NAPLEX Question of the Week: What dose it is anyway?

Is dosing on the exam? Most definitely.
NAPLEX Question of the Week: What dose it is anyway?
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MA is a 30 year old female (5’4”, 55 kg) who presents to the emergency department with pain and swelling in her right leg after finishing up a weekend road trip. She also has some increased shortness of breath but otherwise is stable. Duplex ultrasonography shows a distal deep vein thrombosis (DVT) in the patient’s right leg and CT pulmonary angiography shows presence of a pulmonary embolism (PE). The resident physician wishes to initiate enoxaparin therapy as they will be admitted to the medicine ward. 
PMH:
T2DM

Medications:
Ethinyl Estradiol and Drospirenone 1 tab PO QD
Metformin 500 mg PO BID
Vitals and labs:
HR:115 BPM
RR: 12 BPM
Temp: 98.7*F
BP: 110/75 mmHg
Na: 139 mEq/L
K: 4.2 mEq/L
Plt: 200,000/uL
Hgb: 13.5 g/dL
Hct: 43%
D-dimer: 1200 ng/mL
BG: 125 mg/dL
SCr: 0.8 mg/dL
What is the correct enoxaparin dose for this patient?

A. 80 mg SQ daily

B. 60 mg SQ daily

C. 40 mg SQ daily

D. 30 mg SQ daily

DVT is an urgent condition that can progress to a PE and subsequently death if left untreated. Patient symptoms may include unilateral swelling, redness, or tenderness and imaging such as duplex ultrasonography may be used to confirm the presence of a DVT. Factors that may increase a patient’s risk of developing a DVT include immobility, cancer, history of smoking, use of hormonal contraceptives, diabetes, and more. MA was on oral contraceptives so unless a specific other factor was identified for the DVT, alternative contraception should be likely undertaken. DVT pharmacological treatment options include the use of direct oral anticoagulants, vitamin K antagonists, unfractionated heparin, or low molecular weight heparins.
Enoxaparin is a low molecular weight heparin used for the prevention and treatment of DVT. It’s given subcutaneously and requires renal dose adjustments depending on the patient’s creatinine clearance (CrCl). Enoxaparin is contraindicated in patients with active bleeding and a history of or active heparin-induced thrombocytopenia (HIT). Monitor patient hemoglobin, platelet count, and hematocrit throughout treatment as well as signs and symptoms of bleeding.
To determine this patient’s enoxaparin dose, their CrCl should be calculated.
Begin by finding the patient’s ideal body weight (IBW).
IBW (for women) = 45.5 + (2.3 x inches over 5 feet)
IBW = 45.5 + (2.3 x 4)
IBW = 54.7 kg
MA's actual body weight and ideal are essentially the same. Use the IBW to calculate the patient’s CrCl with the Cockcroft-Gault equation.
CrCl =     (140-age) x weight in kg) 
                 ——————————     x 0.85 if female
                    (SCr in mg/dL x 72)
CrCl =      (140-30) x 54.7)
                ———————   x 0.85
                       (0.8 x 72)
CrCl = 88.79 mL/min
Answer A is correct. The recommended enoxaparin dose for DVT treatment in patients with a CrCl greater than or equal to 30 mL/min is 1 mg/kg SQ Q12H or 1.5 mg/kg SQ QD. 1.5mg X 54.7kg = 82mg. Therefore the closest syringe that matches this would be 80mg. The FDA-label specifies this dose is for inpatients requiring treatment but off-label this is sometimes used to allow once dose daily. 
Answer B is incorrect. 1 mg/kg SQ QD is the recommended enoxaparin dose for DVT treatment in patients with a CrCl less than 30 mL/min. The closest syringe available to this is the 60mg syringe. However this patient's renal function is excellent so 60mg SQ BID would be most appropriate. 
Answer C is incorrect. 40 mg SQ QD is the recommended enoxaparin dose for DVT prophylaxis in patients with a CrCl greater than or equal to 30 mL/min. Our patient requires active treatment. 
Answer D is incorrect. 30 mg SQ QD is the recommended enoxaparin dose for DVT prophylaxis in patients with a CrCl less than 30 mL/min. Our patient requires active treatment. 
Brand/Generics covered: Enoxaparin (Lovenox), Ethinyl Estradiol and Drospirenone (Yasmin), Metformin (Glucophage)
NAPLEX Competencies Covered:
Area 3 - Develop or Manage Treatment Plans
3.4 - Drug dosing or dosing adjustments; duration of therapy
Area 4 - Perform Calculations 
4.1 - Patient Parameters or laboratory measures

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