.2 = 60 \text{ kg} )
 Total daily dose: ( 60 \times 5 = 300 \text{ mg/day} )
 Per dose (divided 3x/day): ( 300 \div 3 = 100 \text{ mg} ) → 1 capsule
 Explanation: Divide total daily dose by frequency to determine per-dose amount.




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