Hypothyroidism should be treated with daily administration of which of the following thyroid hormone preparations?
**Core Concept**
Thyroid hormone replacement therapy is a cornerstone in the management of hypothyroidism. The goal is to replace the deficient hormone and maintain euthyroidism. The choice of thyroid hormone preparation depends on the type of thyroid hormone deficiency, the patient's age, and the desired duration of action.
**Why the Correct Answer is Right**
Levothyroxine (T4) is the preferred initial treatment for hypothyroidism. It is administered once daily, typically in the morning, to mimic the natural circadian rhythm of thyroid hormone secretion. This allows for a consistent and stable level of T4 in the bloodstream, which is then converted to triiodothyronine (T3) by peripheral tissues. The use of T4 as the primary hormone replacement is based on its longer half-life and the ability of the body to convert it to T3 as needed.
**Why Each Wrong Option is Incorrect**
**Option A:** Thyroid extract contains both T4 and T3, but its use is not recommended due to variable and unpredictable T3 content, which can lead to fluctuations in thyroid hormone levels.
**Option B:** Triiodothyronine (T3) has a shorter half-life and is typically used in specific situations, such as in patients with severe hypothyroidism or those who cannot convert T4 to T3 adequately.
**Option C:** Desiccated thyroid (Armour thyroid) is a dried and powdered form of thyroid gland that contains both T4 and T3. However, its use is not recommended due to the same concerns as thyroid extract.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the dose of levothyroxine may need to be adjusted in patients with certain medical conditions, such as kidney or liver disease, or in those taking medications that affect thyroid hormone metabolism.
**Correct Answer: C. Levothyroxine (T4)**