Clinical Case Segment

Vignette:

History of Present Illness: A 75-year-old White woman presents to the ambulatory care clinic for initial management of hypothyroidism. She was diagnosed with hypothyroidism about a week ago. Since then, she has not started any new medications. She reports constipation, feeling cold, and chronic fatigue. She reports adherence to all current medications.

Medical History: Newly diagnosed hypothyroidism, atrial fibrillation for 15 years, myocardial infarction 25 years ago, hypertension for 25 years, osteoarthritis for 10 years, gastroesophageal reflux disease for 8 years

Social History: Married with two children; son has type 2 diabetes and hypertension; daughter has Hashimoto thyroiditis. Insurance: Medicare. Denies use of tobacco and illicit drugs. Drinks 1 glass of red wine daily

Current Medications: Warfarin 5 mg 1 tablet orally Monday, Wednesday, Friday and ½ tablet Sunday, Tuesday, Thursday, Saturday; metoprolol tartrate 50 mg orally twice daily; lisinopril 20 mg orally daily; atorvastatin 40 mg orally daily; ibuprofen 200 mg orally twice daily as needed; calcium carbonate 1000 mg orally twice daily as needed

Allergies: NKDA

Vital Signs: Blood pressure 118/76 mm Hg, heart rate 88 beats/minute, respiratory rate 16 breaths/minute, temperature 36.7°C, weight 45 kg, height 152 cm

Laboratory Values: Na 138 mEq/L (138 mmol/L), K 3.9 mEq/L (3.9 mmol/L), Cl 101 mEq/L (101 mmol/L), HCO₃ 22 mEq/L (22 mmol/L), BUN 28 mg/dL (10 mmol/L), SCr 1.2 mg/dL (106 micromoles/L), eGFR 35 mL/minute/1.73 m², glucose 72 mg/dL (4 mmol/L), calcium 9.2 mg/dL (2.3 mmol/L), magnesium 1.8 mEq/L (0.9 mmol/L), total protein 6.6 g/dL (66 g/L), albumin 3.6 g/dL (36 g/L), Hgb 12.5 g/dL (125 g/L), Hct 39%, INR 2.4, thyrotropin 6.8 mIU/L, free T₄ 0.25 ng/dL (3.2 pmol/L)

Procedure Data: ECG – atrial fibrillation

Question 1

Which of the patient’s medications may decrease the absorption of levothyroxine?

1. Calcium carbonate.
2. Ibuprofen.
3. Metoprolol tartrate.
4. Warfarin.

Answer: 1. Calcium carbonate

Rationale: Answer 1 is correct. Calcium salts may decrease the absorption of levothyroxine. These medications must be administered at least 4 hours apart. Answers 2 and 3 have no clinically significant interactions with levothyroxine. Levothyroxine may interfere with warfarin (Answer 4); however, warfarin does not decrease the absorption of levothyroxine.

Citations:

1. Garber J, Cobin R, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract 2012;18:988-1028.

2. Levoxyl [package insert]. King Pharmaceuticals, 2007.

Question 2

The patient needs to start antiarrhythmic therapy for her atrial fibrillation. Which medication may influence the patient’s thyrotropin concentration?

1. Amiodarone.
2. Dronedarone.
3. Flecainide.
4. Propafenone.

Answer: 1. Amiodarone

Rationale: Answer 1, amiodarone, may drastically affect thyrotropin concentrations. Amiodarone contains iodine molecules, which may cause hypo- or hyperthyroidism. Amiodarone also may decrease the conversion of T₄ to T₃ (active form of thyroid hormone). Therefore, even though there is no direct interaction between levothyroxine and amiodarone, adding amiodarone to this patient’s drug regimen may affect her thyrotropin concentrations. Answers 2, 3, and 4 do not significantly affect thyrotropin concentrations.

Citation: Levoxyl [package insert]. King Pharmaceuticals, 2007.

Question 3

Which initial medication and dose is appropriate for this patient’s hypothyroidism?

1. Desiccated thyroid 30 mg orally daily.
2. Desiccated thyroid 45 mcg orally daily.
3. Levothyroxine 25 mcg orally daily.
4. Levothyroxine 50 mcg orally daily.

Answer: 3.      Levothyroxine 25 mcg orally daily

Rationale: Answer 3 is correct. Older adult patients absorb less levothyroxine because of decreased lean body muscle. Guidelines recommend that patients older than 50–60 years start at doses no higher than 50 mcg of levothyroxine. Furthermore, this patient has heart disease, placing her at increased risk of cardiovascular complications if she has excess thyroid hormone. The starting levothyroxine dose for those with cardiovascular disease is 12.5–25 mcg orally daily. For these reasons, Answer 4 is incorrect. Answers 1 and 2 are incorrect because desiccated thyroid is not the agent of choice for hypothyroidism, given the risk of thyrotoxicosis and limited studies.

Citation: Garber J, Cobin R, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract 2012;18:988-1028.

Question 4

Regardless of what you recommended, the patient was initiated on levothyroxine 25 mcg orally daily. In 8 weeks, the patient returns for her laboratory tests. Her thyrotropin concentration is 6.3 mIU/L. The patient states she has been adherent to levothyroxine and takes it every morning, 30 minutes before eating. She is not taking it with any other medications. What is the most appropriate dose adjustment at this time?

1. Decrease levothyroxine dose to 2 mcg orally daily.
2. Decrease levothyroxine dose to 12.5 mcg orally daily.
3. Increase levothyroxine dose to 50 mcg orally daily.
4. Increase levothyroxine dose to 100 mcg orally daily.

Answer: 3.      Increase levothyroxine dose to 50 mcg orally daily

Rationale: Answer 3 is correct. The patient’s thyrotropin concentration is still supratherapeutic, necessitating a dosage increase (Answers 1 and 2 are incorrect). Recommended increases in the levothyroxine dose are 12.5–25 mcg/day, making Answer 4 incorrect. In addition, given the weight-based needs estimate of 1.6 mcg/kg of levothyroxine daily, this patient will likely need about 73 mcg/day of levothyroxine. Given her age and history of cardiovascular disease, it is reasonable to take a conservative approach and increase the levothyroxine dose slowly to 50 mcg daily.

Citation: Garber J, Cobin R, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract 2012;18:988-1028.

Question 5

The patient’s 25-year-old granddaughter has had three miscarriages. What testing should be done for the patient’s granddaughter, in relation to thyroid disorders?

1. Free T₄.
2. Total T₄.
3. Thyrotropin.
4. Antithyroid peroxidase antibody (TPOAb).

Answer: 4.      TPOAb

Rationale: Patients with TPOAb (Answer 4 is correct) have a higher miscarriage rate than those without these antibodies. These patients may be euthyroid, making Answers 1, 2, and 3 incorrect. Pregnant women with a positive TPOAb test may be treated with levothyroxine to decrease the risk of miscarriage. In addition, thyroid disorders may have a genetic component, making the granddaughter more susceptible to hypothyroidism (mother and grandmother have the disease).

Citation: Garber J, Cobin R, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract 2012;18:988-1028.