T3 25MCG

Description

PHARMACOLOGICAL CLASSIFICATION

Pharmacodynamic properties: Liothyronine sodium is a naturally occurring thyroid hormone. The biological action of Liothyronine sodium is quantitatively similar to that of Levothyroxine sodium, but the effects develop in a few hours and disappear within 24 to 48 hours of stopping treatment.

PHARMACOKINETICS

Absorption: Liothyronine sodium is almost completely absorbed from the gastro-intestinal tract.

Distribution: It is less readily bound to plasma proteins than thyroxine. About 0.5% is in the unbound form.

Elimination: The half-life of liothyronine in euthroidism is 1 to 2 days. Thyroid hormones do not readily cross the placenta. Minimal amounts are excreted in breast milk.

INDICATION

Liothyronine is indicated in adults and children for the treatment of coma of myxoedema, the management of severe chronic thyroid deficiency and hypothyroid states occurring in the treatment of thyrotoxicosis. Liothyronine sodium can be used also as an adjunct to carbimazole to prevent sub-clinical hypothyroidism developing during carbimazole treatment of thyrotoxicosis. Liothyronine sodium may be preferred for treating severe and acute hypothyroid states because of its rapid and more potent effect, but thyroxine sodium is normally the drug of choice for routine replacement therapy.

CONTRAINDICATION

Hypersensitivity to the active substance or to any of the excipients of this product. Patients with angina of effort or cardiovascular diseases and thyrotoxicosis.

SPECIALWARNINGS AND PRECAUTION

In severe and prolonged hypothyroidism, adrenocortical activity may be decreased. When thyroid replacement therapy is started, metabolism increases more than adrenocortical activity and this can lead to adrenocortical insufficiency requiring supplemental adrenocortical steroids. Liothyronine rather than levothyroxine would be the replacement therapy of choice during block and replace treatment of thyrotoxicosis with propylthiouracil (PTU) due to the inhibition by PTU of the peripheral conversion of T4 to T3. Liothyronine sodium treatment may result in an increase in insulin or anti-diabetic drug requirements. Care is required for patients with diabetes mellitus and diabetes insipidus. In myxoedema, care must be taken to avoid imposing excessive burden on cardiac muscle affected by prolonged severe thyroid depletion. Particular care is needed in the elderly who have a greater risk of occult cardiovascular disease. Baseline ECG is recommended prior to commencement of liothyronine treatment in order to detect changes consistent with ischaemia. Patients should undergo cardiovascular monitoring, including periodic ECGs, during liothyronine treatment. Liothyronine is contraindicated in established myocardial ischaemia (see section 4.3) in which case, levothyroxine, with cautious dose escalation, is recommended instead. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medication. Panhypopituitarism or predisposition to adrenal insufficiency (initiate corticosteroid therapy before starting liothyronine), pregnancy, breast-feeding (see section 4.6 Pregnancy and lactation). If metabolism increases too rapidly (causing diarrhoea, nervousness, rapid pulse, insomnia, tremors and sometimes anginal pain where there is latent myocardial ischaemia), reduce dose or withhold for 1-2days and start again at a lower dose. Thyroid function should continue to be monitored throughout treatment to avoid over- or under-treatment. The risks of over-treatment include atrial fibrillation, osteoporosis and bone fractures.

INTERACTION WITH OTHER MEDICINALPRODUCTS AND OTHER FORMS OFINTERACTION

Liothyronine sodium therapy may potentiate the action of anticoagulants. Phenytoin levels may be increased by liothyronine. Anticonvulsants, such as carbamazepine and phenytoin enhance the metabolism of thyroid hormones and may displace thyroid hormones from plasma proteins. Initiation or discontinuation of anticonvulsant therapy may alter liothyronine dose requirements. If co-administered with cardiac glycosides, adjustment of dosage of cardiac glycoside may be necessary. Cholestyramine and colestipol given concurrently reduces gastrointestinal absorption of liothyronine. Liothyronine raises blood sugar levels and this may upset the stability of patients receiving antidiabetic agents. Liothyronine increases receptor sensitivity to catecholamines thus accelerating the response to tricyclic antidepressants. A number of drugs may affect thyroid function tests and this should be borne in mind when monitoring patients on liothyronine therapy. Co-administration of oral contraceptives may result in an increased dosage requirement of liothyronine sodium. Amiodarone may inhibit the deiodination of thyroxine to triiodothyronine resulting in a decreased concentration of triiodothyronine with a rise in the concentration of inactive reverse triiodothyronine. As with other thyroid hormones, Liothyronine may enhance effects of amitriptyline and effects of imipramine. Metabolism of thyroid hormones accelerated by barbiturates and primidone (may increase requirements for thyroid hormones in hypothyroidism). Requirements for thyroid hormones in hypothyroidism may be increased by oestrogens.

FERTILITY, PREGNANCYAND LACTATION

Pregnancy Safety during pregnancy is not known. The risk of foetal congenital abnormalities should be weighed against the risk to the foetus of untreated maternal hypothyroidism. Breast-feeding Liothyronine sodium is excreted into breast milk in low concentrations. This may interfere with neonatal screening programmes. Fertility No human or animal data on the effect of active substance liothyronine on fertility are available.

EFFECTS ON ABILITYTO DRIVE AND USE MACHINES

Liothyronine Sodium tablets have no or negligible influence on the ability to drive and use machines.

DOSAGE AND DIRECTION FOR USE

Posology Adults: Starting dose of 10 or 20 micrograms every 8 hours, increasing after one week, if necessary, to the usual recommended daily dose of 60 micrograms in two or three divided doses.

Myxoedema Coma: 60 micrograms given by stomach tube, then 20 micrograms every 8 hours. It is more usual to start treatment with intravenous liothyronine.

Adjunct to carbimazole treatment of thyrotoxicosis: 20 micrograms every 8 hours.

Paediatric population: Children below 12 years: Adose of 5 micrograms daily. Adolescents: 12 – 17 years: Initially 10-20 micrograms daily; increased to 60 micrograms daily in 2-3 divided doses. Elderly: Adose of 5 micrograms daily.

Method of administration For oral use only. Patients who have difficulty in swallowing a whole tablet, such as the elderly and young children, a whole tablet may be crushed and allowed to dissolve, with swirling, in a minimum 20 ml of water for 5 minutes. The entire volume of liquid should be consumed to ensure ingestion of the full dose. Solubility of liothyronine in water enables this as a method of administration.

OVERDOSE

If patient is seen within a few hours of overdosage: gastric lavage or emesis. There may be exaggeration of the side effects as well as agitation, confusion, irritability, hyperactivity, headache, sweating, mydriasis, tachycardia, arrhythmias, tachypnoea, pyrexia, increased bowel movements and convulsions. Treatment is symptomatic. Tachycardia in adults may be controlled with 40mg propranolol every 6 hours.