Adults
- Young, healthy adults with no cardiac/respiratory disease are started with 1.6 mcg/kg/day of thyroxine sodium administered once daily.
- In elderly patients or in younger patients with cardiovascular disease dose required is lower than the usual adult dose i.e. <1mcg/kg/day, administered once a day. To start with in elderly patients 12.5 to 50 mcg of thyroxine sodium are given daily and increment of 12.5 to 25 mcg are made at 3-6 week intervals if required.
- Women who are maintained on thyroxine sodium during pregnancy may require increased doses.
- Treatment of subclinical hypothyroidism, when indicated may require lower than usual replacement doses; (1mcg/kg/day). Patients for whom treatment is not initiated should be monitored yearly for changes in clinical status, TSH and thyroid antibodies.
- In patients with associated adrenal insufficiency, low doses of thyroxine sodium are started only after initial treatment with glucocorticoids.
Dose Titration
The initial dose of thyroxine sodium administered depends on patient’s age, on the severity and duration of the hypothyroidism and on the existence of the underlying cardiovascular disease.
The dosage needs to be titrated against TSH levels according to individual patient’s needs. The patient should be re-evaluated and the serum TSH level should be measured in about 6- 8 weeks. The dose of thyroxine should be increased if the serum TSH concentration is elevated and decreased if it is low. Individualization and titration of proper dose is critical, aiming at normalisation of serum TSH levels.
- If proper dosage adjustment is not done then under-treatment can lead to persistence and exacerbation of symptoms can lead to end organ damage, while over-treatment can lead to following side effects.
Side effects of over-treatment with thyroxine sodium
a) Children
- thyrotoxicosis due to thyroid hormone
- increased intracranial pressure
- craniosynastosis
b) Adults
- accelerates bone loss in postmenopausal women
- increased heart rate
- increased left ventricular wall thickness and contractibility
Drug Interactions
Factors influencing the requirements of thyroxine sodium treatment
I Increased requirement
II a) Drugs leading to decreased absorption of thyroxine
- Sucralfate
- Aluminium hydroxide
- Ferrous sulphate
b) Drugs leading to increased clearance of thyroxine
- Rifampicin
- Carbamazepine
- Phenytoin
c) Drugs that prevent conversion of T4 to T3
- Glucocorticoids
- Amiodarone
Monitoring and Follow up
Depending on the above factors dose of thyroxine sodium may need adjustment.
Hypothyroidism needs life long treatment & patient compliance can be an issue hence monitoring & follow up are important
Adults :
- Titration of dosage of thyroxine is done to maintain TSH in normal range of 0.2-5mIU/L and in cases of central hypothyroidism to maintain T4 levels in normal range (5- 13.5 mg/dl)
- Follow up of these patients is done with TSH testing at 6-8 weeks intervals
- In severe hypothyroid patients, older patients or in young patients with a history of a cardiovascular disease TSH testing is done at 3-6 weeks interval
- In central hypothyroidism FT4 /T4 testing at 4-6 week intervals
- Once the dose is titrated and TSH /T4 maintained within normal limits, patient should be followed up at 6 months or yearly intervals
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