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Indications/Uses
Control of hypothyroidism, congenital hypothyroidism in infants, acquired hypothyroidism in children and juvenile myxoedema.
Dosage/Direction for Use
In younger patients, and in the absence of heart disease, a serum Levothyroxine (T4) level of 70 to 160 nanomoles per liter, or a serum thyrotrophin level of less than 5 milli-units per litre should be targeted. A pre-therapy ECG is valuable because ECG changes due to hypothyroidism may be confused with ECG evidence of cardiac ischemia. If too rapid an increase in metabolism is produced (causing diarrhoea, nervousness, rapid pulse, insomnia, tremors, and sometimes anginal pain where there is latent cardiac ischemia,) dosage must be reduced, or withheld, for a day or two, and then re-started at a lower dose level.
Adults: Initially 100 micrograms daily, preferably taken before breakfast or the first meal of the day. Adjust at three-to-four-week intervals by 50 micrograms until normal metabolism is steadily maintained. The final daily dose may be up to 100 to 200 micrograms.
Elderly: As for patients aged over 50 years.
For patients over 50 years, initially, it is not advisable to exceed 50 micrograms daily. In this condition, the daily dose may be increased by 50 micrograms at intervals of every 3-4 weeks, until stable thyroxine levels are attained. The final daily dose may be up to 50 to 200 micrograms.
Patients over 50 years with cardiac disease: Where there is cardiac disease, 25 micrograms daily or 50 micrograms on alternate days is more suitable. In these conditions, the daily dose may be increased by 25 micrograms at intervals of every 4 weeks, until stable thyroxine levels are attained. The final daily dose may be up to 50 to 200 micrograms.
For patients aged over 50 years, with or without cardiac disease, clinical response is probably a more acceptable criteria of dosage rather that serum levels.
Paediatric population: The maintenance dose is generally 100 to 150 micrograms per m2 body surface area. The dose for children depends on their age, weight and the condition being treated. Regular monitoring using serum TSH levels, as in adults, is required to make sure he/she gets the right dose. Infants should be given the total daily dose at least half an hour before the first meal of the day.
Congenital hypothyroidism in infants: For neonates and infants with congenital hypothyroidism, where rapid replacement is important, the initial recommended dosage is 10 to 15 micrograms per kg BW per day for the first 3 months. Thereafter, the dose should be adjusted individually according to the clinical findings and thyroid hormone and TSH values.
Acquired hypothyroidism in children: For children with acquired hypothyroidism, the initial recommended dosage is 12.5-50 micrograms per day. The dose should be increased gradually every 2 to 4 weeks according to the clinical findings and thyroid hormone and TSH values until the full replacement dose is reached.
Juvenile myxoedema in children: The initial recommended dosage is 25 micrograms daily. In such conditions, the daily dose may be increased by 25 micrograms at intervals of every 2 - 4 weeks, until mild symptoms of hyperthyroidism are seen. The dose will then be reduced slightly.
In children under 5 years of age, the administration of whole tablets is not recommended. It is also not recommended that tablets are crushed and dispersed in water or other liquids, owing to limited solubility which could lead to dosing inaccuracy. In this age group it is preferable to administer an approved oral solution of levothyroxine.
When applicable: Tablets are to be disintegrated in some water (10 to 15 ml) and the resultant suspension, which must be prepared freshly as required, is to be administered with some more liquid (5 to 10 ml).
Method of administration: Oral Administration.
Adults: Initially 100 micrograms daily, preferably taken before breakfast or the first meal of the day. Adjust at three-to-four-week intervals by 50 micrograms until normal metabolism is steadily maintained. The final daily dose may be up to 100 to 200 micrograms.
Elderly: As for patients aged over 50 years.
For patients over 50 years, initially, it is not advisable to exceed 50 micrograms daily. In this condition, the daily dose may be increased by 50 micrograms at intervals of every 3-4 weeks, until stable thyroxine levels are attained. The final daily dose may be up to 50 to 200 micrograms.
Patients over 50 years with cardiac disease: Where there is cardiac disease, 25 micrograms daily or 50 micrograms on alternate days is more suitable. In these conditions, the daily dose may be increased by 25 micrograms at intervals of every 4 weeks, until stable thyroxine levels are attained. The final daily dose may be up to 50 to 200 micrograms.
For patients aged over 50 years, with or without cardiac disease, clinical response is probably a more acceptable criteria of dosage rather that serum levels.
Paediatric population: The maintenance dose is generally 100 to 150 micrograms per m2 body surface area. The dose for children depends on their age, weight and the condition being treated. Regular monitoring using serum TSH levels, as in adults, is required to make sure he/she gets the right dose. Infants should be given the total daily dose at least half an hour before the first meal of the day.
Congenital hypothyroidism in infants: For neonates and infants with congenital hypothyroidism, where rapid replacement is important, the initial recommended dosage is 10 to 15 micrograms per kg BW per day for the first 3 months. Thereafter, the dose should be adjusted individually according to the clinical findings and thyroid hormone and TSH values.
Acquired hypothyroidism in children: For children with acquired hypothyroidism, the initial recommended dosage is 12.5-50 micrograms per day. The dose should be increased gradually every 2 to 4 weeks according to the clinical findings and thyroid hormone and TSH values until the full replacement dose is reached.
Juvenile myxoedema in children: The initial recommended dosage is 25 micrograms daily. In such conditions, the daily dose may be increased by 25 micrograms at intervals of every 2 - 4 weeks, until mild symptoms of hyperthyroidism are seen. The dose will then be reduced slightly.
In children under 5 years of age, the administration of whole tablets is not recommended. It is also not recommended that tablets are crushed and dispersed in water or other liquids, owing to limited solubility which could lead to dosing inaccuracy. In this age group it is preferable to administer an approved oral solution of levothyroxine.
When applicable: Tablets are to be disintegrated in some water (10 to 15 ml) and the resultant suspension, which must be prepared freshly as required, is to be administered with some more liquid (5 to 10 ml).
Method of administration: Oral Administration.
Overdosage
Symptoms: In most cases there will be no features. Signs of an overdose may include fever, chest pain (angina), racing or irregular heartbeat, muscle cramps, headache, restlessness, flushing, sweating, diarrhoea, tremor, insomnia and hyperpyrexia. These signs can take up to 5 days to appear. Atrial fibrillation may develop. Convulsions occurred in one child. There may be increased toxicity in those with pre-existing heart disease.
Management: Give oral activated charcoal if more than 10 mg has been ingested by an adult or more than 5 mg by a child, within 1 hour. If more than 10 mg has been ingested by an adult or more than 5 mg by a child, take blood 6-12 hours after ingestion for measurement of the free thyroxine concentration. The analysis does not need to be done urgently but can wait until the first working day after the incident. Patients with normal free thyroxine concentrations do not require follow up. Those with high concentrations should have outpatient review 3-6 days after ingestion to detect delayed onset hyperthyroidism. Features of clinical hyperthyroidism should be controlled with beta-blockers, e.g., propranolol.
Management: Give oral activated charcoal if more than 10 mg has been ingested by an adult or more than 5 mg by a child, within 1 hour. If more than 10 mg has been ingested by an adult or more than 5 mg by a child, take blood 6-12 hours after ingestion for measurement of the free thyroxine concentration. The analysis does not need to be done urgently but can wait until the first working day after the incident. Patients with normal free thyroxine concentrations do not require follow up. Those with high concentrations should have outpatient review 3-6 days after ingestion to detect delayed onset hyperthyroidism. Features of clinical hyperthyroidism should be controlled with beta-blockers, e.g., propranolol.
Administration
Should be taken on an empty stomach.
Contraindications
Hypersensitivity to the active substance or any of the excipients.
Thyrotoxicosis.
Adrenal gland disorder or adrenal insufficiency.
Thyrotoxicosis.
Adrenal gland disorder or adrenal insufficiency.
Special Precautions
Levothyroxine should be introduced very gradually in patients aged over 50 years and those with long standing hypothyroidism to avoid any sudden increase in metabolic demands.
Patients with panhypopituitarism or other causes predisposing to adrenal insufficiency may react to levothyroxine treatment, and it is advisable to start corticosteroid therapy before giving levothyroxine to such patients.
Levothyroxine sodium should be used with caution in patients with cardiovascular disorders, including angina, coronary artery disease, hypertension, and in the elderly who have a greater likelihood of occult cardiac disease.
To minimise the risk of adverse effects of undetected overtreatment, such as atrial fibrillation and fractures associated with low serum levels of thyroid stimulating hormone (TSH) in older patients, it is important to monitor serum TSH and adjust the dose accordingly during long term use.
In individuals suspected to have cardiovascular disease or to be at high risk, it is important to perform an ECG prior to commencement of levothyroxine treatment in order to detect changes consistent with ischemia in which case, levothyroxine should be initiated at a low dose, followed by cautious dose escalation to avoid worsening of ischemia or precipitation of an infarct.
Special care is needed for the elderly and for patients with symptoms of myocardial insufficiency, or ECG evidence of myocardial infarction.
Thyroid replacement therapy may cause an increase in dosage requirements of insulin or other anti-diabetic therapy (such as metformin). Care is needed for patients with diabetes mellitus, and diabetes insipidus.
See note as previously mentioned regarding withdrawal of treatment.
Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Subclinical hyperthyroidism may be associated with bone loss. To minimise the risk of osteoporosis, dosage of levothyroxine sodium should be titrated to the lowest possible effective level.
Parents of children receiving thyroid agent should be advised that partial loss of hair may occur during the first few months of therapy, but this effect is usually transient and subsequent regrowth usually occurs.
Care is required when levothyroxine is administered to patients with known history of epilepsy. Seizures have been reported rarely in association with the initiation of levothyroxine sodium therapy and may be related to the effect of thyroid hormone on seizure threshold.
Patients with panhypopituitarism or other causes predisposing to adrenal insufficiency may react to levothyroxine treatment, and it is advisable to start corticosteroid therapy before giving levothyroxine to such patients.
Levothyroxine sodium should be used with caution in patients with cardiovascular disorders, including angina, coronary artery disease, hypertension, and in the elderly who have a greater likelihood of occult cardiac disease.
To minimise the risk of adverse effects of undetected overtreatment, such as atrial fibrillation and fractures associated with low serum levels of thyroid stimulating hormone (TSH) in older patients, it is important to monitor serum TSH and adjust the dose accordingly during long term use.
In individuals suspected to have cardiovascular disease or to be at high risk, it is important to perform an ECG prior to commencement of levothyroxine treatment in order to detect changes consistent with ischemia in which case, levothyroxine should be initiated at a low dose, followed by cautious dose escalation to avoid worsening of ischemia or precipitation of an infarct.
Special care is needed for the elderly and for patients with symptoms of myocardial insufficiency, or ECG evidence of myocardial infarction.
Thyroid replacement therapy may cause an increase in dosage requirements of insulin or other anti-diabetic therapy (such as metformin). Care is needed for patients with diabetes mellitus, and diabetes insipidus.
See note as previously mentioned regarding withdrawal of treatment.
Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Subclinical hyperthyroidism may be associated with bone loss. To minimise the risk of osteoporosis, dosage of levothyroxine sodium should be titrated to the lowest possible effective level.
Parents of children receiving thyroid agent should be advised that partial loss of hair may occur during the first few months of therapy, but this effect is usually transient and subsequent regrowth usually occurs.
Care is required when levothyroxine is administered to patients with known history of epilepsy. Seizures have been reported rarely in association with the initiation of levothyroxine sodium therapy and may be related to the effect of thyroid hormone on seizure threshold.
Adverse Reactions
Side-effects are usually indicative of excessive dosage and usually disappear on reduction of dosage or withdrawal of treatment for a few days.
Adverse reactions listed as follows have been observed during clinical studies and/or during marketed use and are based on clinical trial data and classified according to MedDRA System Organ Class. Frequency categories are defined according to the following convention: Not known (cannot be estimated from the available data). (See table.)
Adverse reactions listed as follows have been observed during clinical studies and/or during marketed use and are based on clinical trial data and classified according to MedDRA System Organ Class. Frequency categories are defined according to the following convention: Not known (cannot be estimated from the available data). (See table.)
Some patients may experience a severe reaction to high levels of thyroid hormone. This is called a "thyroid crisis" with any of the following symptoms: Hyperpyrexia, tachycardia, arrhythmia, hypotension, cardiac failure, jaundice, confusion, seizure and coma.
Paediatric population: Heat intolerance, transient hair loss, benign intracranial hypertension, craniostenosis in infants and premature closure of epiphysis in children.
Paediatric population: Heat intolerance, transient hair loss, benign intracranial hypertension, craniostenosis in infants and premature closure of epiphysis in children.
Drug Interactions
Interactions affecting other drugs: Levothyroxine increases the effect of anticoagulants (Warfarin), and it may be necessary to reduce the anticoagulation dosage if excessive, hypoprothrombinemia and bleeding are to be avoided.
Blood sugar levels are raised, and dosage of anti-diabetic agents may require adjustment.
Tricyclic anti-depressants (e.g., amitriptyline, imipramine, dosulepin) response may be accelerated because levothyroxine increases sensitivity to catecholamines; concomitant use may precipitate cardiac arrhythmias.
The effects of sympathomimetic agents (e.g., adrenaline or phenylephrine) are also enhanced.
Cardiac glycosides: If levothyroxine therapy is initiated in digitalised patients, the dose of digitalis may require adjustment. Hyperthyroid patients may need their digoxin dosage gradually increased as treatment proceeds because initially patients are relatively sensitive to digoxin.
NSAIDs: False low plasma concentrations have been observed with concurrent anti-inflammatory treatment such as phenylbutazone or acetylsalicylic acid and levothyroxine therapy.
Beta Blockers: levothyroxine (thyroxine) accelerates metabolism of propranolol, atenolol and sotalol.
General anaesthetics: Isolated reports of marked hypertension and tachycardia have been reported with concurrent ketamine administration.
Interactions affecting Levothyroxine: Amiodarone may inhibit the de iodination of thyroxine to triiodothyronine resulting in a decreased concentration of triiodothyronine, thereby reducing the effects of thyroid hormones.
Anti-convulsant, such as carbamazepine and phenytoin, enhance the metabolism of thyroid hormones and may displace them from plasma proteins.
Initiation or discontinuation of anti-convulsant therapy may alter levothyroxine dosage requirements.
Effects of Levothyroxine may be decreased by concomitant sertraline.
Absorption of levothyroxine (thyroxine) possibly reduced by antacids, proton pump inhibitors, calcium salts, cimetidine, oral iron, sucralfate, colestipol, polystyrene sulphonate resin and cholestyramine (administration should be separated by 4-5 hours).
Metabolism of levothyroxine (thyroxine) accelerated by rifampicin, barbiturates, and primidone. (May increase requirements for levothyroxine (thyroxine) in hypothyroidism).
Imatinib: Plasma concentration of levothyroxine (thyroxine) possibly reduced by imatinib.
Beta blockers may decrease the peripheral conversion of levothyroxine to triiodothyronine.
Lipid regulating drugs: Lovastatin has been reported to cause one case each of hypothyroidism and hyperthyroidism in two patients taking levothyroxine.
Sex Hormones: Oestrogen, oestrogen containing product (including hormone replacement therapy) and oral contraceptives may increase the requirement of thyroid therapy dosage. Conversely, androgens and corticosteroids may decrease serum concentrations of Levothyroxine binding globulins.
Anti-obesity drugs such as orlistat may decrease levothyroxine absorption which may result in hypothyroidism (monitor for changes in thyroid function).
A number of drugs may affect thyroid function tests, and this should be borne in mind when monitoring a patient on levothyroxine therapy.
Post-marketing cases have been reported indicating a potential interaction between ritonavir containing products and levothyroxine. Thyroid- stimulating hormone (TSH) should be monitored in patients treated with levothyroxine at least the first month after starting and /or ending ritonavir treatment.
Drug-Food Interactions: Consumption of certain foods may affect levothyroxine sodium absorption thereby necessitating adjustments in dosing. Soybean flour (infant formula), cotton seed meal, walnuts, calcium and calcium-fortified orange juice, and dietary fibre may decrease the absorption of levothyroxine sodium from the gastrointestinal tract.
Drug-Laboratory Interactions: A number of drugs and foods are known to alter serum levels of TSH, T4 and T3 and may thereby influence the interpretation of laboratory tests of thyroid function. Changes in Thyroxine-Binding Globulin (TBG) concentration should be taken into consideration when interpreting T4 and T3 values. Drugs such as estrogens and estrogen-containing oral contraceptives increase serum TBG concentrations. TBG concentrations may also be increased during pregnancy, in infectious hepatitis and acute intermittent porphyria. Decreases in TBG concentrations are observed in nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, and after androgen or corticosteroid therapy. Familial hyper- or hypo-thyroxine binding-globulinemias have been described. The incidence of TBG deficiency is approximately 1 in 9000. Certain drugs such as salicylates inhibit the protein-binding of T4. In such cases, the unbound (free) hormone should be measured.
Blood sugar levels are raised, and dosage of anti-diabetic agents may require adjustment.
Tricyclic anti-depressants (e.g., amitriptyline, imipramine, dosulepin) response may be accelerated because levothyroxine increases sensitivity to catecholamines; concomitant use may precipitate cardiac arrhythmias.
The effects of sympathomimetic agents (e.g., adrenaline or phenylephrine) are also enhanced.
Cardiac glycosides: If levothyroxine therapy is initiated in digitalised patients, the dose of digitalis may require adjustment. Hyperthyroid patients may need their digoxin dosage gradually increased as treatment proceeds because initially patients are relatively sensitive to digoxin.
NSAIDs: False low plasma concentrations have been observed with concurrent anti-inflammatory treatment such as phenylbutazone or acetylsalicylic acid and levothyroxine therapy.
Beta Blockers: levothyroxine (thyroxine) accelerates metabolism of propranolol, atenolol and sotalol.
General anaesthetics: Isolated reports of marked hypertension and tachycardia have been reported with concurrent ketamine administration.
Interactions affecting Levothyroxine: Amiodarone may inhibit the de iodination of thyroxine to triiodothyronine resulting in a decreased concentration of triiodothyronine, thereby reducing the effects of thyroid hormones.
Anti-convulsant, such as carbamazepine and phenytoin, enhance the metabolism of thyroid hormones and may displace them from plasma proteins.
Initiation or discontinuation of anti-convulsant therapy may alter levothyroxine dosage requirements.
Effects of Levothyroxine may be decreased by concomitant sertraline.
Absorption of levothyroxine (thyroxine) possibly reduced by antacids, proton pump inhibitors, calcium salts, cimetidine, oral iron, sucralfate, colestipol, polystyrene sulphonate resin and cholestyramine (administration should be separated by 4-5 hours).
Metabolism of levothyroxine (thyroxine) accelerated by rifampicin, barbiturates, and primidone. (May increase requirements for levothyroxine (thyroxine) in hypothyroidism).
Imatinib: Plasma concentration of levothyroxine (thyroxine) possibly reduced by imatinib.
Beta blockers may decrease the peripheral conversion of levothyroxine to triiodothyronine.
Lipid regulating drugs: Lovastatin has been reported to cause one case each of hypothyroidism and hyperthyroidism in two patients taking levothyroxine.
Sex Hormones: Oestrogen, oestrogen containing product (including hormone replacement therapy) and oral contraceptives may increase the requirement of thyroid therapy dosage. Conversely, androgens and corticosteroids may decrease serum concentrations of Levothyroxine binding globulins.
Anti-obesity drugs such as orlistat may decrease levothyroxine absorption which may result in hypothyroidism (monitor for changes in thyroid function).
A number of drugs may affect thyroid function tests, and this should be borne in mind when monitoring a patient on levothyroxine therapy.
Post-marketing cases have been reported indicating a potential interaction between ritonavir containing products and levothyroxine. Thyroid- stimulating hormone (TSH) should be monitored in patients treated with levothyroxine at least the first month after starting and /or ending ritonavir treatment.
Drug-Food Interactions: Consumption of certain foods may affect levothyroxine sodium absorption thereby necessitating adjustments in dosing. Soybean flour (infant formula), cotton seed meal, walnuts, calcium and calcium-fortified orange juice, and dietary fibre may decrease the absorption of levothyroxine sodium from the gastrointestinal tract.
Drug-Laboratory Interactions: A number of drugs and foods are known to alter serum levels of TSH, T4 and T3 and may thereby influence the interpretation of laboratory tests of thyroid function. Changes in Thyroxine-Binding Globulin (TBG) concentration should be taken into consideration when interpreting T4 and T3 values. Drugs such as estrogens and estrogen-containing oral contraceptives increase serum TBG concentrations. TBG concentrations may also be increased during pregnancy, in infectious hepatitis and acute intermittent porphyria. Decreases in TBG concentrations are observed in nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, and after androgen or corticosteroid therapy. Familial hyper- or hypo-thyroxine binding-globulinemias have been described. The incidence of TBG deficiency is approximately 1 in 9000. Certain drugs such as salicylates inhibit the protein-binding of T4. In such cases, the unbound (free) hormone should be measured.
Storage
Store at temperatures not exceeding 30°C.
Shelf-life: 36 Months from manufacturing date.
Shelf-life: 36 Months from manufacturing date.
Action
Pharmacological Classification: Thyroid Hormone Replacement.
Pharmacology: Pharmacodynamics: THYVEX-50/THYVEX-100 is a tablet containing the hydrated form of Levothyroxine sodium which is used for the treatment of hypothyroidism. The thyroid gland is dependent upon 2 active principles for its main hormone activity these are Levothyroxine (tetraiodothyronine) and Triiodothyronine. These closely related iodine containing amino acids are incorporated into the glycoprotein thyroglobulin. The chief action of these hormones is to increase the rate of cell metabolism. Levothyroxine is deiodinated in peripheral tissues to form Triiodothyronine which is thought to be the active tissue form of thyroid hormone. Triiodothyronine is certainly more rapid acting and has a shorter duration of action than Levothyroxine.
The chief action of Levothyroxine is to increase the rate of cell metabolism.
Pharmacokinetics: Levothyroxine sodium is incompletely and variably absorbed from the gastrointestinal tract. It is almost completely bound to plasma proteins and has a half-life in the circulation of about a week in healthy subjects, but longer during pregnancy in patients with myxoedema. A large portion of the Levothyroxine leaving the circulation is taken up by the liver. Part of a dose of Levothyroxine is metabolized to triiodothyronine. Levothyroxine is excreted in the urine as free drug, deiodinated metabolites and conjugates. Some Levothyroxine is excreted in the faeces. There is limited placental transfer of Levothyroxine.
Pharmacology: Pharmacodynamics: THYVEX-50/THYVEX-100 is a tablet containing the hydrated form of Levothyroxine sodium which is used for the treatment of hypothyroidism. The thyroid gland is dependent upon 2 active principles for its main hormone activity these are Levothyroxine (tetraiodothyronine) and Triiodothyronine. These closely related iodine containing amino acids are incorporated into the glycoprotein thyroglobulin. The chief action of these hormones is to increase the rate of cell metabolism. Levothyroxine is deiodinated in peripheral tissues to form Triiodothyronine which is thought to be the active tissue form of thyroid hormone. Triiodothyronine is certainly more rapid acting and has a shorter duration of action than Levothyroxine.
The chief action of Levothyroxine is to increase the rate of cell metabolism.
Pharmacokinetics: Levothyroxine sodium is incompletely and variably absorbed from the gastrointestinal tract. It is almost completely bound to plasma proteins and has a half-life in the circulation of about a week in healthy subjects, but longer during pregnancy in patients with myxoedema. A large portion of the Levothyroxine leaving the circulation is taken up by the liver. Part of a dose of Levothyroxine is metabolized to triiodothyronine. Levothyroxine is excreted in the urine as free drug, deiodinated metabolites and conjugates. Some Levothyroxine is excreted in the faeces. There is limited placental transfer of Levothyroxine.
MedsGo Class
Thyroid Hormones
Features
Dosage
100mcg
Ingredients
- Levothyroxine
Packaging
Tablet 50's
Generic Name
Levothyroxine Sodium
Registration Number
DR-XY10141
Classification
Prescription Drug (RX)
Product Questions
Questions
