Presentation and Status in Health Basket
100 X 100 mcg
100 X 50 mcg
If the dose of thyroxine is increased too rapidly, symptoms such as diarrhoea, nervousness, rapid pulse, insomnia, tremors and sometimes anginal pain where there is latent myocardial ischaemia, may occur, and the dosage must be reduced or withheld for a day or two, then restarted at a lower level. A pre-therapy ECG is valuable, as changes induced by hypothyroidism may be confused with ECG evidence of ischaemia. Due to a lack of data it is not appropriate to crush thyroxine tablets and thyroxine tablets without a score-line must not be halved. Thyroxine tablets should preferably be taken on an empty stomach.
Missed dosage: If a scheduled daily dose is missed, the dose should be taken as soon as the patient remembers, unless it is almost time for the patient’s next dose. Two doses should not be taken together.
Adults: Initially 50 to 100 micrograms daily and adjust at 4 to 6 week intervals by 50 micrograms until attainment of clinical and biochemical euthyroidism. 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 4 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 thyroxine sodium on alternate days, with increments of 50 mcg 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.
Treatment of hypothyroidism, cretinism and juvenile myxoedema.
Hypersensitivity to any component of the preparation. Untreated adrenal insufficiency, untreated pituitary insufficiency, and thyrotoxicosis. Treatment with Eltroxin must not be initiated in acute myocardial infarction, acute myocarditis, and acute pancarditis. Combination therapy of levothyroxine and an antithyroid agent for hyperthyroidism is not indicated during pregnancy
Thyroxine has a narrow therapeutic index. Appropriate thyroxine dosage is based upon clinical assessment and laboratory monitoring of thyroid function tests. During the initial titration period, careful dosage titration and monitoring is necessary to avoid the consequences of under- or over-treatment. The symptoms of excessive thyroxine dosage are the same as many features of endogenous thyrotoxicosis. In order to ensure the continuity of different products of levothyroxine sodium in individual patients it should be emphasized that if patients are changed from one levothyroxine sodium product to another it should be done only with specific counseling and tight monitoring from their healthcare professional. 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, adrenal insufficiency. Thyroid autonomy should also be excluded or treated before starting therapy with thyroid hormones. Treatment with thyroxine in patients with panhypopituitarism or other causes predisposing to adrenal insufficiency may cause reactions, including dizziness, weakness, malaise, weight loss, hypotension and adrenal crisis. It is advisable to initiate corticosteroid therapy before giving thyroxine 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. 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. Thyroxine raises blood sugar levels and this may upset the stability of patients receiving antidiabetic agents. In the case of secondary hypothyroidism the cause must be determined before replacement therapy is given and if necessary replacement treatment of a compensated adrenal insufficiency must be commenced. Where thyroid autonomy is suspected a TRH test should be carried out or a suppression scintigram obtained before treatment. In postmenopausal women with hypothyroidism and an increased risk of osteoporosis supraphysiological serum levels of levothyroxine should be avoided, and, therefore, thyroid function should be checked closely. Levothyroxine should not be given in hyperthyreotic states other than as concomitant supplementation during anti-thyroid drug treatment of hyperthyroidism. Thyroid hormones are not suitable for weight reduction. Physiological doses do not result in any weight loss in euthyroid patients. Supraphysiological doses may cause severe or even life-threatening undesirable effects.
The frequency classification for these adverse reactions is not known due to a lack of robust clinical trial data to accurately determine frequency estimates.
Blood and the lymphatic system disorders: Anginal pain, cardiac arrhythmias, palpitations, tachycardia, increased blood pressure, heart failure, myocardial infarction.
Immune system disorders: Hypersensitivity reactions such as skin rash and pruritus and anaphylactic reactions. Metabolism and nutrition disorders: Increased appetite, excessive loss of weight.
Nervous system disorders: Excitability, insomnia, restlessness, headache, tremors, seizure. Rare cases of pseudotumor cerebri (benign intracranial hypertension) have been reported especially in children.
Respiratory, thoracic & mediastinal disorders: Dyspnoea.
Gastrointestinal disorders: Abdominal cramps, nausea, vomiting, diarrhoea.
Skin & subcutaneous tissue disorders: Sweating, flushing, hair loss. Musculoskeletal, connective tissue and bone disorders: Cramps in the skeletal muscle, muscular weakness, decreased bone mineral density. Excessive dose may result in craniosynostosis in infants, and premature closure of epiphyses in children with compromised adult height.
Reproductive system & breast disorders: Menstrual irregularity, impaired fertility.
General disorders & administration site conditions: Fatigue, heat intolerance, fever.
Thyroxine 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 thyroxine. Anticonvulsants such as carbamazepine and phenytoin enhance the metabolism of thyroid hormones and may displace them from plasma proteins. Initiation or discontinuation of anticonvulsant therapy may alter thyroxine dose requirements. If co-administered with cardiac glycosides, adjustment of dosage of cardiac glycoside may be necessary. The effect of sympathomimetic agents are also enhanced. Thyroxine increases receptor sensitivity to catecholamines thus accelerating the response to tricyclic antidepressants. Aluminium-containing drugs (antacids, sucralfate) have been reported in the pertinent literature as potentially decreasing the effect of levothyroxine. Drugs containing levothyroxine should therefore be administered at least 2 hours prior to the administration of aluminium-containing drugs. Same is true for iron-containing drugs and calcium carbonate. Ingestion of ion exchange resins such as, kayexalate and bile acid sequestrants such as cholestyramine and colestipol inhibits the absorption of levothyroxine sodium. Levothyroxine sodium should therefore be taken 4-5 hours before administration of such products. Sevelamer may decrease levothyroxine absorption. Therefore, it is recommended that patients are monitored for changes in thyroid function at the start or end of concomitant treatment. If necessary, the levothyroxine dose has to be adjusted. Salicylates, dicumarol, furosemide in high doses (250 mg), clofibrate and other substances can displace levothyroxine sodium from plasma proteins, resulting in an elevated fT4 fraction. Co-administration of oral contraceptives, as well as a number of other drugs, including oestrogen, tamoxifene, clofibrate, methadone, and 5-fluorouracil may increase serum concentration of thyroxine-binding globulin, and therefore increase thyroxine dosage requirements. Reports indicate that some HMG-CoA reductase inhibitors (statins), such as simvastatin and lovastatin, may increase thyroid hormone requirements in patients receiving thyroxine therapy. It is unknown if this occurs with all statins. Close monitoring of thyroid function and appropriate thyroxine dose adjustments may be necessary when thyroxine and statins are co-prescribed. A number of drugs may decrease serum concentration of thyroxine-binding globulin, and therefore decrease thyroxine dosage requirements, including androgens and anabolic steroids. Treatment with tyrosine kinase inhibitors (e.g., imatinib and sunitinib) was associated with increased thyroxine dosage requirements in hypothyroid patients. Propylthiouracil, glucocorticoids, beta-sympatholytics, amiodarone and iodine containing contrast media: These substances inhibit the peripheral conversion of T4 to T3. Due to its high iodine content amiodarone can trigger hyperthyroidism as well as hypothyroidism. Particular caution is advised in the case of nodular goitre with possibly unrecognized autonomy. Anti-diabetic agents: Levothyroxine may reduce the effect of antidiabetic agents. For this reason, blood glucose levels should be checked frequently at the start of thyroid hormone therapy and the dosage of the antidiabetic agent has to be adapted, if necessary. Protease inhibitors (e.g. ritonavir, indinavir, lopinavir) may influence the effect of levothyroxine. Close monitoring of thyroid hormone parameters is recommended. If necessary, the levothyroxine dose has to be adjusted. Sertraline, chloroquine/proguanil: These substances decrease the efficacy of levothyroxine and increase the serum TSH level. Soy-containing compounds can decrease the intestinal absorption of levothyroxine. Therefore, a dosage adjustment of Eltroxin may be necessary, in particular at the beginning or after termination of nutrition with soy supplements. A number of drugs may affect thyroid function tests and this should be borne in mind when monitoring a patient on thyroxine therapy.
Pregnancy and Lactation
Pregnancy: Thyroxine has been taken by a large number of pregnant women and women of childbearing age without any form of definite disturbances in the reproductive process having been observed so far. Thyroid, hypo- or hyperactivity in the mother may, however, unfavourably influence the foetal outcome or well-being. Combination therapy of hyperthyroidism with levothyroxine and anti-thyroid agents is not indicated in pregnancy. Such combination would require higher doses of anti-thyroid agents, which are known to pass the placenta and to induce hypothyroidism in the infant.
Lactation: Thyroxine is excreted in breast milk in low concentrations and this may be sufficient to interfere with neonatal screening for hypothroidism.
Symptoms & Signs: In addition to exaggeration of side effects the following symptoms may be seen: agitation, confusion, irritability, hyperactivity, headache, sweating, mydriasis, tachycardia, arrhythmias, tachypnoea, pyrexia, increased bowel movements and convulsions. The appearance of clinical hyper- thyroidism may be delayed for up to five days. Treatment The goal of therapy is restoration of clinical and biochemical euthyroid state by omitting or reducing the thyroxine dosage, and other measures as needed depending on clinical status.
Treatment: is symptomatic, and tachycardia has been controlled in adults by 40mg doses of propranolol given every six hours and other symptoms by diazepam and/or chlorpromazine as appropriate. Further management should be as clinically indicated or as recommended by the national poison centre, where available.