Behestan Pakhsh

Brand name: L-thyrox

Active ingredient (generic name): Levothyroxin

Manufacturer: Hexal

Importer: Behestan Darou

Pharmacotherapeutic group: thyroid hormone

Pharmaceutical form: 50 & 100mcg tablets

Pharmacodynamic:  

Levothyroxine is deiodinated in peripheral tissues to form triiodothyronine which is thought to be the active tissue form of thyroid hormone. The chief action of Levothyroxine is to increase the rate of cell metabolism.

Pharmacokinetic:

Levothyroxine sodium is incompletely and variably absorbed from the gastrointestinal tract. It is almost completely bound to plasma proteins and has a half-life in the circulation of about a week in healthy subjects, but longer in patients with myxoedema.  Levothyroxine is excreted in the urine as free drug, deiodinated metabolites and conjugates. Some Levothyroxine is excreted in the faeces. There is limited placental transfer of Levothyroxine.

Therapeutic indication:

Dosage and administration:

Initially 50 to 100 micrograms daily, preferably taken before breakfast. Adjust at three to four week intervals by 50 micrograms until normal metabolism is steadily maintained: this may require doses of 100 to 200 micrograms daily.

Adverse reaction:

Side-effects are usually indicative of excessive dosage and usually disappear on reduction of dosage or withdrawal of treatment for a few days. Such effects include:

Headache, flushing, fever and sweating, hypersensitivity reactions including rash, purities and edema, weight loss ,tremor, restlessness, excitability, insomnia, anginal pain, cardiac arrhythmias, palpitations, tachycardia ,diarrhoea, vomiting

Contraindication:

Hypersensitivity to any components of Levothyroxine tablets

Pharmacokinetic interactions:

Anti-convulsants, such as carbamazepine, primidone and phenytoin, enhance the metabolism of thyroid hormones and increase requirement for thyroid hormones in hypothyroidism.

Antidiabetics: Blood sugar levels are raised and dosage of anti-diabetic agents may require adjustment.

Beta Blockers: levothyroxine (thyroxine) accelerates metabolism of propranolol.

Antidepressant: Levothyroxine increases receptor sensitivity to catecholamines thus accelerating the response to tricyclic antidepressants (e.g. amitriptyline, imipramine).

NSAIDs: False low plasma concentrations have been observed with concurrent anti-inflammatory treatment such as phenylbutazone or acetylsalicylic acid and levothyroxine therapy.

Special warnings:

Levothyroxine sodium should be used with caution in patients with cardiovascular disorders, including angina, coronary artery disease and hypertension.

Levothyroxine should be introduced very gradually in elderly patients and those with long standing hypothyroidism to avoid any sudden increase in metabolic demands.

Thyroid replacement therapy may cause an increase in dosage requirements of insulin or other anti-diabetic therapy. Care is needed for patients with diabetes mellitus and diabetes insipidus.

Pregnancy and lactation:

Pregnancy category is B.

Storage temperature:  

Room temperature (15-25 C)