Thyroid Hormones include- natural and synthetic derivatives. The natural products , desiccated thryroid and thyroglobulin are derived from beef or pork. Synthetic derivatives include Levothyroxine , Liothyroxine and Liotrix. Refer Thyroglobulin

 Thyroid hormones potentiate the hypothrombinemic effects of oral anticaogulant agents such as warfarin.

Administration of thyroxine in diabetic patients may result in an increase in patients requirement for insulin/hypoglycemic medication, as thyroxine raises blood sugar levels.

Anticonvulsants such as carbamazepine and phenytoin enhance the metabolism of thyroid hormones and displace them from plasma proteins.

Phenobarbital induces hepatic enzymes and increase the rate of degradation of thyroid hormones. Therefore thyroxin dosage may need to be increased concurrently.

Beta-adrenergic blocking agents may decrease peripheral conversion of T4 to T3 , reducing the efficacy of exogenous thyroxine.

Estrogens increase serum throxine- binding globulin levels, thereby decreasing the unbound fractions of T3 and T4.

Administration of estrogen containing preparations to hypothyroid patients may cause an increase of throxine requirements .

If administered with cardiac glycosides adjustment of dosage of cardiac glycosides may be necesary

Hypothyroidism

Thyroid Hormones include natural and synthetic derivatives. The natural products , desiccated thryroid and thyroglobulin are derived from beef or pork. Synthetic derivatives include Levothyroxine , Liothyroxine and Liotrix. Refer Thyroglobulin 

It is confined to hypersensity to or intolerance of an ingredient of the tablets and toxicity due to overdosage of thyroxine. Over dosage may increase weight loss, Increased appetite , Palpitations, nervousness,

Diarrhoea,abdominal cramps, Sweating, tachycardia, Increased pulse and blood pressures, Angina pectoris,cardiac arrhythmias, Tremors, headache, Insomnia, heat intolerance, Fever, and dysmennorrhea.

Thyrotoxicosis,acute myocardial infaction.

Special precautions: Adrenal insufficiency,lactation.

Hypothyroidism Ideally synthetic T4 replacement should be taken in the morning, 30 minutes before eating.

Dosage-

For management of mild hypothyroidism, the usual initial dose is 50ug once daily

Dosage may be increased in increments of 25 to 50ug/day at intervals of 2 to 4 weeks until desired response is obtained. For management of severe hypothyroidism- initial dose is 12.5 to 25ug once daily.

Dosage may be increased by increments of 25 to 50ug/day at intervals of 2 to 4 weeks until the desired response is obtained The usual maintenance dose for full replacement therapy is 100 to 200ug/day

1. Replacement therapy is to be taken for life, except in cases of transcient hypothyroidism, usually associated with thyroditis, and in those receiving a trial of the drug.

2. Take a single daily dose preferably before breakfast

3. Brand interchange- Do not change from one brand of this drug to another without consulting your pharmacist or physician. Products manufactured by different companies may not be equally effective.

4. Do not discontinue medication except on advice of a physician

5. Notify physician if headache, nervousness, diarrhea, excessive sweating heat intolerance, chest pain, increased pulse rate, palpitations(symptoms of hyperthyroidism) or any usual event occurs

6. Partial loss of hair may be experienced by children in the first few months of therapy, but this usually a transcient phenomenon that result in later recovery

7. Not for use as primary or adjunctive therapy in a weight control program

8. If levothyroxine is taken on an empty stomach, absorption is increased.

Pharmacology- The thyroid gland largely secretes T4 (an inactive prohormone) and to a lesser extent trilodothroxine ( T3) . T4 is converted o T3 in the periphery , which is the active thyrpoid hormone. It acts by binding to the intracellular thyroid hormone receptors and acting as transcription factors to either activate or repress genes.

Pharmacodynamicsa- Thyroxine treatment when taken orally., provides hormones that is absorbed from the gastrointestinal tract.Thyroxine sodium is identical to that produced naturally in human thyroid gland and cannot be distinguished from thyroine that is secreted endogenously.

Following oral admin. thyroxine sodium ,absorption varies if taken with food. It gets bound to serum proteins and has an elimination half life of 6 to 7 days in the euthyroid subject. In hyperthyroidism, half-life is shortened and in hypothroidism and pregnancy

Therefore thyroxine administration results in serum concentrations of both T4 and T3 since the only source of the latter hormone is the seady peripheral deiodination of T4. Deiodination occurs in various tissues, mainly in liver and kidney. T3 is found to be approximately 4 times more poitent than T4.

Not to taken with food

Observe caution