VATI RN Maternal Newborn Assessment Practice Exam

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When administering methotrexate 1 mg/kg IM to a client weighing 110 lbs, how many mL should the nurse administer if the available concentration is 25 mg/mL?

1 mL. 2 mL. 4 mL. 5 mL.

Correct Answer:

2 mL.

Explanation:

To determine how many mL of methotrexate to administer, first, convert the client's weight from pounds to kilograms, as the dosage is given in mg/kg. The conversion factor is approximately 2.2 lbs per kg. Thus, a client weighing 110 lbs would weigh about 50 kg (110 lbs ÷ 2.2 lbs/kg). The dosage calculation begins by multiplying the weight in kg by the required dose of methotrexate: 1 mg/kg × 50 kg = 50 mg. Next, to find out how many mL this amount equates to with the available concentration of 25 mg/mL, divide the total mg needed by the concentration: 50 mg ÷ 25 mg/mL = 2 mL. Administering 2 mL achieves the required dosage of 50 mg for this client. Therefore, the correct amount to administer is 2 mL.

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