USMLE Internal Medicine Review 11 02 Treatment of Hypothyroidism

USMLE Internal Medicine Review 11 02 Treatment of Hypothyroidism

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Let’s start our USMLE Review with Hypothyroidism and Hyperthyroidism from the Gold Standard USMLE Foundations of Medicine Audio Review program.

 

Play USMLE Audio MP3 11 02 Treatment of Hypothyroidism Below

 

Begin 11 02 Treatment of Hypothyroidism Transcription

Moving on to treatment, hypothyroidism is treated with Levothyroxine or T4, which is available in purer form and is stable and inexpensive.

How does Levothyroxine also harness the benefits of T3?

  • Triiodothyronine. T4 is converted intracellularly into T3. So both hormones become available though only one is administered.

Why is the desiccated form of thyroid medication unsatisfactory?

  • Desiccated thyroid is unsatisfactory because of its variable hormone content.

And why is T3 in the form of Liothyronine also unsatisfactory?

  • Liothyronine is unsatisfactory because of its rapid absorption, short half-life, and transient effects.

What about T4 Levothyroxine, is it better absorbed than Liothyronine?

  • Levothyroxine is well absorbed and blood levels are easily monitored by following FT4 or FT4i and serum TSH levels.

What is the half-life of Levothyroxine?

  • The half-life of Levothyroxine is seven days. It needs to be given only once daily.

Beginning about two hours after administration of oral Levothyroxine 0.1 to 0.5mg we can expect a rise in free Thyroxine or free Thyroxine index of about how many micrograms?

  • A rise of 1-2µg/dL.

And we can also expect a concurrent fall in TSH of about how many micro units?

  • About 1-2 µunits/mL.

About how long can we expect these changes in FT4 or FT4i and TSH to last?

  • About 8-10 hours.

Please pause the tape and give two reasons why it is best to take the daily Levothyroxine dose in the morning.

  • First, to avoid insomnia as a side effect. And second, to obtain fasting blood draws for consistent monitoring of serum Thyroxine levels.

Student doctor please pause the tape and summarize use of Levothyroxine in the treatment of hypothyroidism. Please include T3 conversion, unsatisfactory forms of thyroid medication, half-life, dose and effects, and time of administration.

  • Hypothyroidism is treated with T4 (Levothyroxine). It is available in pure form and is stable and inexpensive. Levothyroxine is converted intracellularly to T3, so benefits of both T3 and T4 are harnessed. Unsatisfactory forms of thyroid medication include desiccated thyroid due to its variable hormone content and T3 as Liothyronine because of its rapid absorption, short half-life and transient effects. The half-life of Levothyroxine is 7 days, so it need be taken only once daily.  It is well absorbed and easily followed by monitoring free Thyroxine or free Thyroxine index and TSH levels. There is a rise in FT4 or FT4i of about 1-2µg/dL with concurrent fall in TSH of about 1-2 µunits/mL, starting around 2 hours and lasting 8-10 hours after an oral dose of Levothyroxine 0.1 to 0.5mg is administered. It is best to take Levothyroxine in the morning to avoid insomnia as a side effect and also for fasting blood draws for consistency of monitoring of serum Thyroxine levels.
  • It should be noted that young children need a surprisingly high dose of Levothyroxine compared to adults. For example, the average dose for a 1-5 year old child is 5-6 µg/kg/day, while the average dose for adults is only 1-2 µg/kg/day. And concurrent administration of aluminum preparations or cholestyramine may modify T4 absorption and call for higher Levotyroxine doses.

Ok, we’ll look at the toxic effects of Levotyroxine before discussing specific treatment of myxedema coma and myxedema with heart disease.

Are there reported instances of allergy to pure Levothyroxine?

  • Not to pure Levothyroxine itself but it’s possible a patient may be allergic to coloring dye or some component of the tablet.

Major toxic reactions to Levothyroxine overdose are hyperthyroid symptoms, especially cardiac symptoms, along with which condition of bone reduction?

  • Osteoporosis.

And the most common thyrotoxic cardiac symptom is arrhythmia, especially which two varieties?

  • The two most common toxic arrhythmic reactions to Levothyroxine overdose are paroxysmal atrial tachycardia or fibrillation.

What are four other symptoms of overdose which may be troublesome?

  • Go ahead and try to list these in any order. Other symptoms of Levothyroxine overdose include excessive warmth, insomnia, restlessness and tremor.

How can the symptoms of Levothyroxine overdose be corrected?

  • Simply by omitting the daily dose of Levothyroxine for three days and then reducing the dosage to correct any problem symptoms.

Student doctor please pause the tape and summarize for toxic effects for Levothyroxine, include allergy and overdose symptoms.

  • There are no reported instances of allergy to pure Levothyroxine itself though a few patients may develop an allergy to the coloring dye or other component of the tablet. Major toxic reactions to Levothyroxine overdose are hyperthyroidism symptoms, especially cardiac ones, and osteoporosis. The chief cardiac symptom is arrhythmia, particularly paroxysmal atrial tachycardia or fibrillation. Other symptoms of T4 overdose include excessive warmth, insomnia, restlessness and tremor. Omitting three days of Levothyroxine doses and then reducing the dosage should correct for any overdose symptoms.

****END OF TRANSCRIPTION****

 

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