NAPLEX® Review Question of the Week: Leveraging Levophed
NP is a 54-year-old female who is receiving a Levophed drip (4mg/250mL) in the ICU. The order states that the drip can be titrated to a maximum dose of 0.2mcg/kg/minute.
Labs/Vitals
Wt: 141 lbs
BP: 85/63 mmHg
HR: 95 bpm
MAP: 60 mmHg
SCr: 0.9 mg/dL
pH: 7
Considering you want to run the drip at the maximum dose, what is the maximum infusion rate (mL/hr) at which the drip can be run?
A. 105 mL/hr
B. 48 mL/hr
C. 8 mL/hr
D. 24 mL/hr
Answer with Rationale
Foundational knowledge for pharmacy practice makes up 25% of the NAPLEX, and a large portion of this is pharmaceutical calculations. In order to prepare, it is important to understand how to properly calculate rates of administration. The rate of administration specifies how much volume of a drug a patient will receive over a period of time. This depends upon what dose and concentration of the drug is available. When tackling these problems, set up proportions and make sure that all units cancel if they are not desired in the final answer. If the target infusion rate requires units in mL/hr, ensure that volume is in the numerator and time is in the denominator from the start. Be attentive to the units of measure for every value and make conversions accordingly.
Answer A is incorrect. If your final answer is 105 mL/hr, it is likely you forgot to convert the patient’s weight from lbs to kg.
Answer B is correct. Refer to the proportions below.
Start by taking the maximum dose of 0.2 mcg/kg/min and multiply by the patient’s weight to get the patient-specific rate of administration.
0.2 mcg/kg/min x 141 lbs x 1kg/2.2 lbs = 12.8 mcg/min
The first fraction below is the drug concentration. Notice how the volume (250mL) is in the numerator in order to achieve a final desired rate of mL/hr. The second fraction converts the units from milligrams to micrograms. This conversion is required in order to multiply by the patient-specific rate that was calculated in the first step and is represented by the third fraction. The fourth and final fraction is required to convert from minutes to hours.
250 mL x 1 mg x 12.8 mcg x 60 min = 48 mL/hr
4 mg 1000 mcg 1 min 1 hr
Answer C is incorrect. This is not a feasible answer.
Answer D is incorrect. This would be correct if the bag was compounded with 8mg of norepinephrine per 250mL. Sometimes in patients who are fluid restricted, various medication piggybacks can be maximally concentrated to decrease the total "hidden" fluids that can significantly contribute to a patient's overall fluid status.
Brand/Generic: norepinephrine bitartrate (Levophed)
NAPLEX Content Domains Covered:
1.C.3 - Rates of administration
1.C.4 - Dose conversions
Dr. Christopher M. Bland is the Albert W. Jowdy Professor in Pharmacy Care at the University of Georgia College of Pharmacy at the Southeast GA campus in Savannah, GA. Dr. Bland has nearly 25 years of academic and clinical experience both in the inpatient and community patient care settings. He is a Fellow of both the Infectious Diseases Society of America as well as the American College of Clinical Pharmacy and has been named Teacher of the Year at the University of Georgia College of Pharmacy. He is co-author of the book "InteGREAT: A Guidebook for Creating Great Healthcare Teams."
He is co-founder of the Southeastern Research Group Endeavor, SERGE-45, with nearly 100 practitioners across 14 states involved. Dr. Bland serves as Associate Editor for the NAPLEX Review Guide 4th edition as well as upcoming 5th edition, as well as the Editor-In-Chief for the Question of the Week. He has provided hundreds of hours in live, interactive NAPLEX reviews for more than 10 Colleges/Schools of Pharmacy over the course of his career.
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