1. How do medication, other physiological conditions like pregnancy, and pathological conditions like acute hepatitis and chronic liver disease affect thyroid hormone metabolism and the requirement of levothyroxine if the patient is already on thyroid supplements?

There are some proteins in blood like thyroxine-binding globulin (TBG) that transport levothyroxine (T3, T4) In blood to peripheral tissue. pregnancy, acute hepatitis, oral contraceptive pills containing estrogen, and medications like tamoxifen, and raloxifene increase TBG. When TBG rises in the blood, TBG binds to free T3 and free T4 increasing the total T3, and T4 in the blood and decreasing the concentration of free T3, and free T4. Peripheral tissue senses the low level of free T3, and free T4, thus it stimulates the pituitary gland to produce more TSH. TSH in turn stimulates the thyroid gland to produce free T3 and free T4.

2. what are conditions where TBG decreases?

a. chronic liver disease

b. drugs like androgenic hormones, anabolic steroids, glucocorticoids\

3. why do these things matter?

if the patient is already a case of hypothyroidism and taking a levothyroxine supplement, then the dose of levothyroxine needs to be increased by 25% if the patient becomes pregnant or starts taking drugs like estrogen-containing pills.

4. what are other drugs that interfere with levothyroxine metabolism?

a. bile acid-binding resins (cholestyramine)

b. iron, calcium supplement

c. enzyme inducing drugs: barbiturate

d. enzyme inhibiting drugs:  amiodarone

e. inhibit thyroid hormone secretion: lithium, lugols solution, potassium iodide

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