NR 226: Medication Dosage Calculations Review

This section provides a comprehensive review of common medication dosage calculations for oral, subcutaneous, and intravenous administration. Each example demonstrates the use of dimensional analysis to determine the correct dosage volume, emphasizing safety and accuracy in nursing practice.

Question 1

The patient has been prescribed cephalexin (Keflex) 325 mg orally. The available solution contains 250 mg per 2 mL. Using dimensional analysis, the nurse calculates that 2.6 mL should be administered.

Dimensional Analysis:

2 mL325 mg=250 mgx\frac{2 \, \text{mL}}{325 \, \text{mg}} = \frac{250 \, \text{mg}}{x}

Calculated Volume: 2.6 mL

Question 2

For amoxicillin (Amoxil) 2.4 g orally, with a concentration of 600 mg per 10 mL, the required volume is calculated as 40 mL.

Dimensional Analysis:

10 mL600 mg=x mL2400 mg\frac{10 \, \text{mL}}{600 \, \text{mg}} = \frac{x \, \text{mL}}{2400 \, \text{mg}}

Calculated Volume: 40 mL

Question 3

A patient requires diphenhydramine HCl (Benadryl) 37.5 mg orally, with 12.5 mg per 10 mL available. The nurse should administer 30 mL.

Dimensional Analysis:

10 mL12.5 mg=x mL37.5 mg\frac{10 \, \text{mL}}{12.5 \, \text{mg}} = \frac{x \, \text{mL}}{37.5 \, \text{mg}}

Calculated Volume: 30 mL

Question 4

The order is for potassium chloride (K-Lor) 60 mEq orally, with a concentration of 40 mEq per 10 mL. The nurse calculates 15 mL for administration.

Dimensional Analysis:

10 mL40 mEq=x mL60 mEq\frac{10 \, \text{mL}}{40 \, \text{mEq}} = \frac{x \, \text{mL}}{60 \, \text{mEq}}

Calculated Volume: 15 mL

Question 5

A patient is prescribed gabapentin (Neurontin) 275 mg orally, with an available concentration of 250 mg per 10 mL. The nurse should administer 11 mL.

Dimensional Analysis:

10 mL250 mg=x mL275 mg\frac{10 \, \text{mL}}{250 \, \text{mg}} = \frac{x \, \text{mL}}{275 \, \text{mg}}

Calculated Volume: 11 mL

Oral Tablet Dosages

The following table summarizes calculations for medications available in tablet form:

Weight-Based and Subcutaneous Medications

Question 13

For cyclosporine (Neoral) 4 mg/kg/day, a patient weighing 162 lb requires a daily dose of 295 mg.

Dimensional Analysis:

4 mg/kg×162 lb2.2 lb/kg=294.5 mg (rounded to 295 mg)4 \, \text{mg/kg} \times \frac{162 \, \text{lb}}{2.2 \, \text{lb/kg}} = 294.5 \, \text{mg (rounded to 295 mg)}

Question 15

The patient has an order for atropine (AtroPen) 450 mcg subcutaneously, with a concentration of 0.5 mg per 0.7 mL. The calculated volume is 0.6 mL.

Question 16

Enoxaparin (Lovenox) 1 mg/kg subcutaneously, patient weight 180 lb, requires 0.8 mL.

Question 18

Cyanocobalamin (Vitamin B12) 70 mcg subcutaneously, with 0.1 mg/mL available, is administered at 0.7 mL.

IV and IM Medications

Key Points

• Dimensional analysis is essential for safe medication administration, converting units accurately.

• Tablet, oral liquid, subcutaneous, IV, and IM medications each require careful calculation.

• Always verify patient weight and medication concentration before administration to prevent dosing errors.

References

American Nurses Association. (2021). Nursing: Scope and standards of practice (4th ed.). ANA.

Timby, B. K., & Smith, N. E. (2020). Fundamentals of nursing: Concepts, process, and practice (10th ed.). F.A. Davis.

NR 226 Quiz 1

McCuistion, L. E., & Hayes, C. (2021). Pharmacology for nursing care (10th ed.). Elsevier.