Special Warning : אזהרת שימוש

4.4    Special warnings and precautions for use
Laboratory monitoring
Eltroxin has a narrow therapeutic index. Optimal Eltroxin dosing is based on a clinical assessment and laboratory monitoring of tests of thyroid function. During the initial titration period a careful dose titration and monitoring is necessary to avoid the consequences of excessive or inadequate treatment. The symptoms of a high dosage can be compared to many of the traits observed for endogenous thyrotoxicosis.

Interference with laboratory tests:
Biotin may interfere with thyroid immunoassays based on the interaction of biotin with streptavidin, leading to either falsely low or falsely high test results. The risk of interference increases with higher doses of biotin.

When interpreting laboratory test results a possible interference with biotin should be taken into account, in particular if an inconsistent correlation with the clinical presentation is observed.

For patients taking products containing biotin, laboratory personnel should be informed when a thyroid test is requested. Alternative tests that are not sensitive to interference with biotin should be used if available (see section 4.5).

Levothyroxine should not be used for treatment of obesity or weight loss.
Thyroid hormones are not suitable for weight reduction. In euthyroid patients, treatment with levothyroxine will not result in weight loss. Higher doses can cause serious and even life-threatening side effects, especially if treated concomitantly with certain weight-reducing agents, and in particular with sympathomimetic amines.

Weight loss medicine: Orlistat may reduce the absorption of levothyroxine, which may lead to hypothyroidism. To avoid this, orlistat and levothyroxine should be administered at least 4 hours apart. Regular monitoring of changes in the thyroid function is required (see section 4.5).

If switching to another medicinal product containing levothyroxine is necessary, close monitoring, including clinical and biological monitoring during the transitional period, is necessary due to a potential risk of thyroid disorders. In some patients, a dose adjustment may be necessary.

Before starting therapy with thyroid hormones or before performing a thyroid suppression test, the following diseases or medical conditions should be excluded or treated: coronary failure, angina pectoris, arteriosclerosis, hypertension, pituitary insufficiency. Thyroid autonomy should also be excluded or treated before starting therapy with thyroid hormones.
Special patient populations
Treatment with Eltroxin in patients with pituitary insufficiency or other causes of adrenal insufficiency may cause dizziness, weakness, malaise, weight loss, hypotension and Addison's crisis. Treatment with glucocorticoids should therefore be initiated prior to starting treatment with levothyroxine. In case of adrenocortical dysfunction, this should be treated with appropriate replacement therapy prior to initiation of levothyroxine therapy to prevent acute adrenal insufficiency (see section 4.3).

Eltroxin should be used with caution to elderly and in patients where heart insufficiency, myocardial infarction or ischaemia as well as diabetes mellitus or insipidus is present. An excessive initial dose or a too rapid dose escalation may cause or aggravate symptoms such as angina pectoris, arrhythmia, myocardial infarction, heart insufficiency or a sudden increase in blood pressure. See section 4.2.
Even slight drug-induced hyperthyroidism must be avoided in patients with coronary failure, cardiac insufficiency or tachycardiac arrhythmias. Hence frequent checks of thyroid hormone parameters must be made in these cases.

In cases of secondary hypothyroidism, the cause must be found prior to giving replacement treatment, and treatment of a compensated adrenal insufficiency should be initiated if necessary.

Patients with myxoedema have increased sensitivity to thyroid hormones. In these patients, the initial dose should be low and dose escalation should take place slowly.

Absorption of levothyroxine is reduced in patients with malabsorption. It is recommended to treat the malabsorption condition to ensure an effective levothyroxine treatment.

In patients treated with levothyroxine the thyroxine level in serum may decrease and the TSH level increase during pregnancy. When pregnancy is established, the dose of levothyroxine should be increased. TSH should be measured more frequently during pregnancy and an increased level must immediately be corrected by increasing the dose of levothyroxine. Post-partum the dose of levothyroxine may be reduced to the level before pregnancy.

Haemodynamic parameters should be monitored when initiating levothyroxine treatment in premature neonates with a very low birth weight, as circulatory collapse may occur due to immature function of the adrenals.

In postmenopausal women with hypothyroidism and an increased risk of osteoporosis, supra-physiological serum levels of levothyroxine should be avoided, therefore the thyroid function should be monitored closely.

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