NAPLEX Question of the Week: Thryoid Threat

This week's question tackles thyroid disorders.
NAPLEX Question of the Week: Thryoid Threat

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SP is a 53-year-old male (167 cm, 110 kg) that presents to your ambulatory care clinic this morning for a routine checkup. During his visit, he mentions he’s recently had some unexpected weight gain, drier skin than usual, and constipation.

Social History: No alcohol use. History of smoking 1 ppd for 20 years.

Allergies: NKDA

PMH: HTN, hyperlipidemia, HFrEF, obesity, MI (5 years prior), CAD

Current Medication List:

  • Entresto 97/103 mg orally BID
  • Carvedilol 25 mg orally BID
  • Spironolactone 25 mg orally daily
  • Dapagliflozin 10 mg orally daily
  • Atorvastatin 40 mg orally daily
  • Aspirin 81 mg orally daily

Vitals and lab results:

HR: 76 BPM

RR: 18 BPM

BP: 125/77 mmHg

TSH: 11 mIU/L (ref: 0.4-4.9 mIU/L)

T4: 4 mcg/dL (ref: 5-11 mcg/dL)

TC: 215 mg/dL

LDL: 185 mg/dL

HDL: 30 mg/dL

Triglycerides: 132 mg/dL

Which medication regimen would be appropriate for SP at this time?

 A. Initiate Synthroid 137 mcg daily

B. Initiate Levoxyl 25 mcg daily

C. Initiate Armour Thyroid 30 mg daily

D. Initiate Tapazole 5 mg daily

Answer with Rationale

Thyroid disorders are diagnosed via analysis of TSH levels and review of patient symptoms. Hypothyroidism is characterized by increased TSH, decreased T3 and T4, and a variety of symptoms including weight gain, cold intolerance, constipation, hair loss, and dry skin. Medication therapy for hypothyroidism should be initiated when TSH > 10mIU/L.

Levothyroxine (brand names: Tirosint, Synthroid, Levoxyl) is a synthetic form of T4 that is recommended as the agent of choice in patients with hypothyroidism. It has specific initial dosing instructions depending on patient age and presence of coronary heart disease (CHD). Patients less than 60 years old with no presence of CHD should be initiated on 1.6 mcg/kg/day and patients greater than 60 years old with no presence of CHD should be initiated on 25-50 mcg once daily. Patients of any age with CHD should be initiated on 12.5-50 mcg once daily.

There are many different strengths of levothyroxine due to need for titration for each individual patient. These are in different colors so that knowing these colors can help patients identify which tablet they are taking. In addition, caution should be taken if switching from one brand to another as these are not necessarily bioequivalent. In general, maintaining the same brand is recommended for consistency. 

Answer A is incorrect: If this patient did not have CHD, 137 mcg would be the recommended initial starting dose (1.6 mcg/kg/day) of levothyroxine (Levoxyl) due to his age based on his ideal body weight of 86kg. However, in the presence of CHD 137 mcg is too high of an initial dose and would not be appropriate.

Answer B is correct: Because of this patient’s CHD, the recommended initial starting dose of levothyroxine is 12.5-50 mcg daily with plans to titrate up based on symptoms and TSH levels.

Answer C is incorrect:  Armour Thyroid (desiccated thyroid hormone) is not recommended for treatment of primary or secondary hypothyroidism but is available as an alternative to guideline recommended therapies. While not a concern for this patient, Armour Thyroid should also be avoided in pregnancy. It is also important to note that desiccated thyroid hormone strength may be listed in grains or milligrams depending on the formulation and manufacturer, and that the dosing recommendations are based on general equivalencies of 1 grain = 60 mg or 65 mg.

Answer D is incorrect: Methimazole (Tapazole) is an option for the treatment of hyperthyroidism which is characterized by decreased TSH and increased T3 and T4 levels. Common symptoms of hyperthyroidism include weight loss, shaking, and sweating. Methimazole works by blocking the synthesis of T3 and should not be used in the treatment of hypothyroidism.

Brand/Generics covered: Levothyroxine (Tirosint, Levoxyl, Synthroid), Methimazole (Tapazole), Sacubitril/Valsartan (Entresto), Carvedilol (Coreg), Spironolactone (Aldactone), Dapagliflozin (Farxiga), Atorvastatin (Lipitor)

Naplex Competencies:

Area 1 - Obtain, Interpret, or Assess Data, Medical or Patient Information

1.1 - From instruments, screening tools, laboratory, genomic or genetic information, or diagnostic findings

1.5 - Signs or symptoms of medical conditions, healthy physiology, etiology of diseases, or pathophysiology

Area 2 - Identify Drug Characteristics

2.2 - Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied

Area 3 - Develop or Manage Treatment Plans

3.4 - Drug dosing or dosage adjustments; duration of therapy

3.11 - Evidence-based practice

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