Euthyrox® N 50: composition and pharmaceutical form
One Euthyrox® N 50 tablet contains 50 micrograms of levothyroxine sodium. The whole range of the medicine includes tablets of 25, 50, 75, 88, 100, 112, 125, 137, 150, 175 and 200 micrograms.
Such a wide choice of strengths exists for one reason: to fit each patient an individual daily dose so that it can be contained in one tablet a day. The 50-microgram strength suits both the start of replacement therapy in adults and a step in the gradual building-up of the dose. The tablets contain lactose — this matters for people with the rare hereditary galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption syndrome.
How Euthyrox® N 50 works
The levothyroxine in the medicine is synthetic, but in its action it fully repeats the natural main hormone of the thyroid gland. In the peripheral organs it is converted into triiodothyronine (T3) and, like the body's own hormone, acts specifically on the T3 receptors.
The body is not able to distinguish exogenous levothyroxine from endogenous. Hence the main principle of treatment: the aim is not to "stimulate" the gland but to reproduce the physiological level of the hormone, and that is why the dose is calibrated against the test results rather than against how the patient feels.
Indications
The medicine at a strength of 50 micrograms is used to treat non-toxic goitre, to prevent its recurrence after surgical removal — taking into account what part of the thyroid function has been retained after the operation — as replacement therapy in hypothyroidism and as suppressive therapy in thyroid cancer.
The low strengths, including 50 micrograms, are also used together with antithyroid agents in the treatment of thyrotoxicosis: once the euthyroid state has been reached, adding levothyroxine makes it possible to continue the antithyroid therapy. In addition, individual strengths are used in diagnostic tests of thyroid suppression.
Method of use and dosage
The daily dose is taken whole at one time: in the morning, on an empty stomach, half an hour before breakfast, with a small amount of liquid — half a glass of water is enough. Infants are given the whole daily dose once, at least 30 minutes before the first feed: the tablet is dissolved in a small amount of water immediately before it is given and the resulting suspension is administered, followed by a little more liquid.
The dose is determined by the laboratory values and the clinical picture, not by a standard scheme. The baseline serum level of thyroid-stimulating hormone serves as the reference point: in many patients the T4 and free T4 concentrations are raised, so it is harder to judge by them. One starts with low doses and raises them every 2–4 weeks up to the full replacement dose. The usual daily doses of levothyroxine sodium are these: in non-toxic goitre and to prevent its recurrence after surgery, 75–200 micrograms; in hypothyroidism in adults, a starting dose of 25–50 micrograms and a maintenance dose of 100–200 micrograms; in thyroid cancer, for suppressive therapy, 150–300 micrograms; together with antithyroid agents in thyrotoxicosis, 50–100 micrograms.
Who needs to start especially slowly
In elderly patients, in people with ischaemic heart disease and in those whose hypothyroidism is severe or long-standing, treatment is started with a very low dose — for example 12.5 micrograms a day — and it is raised in steps of 12.5 micrograms as well, but at wide intervals, say once every two weeks, with frequent monitoring of the hormones. In such cases one sometimes has to stop at a dose below the optimum, at which the TSH does not fully return to normal. Patients with a low body weight and a large nodular goitre, as practice shows, need smaller doses. In newborns and infants with congenital hypothyroidism, by contrast, the deficiency has to be made good quickly: for the first 3 months 10–15 micrograms per kilogram of body weight a day are given, and thereafter the dose is adjusted individually according to the clinical picture, the hormone level and the TSH.
Contraindications
Euthyrox® N 50 is not used in the following cases:
- hypersensitivity to levothyroxine or to any excipient of the medicine;
- untreated insufficiency of the adrenal cortex;
- untreated pituitary insufficiency;
- untreated thyrotoxicosis;
- a recent myocardial infarction — treatment is not started in that period;
- myocarditis;
- acute inflammation of all the layers of the heart, that is, pancarditis.
Special warnings and precautions
Before starting therapy with thyroid hormones the doctor must rule out or begin treating coronary insufficiency, angina pectoris, atherosclerosis of the vessels, arterial hypertension, pituitary and adrenal cortex insufficiency, and also autonomous thyroid function; if the latter is suspected, a thyroliberin test or suppression scintigraphy is performed. If the hypothyroidism is secondary, its cause is established first and, if necessary, replacement treatment for compensated adrenal insufficiency is begun. In patients with coronary or heart failure and with tachyarrhythmias even mild drug-induced hyperthyroidism must not be allowed, so their hormone level is checked often.
- where there is a risk of psychotic disorders one starts with low doses, raises them gradually and watches the condition attentively; if psychotic symptoms appear, the dose is reviewed;
- in postmenopausal women with hypothyroidism and a high risk of osteoporosis, levothyroxine levels above the physiological range are not allowed and the thyroid function parameters are followed closely;
- in thyrotoxicosis levothyroxine is used exclusively in combination with antithyroid agents;
- switching to a medicine from another manufacturer requires adjusting the dose according to the clinical response and the test results;
- orlistat can cause hypothyroidism or worsen its control: before starting it a consultation with a doctor is needed, the medicines are taken at different times of day, the levothyroxine dose is sometimes changed and the hormones are monitored;
- patients with diabetes mellitus and those receiving anticoagulants need additional monitoring;
- because of the lactose, the medicine is not suitable in hereditary galactose intolerance, Lapp lactase deficiency and glucose-galactose malabsorption syndrome.
No studies of the influence on the ability to drive a car and to operate machinery have been carried out, but since levothyroxine is identical to the body's own thyroid hormone, no such influence is expected when it is taken in the prescribed doses.
Drug interactions
Part of the interactions has to do with the absorption of the medicine. Colestyramine and colestipol inhibit it: levothyroxine is taken 4–5 hours before them. Agents containing aluminium — antacids and sucralfate — and also iron preparations and calcium carbonate are taken no earlier than 2 hours after levothyroxine. Products containing soya reduce the absorption of the hormone in the intestine, so when they are started or stopped the dose sometimes has to be changed. Sevelamer also lowers absorption and requires monitoring of thyroid function at the beginning and at the end of the combined use.
Another group of interactions concerns the metabolism and binding of the hormone. Salicylates, dicoumarol, furosemide at a dose of 250 mg and clofibrate displace levothyroxine from its binding to plasma proteins, raising the free T4 level; phenytoin does the same and also speeds up its hepatic metabolism. Barbiturates and carbamazepine, as enzyme inducers, increase the hepatic clearance of the hormone, while tyrosine kinase inhibitors (imatinib, sunitinib), sertraline and the combination of chloroquine with proguanil reduce the efficacy of levothyroxine and raise the TSH. Protease inhibitors — ritonavir, indinavir, lopinavir — call for strict monitoring of the thyroid parameters. Propylthiouracil, glucocorticoids, beta blockers, amiodarone and iodine-containing radiographic contrast media inhibit the conversion of T4 into T3 in the periphery; amiodarone, because of its high iodine content, is capable of causing both hyperthyroidism and hypothyroidism, which matters especially in nodular goitre with possible unrecognised autonomy. Levothyroxine itself weakens the action of glucose-lowering medicines and enhances that of anticoagulants by displacing them from protein binding, so at the start of treatment both the glucose and the clotting parameters are monitored. In women taking oestrogen-containing contraceptives or hormone replacement therapy the need for levothyroxine may increase.
Pregnancy and breastfeeding
Replacement therapy is not interrupted either in pregnancy or during breastfeeding — on the contrary, during pregnancy the need for the medicine may grow. There are no data on a teratogenic effect or a toxic influence on the foetus with the recommended doses. At the same time, excessively high doses during pregnancy can affect the development of the foetus and of the child after birth negatively, so monitoring the test results in this period is especially important.
Levothyroxine passes into breast milk, but at therapeutic doses its amount is too small to cause hyperthyroidism in the child or to suppress TSH secretion. The combination of levothyroxine with antithyroid agents is not used in pregnancy: it would require large doses of the antithyroid medicine, and that crosses the placenta in active amounts and can cause hypothyroidism in the foetus — which is why thyrotoxicosis in pregnant women is treated with antithyroid agents alone. Diagnostic tests with suppression of thyroid function are not carried out in pregnancy, since the administration of radioactive substances is contraindicated.
Adverse effects
If the medicine is used as prescribed and the clinical and laboratory parameters are monitored, there should be no undesirable reactions. They arise when the individual tolerance threshold is exceeded or in an overdose — especially if the dose was built up too quickly at the start of treatment — and they represent the picture of hyperthyroidism.
- disturbances of the heart rhythm, including atrial fibrillation and extrasystoles;
- tachycardia, palpitations, anginal pain;
- headache, tremor, motor restlessness, insomnia;
- muscle weakness and muscle cramps;
- flushes, fever, increased sweating, weight loss;
- vomiting, diarrhoea, disturbances of the menstrual cycle;
- benign intracranial hypertension;
- in hypersensitivity — allergic reactions, above all of the skin and the airways; angioedema has been described.
When such symptoms appear the daily dose is reduced or the medicine is withdrawn for several days, and once the symptoms have passed treatment is cautiously resumed — now with a smaller dose or with a slower build-up.
Overdose
In an overdose hyperthyroidism develops, and in patients at risk of psychotic disorders an acute psychosis is possible. What confirms an overdose most reliably is a raised T3 concentration — this parameter is more informative than T4 or free T4. Clinically an overdose looks like a sharp acceleration of the metabolism.
Treatment is interrupted and laboratory tests are carried out; the extent of the help depends on the degree of the overdose. The manifestations of the β-sympathomimetic action — tachycardia, restlessness, agitation, hyperkinesia — are relieved with beta blockers, and in a massive overdose plasmapheresis may be needed. In sensitive patients, when the individual tolerance threshold is exceeded, isolated cases of seizures have been described; with many years of levothyroxine abuse several cases of sudden cardiac death have been recorded.
How to get a prescription for Euthyrox® N 50 online
Levothyroxine is dispensed on prescription: the dose depends on the diagnosis, the age, the state of the heart and the test results, and changing it on one's own easily leads to an overdose or to undertreated hypothyroidism.
During the online consultation the doctor will assess the TSH and hormone values, any concomitant illnesses and the medicines being taken, will explain the rules for taking it on an empty stomach and, if there are no contraindications, will issue an electronic prescription — the medicine can be collected from a pharmacy using its code.
