Oroxine

Thyroxine

NAME OF THE MEDICAL PRODUCT

OROXINE^TM Tablets

QUALITATIVE AND QUANTITATIVE COMPOSITION

Tablets containing anhydrous thyroxine sodium, which is the monosodium salt of the levorotary isomer of thyroxine. 50 or 100 microgram non-scored tablets

PHARMACEUTICAL FORM

OROXINE Tablets 50mcg : White to off-white, round, bi-convex tablets imprinted GS 11 E on one face and 50 on the other. OROXINE Tablets 100mcg : White to off-white, round, bi-convex tablets imprinted GS 21 C on one face and 100 on the other.

CLINICAL PARTICULARS

Indications

Hypothyroidism.

Dosage and Administration

A pre-therapy ECG is valuable, as changes induced by hypothyroidism may be confused with ECG evidence of ischaemia. If the increase in metabolism is too rapid (causing diarrhoea, nervousness, rapid pulse, insomnia, tremors and sometimes anginal pain where there is latent myocardial ischaemia), dosage must be reduced or withheld for a day or two, then restarted at a lower level.

In younger patients, and in the absence of heart disease, a serum thyroxine (T₄) level of about 70 to 160 nanomols per litre, or a serum thyrotrophin level of less than 5 milli-units per litre, should be aimed at. In those aged over 50, and/or in the presence of heart disease, clinical response is probably a more acceptable criterion of dosage than serum levels.

Due to a lack of data to support the use of crushing tablets, it is recommended that OROXINE tablets are only prescribed to patients who are able to swallow tablets.

• Adults

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

With patients aged over 50 years, it is not advisable to exceed 50 micrograms a day initially. Where there is cardiac disease 50 micrograms on alternate days is more suitable. In this condition the daily dosage may be increased by 50 micrograms on alternate days, at intervals of approximately four weeks.

• Children

In congenital hypothyroidism and juvenile myxoedema, the largest dose consistent with freedom from toxic effects should be given. The dosage is guided by clinical response, growth assessment and appropriate thyroid function tests - clinically normal pulse rate and absence of diarrhoea or constipation are the most useful indicators. Thyrotrophin levels may remain elevated during the first year of life in children with neonatal hypothyroidism due to resetting of the hypothalamic-pituitary axis.

For infants with congenital hypothyroidism a suitable starting dose is 50 micrograms OROXINE on alternate days, with increments of 50 micrograms on alternate days at intervals of every two to four weeks until optimal response is achieved. The same dosing regimen applies to juvenile myxoedema, except that the starting dose for children older than one year may be 2.5 to 5 micrograms/kg/day. The calculated daily dose equivalent should be rounded to the nearest 25 micrograms to determine the actual prescribed dose. Contraindications Hypersensitivity to any component of the preparation. Thyrotoxicosis.

Warnings and Precautions

Patients with panhypopituitarism or other causes predisposing to adrenal insufficiency may react unfavourably to OROXINE treatment, and it is advisable to initiate corticosteroid therapy before giving OROXINE in these cases.

Special care is needed in the elderly and in patients with symptoms of myocardial insufficiency or ECG evidence of myocardial infarction or ischaemia and also those with diabetes mellitus or insipidus.

OROXINE raises blood sugar levels and this may upset the stability of patients receiving antidiabetic agents.

Interactions

OROXINE increases the effect of anticoagulants and it may be necessary to reduce the dose of anticoagulant if excessive hypoprothrombinaemia and bleeding are to be avoided.

Phenytoin levels may be increased by OROXINE.

Anticonvulsants such as carbamezapine and phenytoin enhance the metabolism of thyroid hormones and may displace them from plasma proteins. Initiation or discontinuation of anticonvulsant therapy may alter OROXINE dose requirements. If co-administered with cardiac glycosides, adjustment of dosage of cardiac glycoside may be necessary.

The effects of sympathomimetic agents are also enhanced.

OROXINE increases receptor sensitivity to catecholamines thus accelerating the response to tricyclic antidepressants.

Cholestyramine given concurrently reduces the gastrointestinal absorption of thyroxine.

Co-administration of oral contraceptives may result in an increased dosage requirement of thyroid therapy.

A number of drugs may affect thyroid function tests and this should be borne in mind when monitoring a patient on OROXINE therapy.

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