Levothyroxine oral
- Drugs List
- Therapeutic Indications
- Dosage
- Contraindications
- Precautions and Warnings
- Pregnancy and Lactation
- Side Effects
- Monograph
Presentation
Oral formulations of levothyroxine.
Drugs List
Therapeutic Indications
Uses
Adjunctive treatment of thyroid cancer
Juvenile myxoedema
Treatment of diffuse non-toxic goitre
Treatment of Hashimoto's thyroiditis
Treatment of hypothyroidism
Dosage
The dose should be determined on an individual basis taking into account clinical response, regular monitoring and biochemical tests.
Duration of treatment is usually for life in the case of hypothyroidism, non-toxic goitre and goitre associated with Hashimoto's thyroiditis.
Adults
Hypothyroidism
For patients aged over 50 years, with or without cardiac disease, clinical response is probably a more acceptable criteria of dosage than serum levels.
Patients over 50 years (without cardiac disease)
Initial dose: 25micrograms to 50micrograms daily before breakfast.
Adjust by 25microgram to 50microgram increments at three to four week intervals until clinical response and plasma thyroxine and thyroid stimulating hormone levels suggest the thyroid deficiency is corrected.
Maintenance dose: 50micrograms to 200micrograms daily.
Patients over 50 years (with cardiac disease)
Initial dose: 25micrograms daily before breakfast or 50micrograms on alternate days.
Adjust by 25microgram increments every four weeks until clinical response and plasma thyroxine and thyroid stimulating hormone levels suggest the thyroid deficiency is corrected.
Maintenance dose: 50micrograms to 200micrograms daily.
Patients under 50 years
Initial dose: 50micrograms to 100micrograms daily before breakfast.
Adjust by 25microgram to 50microgram increments at three to four week intervals until normal metabolism is maintained indicated by the clinical response, plasma thyroxine and thyroid stimulating hormone levels.
Maintenance dose: 100micrograms to 200micrograms daily.
Diffuse non toxic goitre or goitre associated with Hashimoto's thyroiditis
50micrograms to 200micrograms daily.
Suppression therapy in thyroid carcinoma
150micrograms to 300micrograms daily.
Some brands recommend an initial dose of 12.5micrograms which should then be increased slowly and at lengthy intervals (e.g. a gradual increment of 12.5micrograms a day fortnightly) in the elderly, in patients with coronary heart disease and in patients with severe or long-existing hypothyroidism.
Children
Children's dosage is guided by clinical response, growth assessment, appropriate thyroid function tests to ascertain plasma thyroxine level and until thyroid stimulating hormone levels suggest the thyroid deficiency is corrected.
Acquired hypothyroidism
Initial dose: 12.5micrograms to 50micrograms daily 30 minutes before breakfast.
Initial dose is then increased gradually every two to four weeks according to the clinical findings and thyroid hormone and TSH values until the full replacement dose is reached.
The maintenance dose is generally 100micrograms/metre squared to 150micrograms/metre squared body surface area.
Congenital hypothyroidism
Initial dose: 10micrograms/kg to 15micrograms/kg daily for the first three months.
The maintenance dose is generally 100micrograms/metre squared to 150micrograms/metre squared body surface area.
Juvenile myxoedema (Not all brands licensed)
Initial dose: 25micrograms daily, then increased by 25micrograms every two to four weeks until mild toxic symptoms appear. Dosage should then be slightly reduced.
The following alternative dosing schedule may be suitable:
Hypothyroidism
Children aged 12 to 18 years
Initial dose: 50micrograms once daily. Adjust in steps of 25micrograms to 50micrograms every three to four weeks until metabolism normalised.
Maintenance dose: 100micrograms to 200micrograms daily.
Children aged between 2 and 12 years
Initial dose: 50micrograms once daily. Adjust in steps of 25micrograms every two to four weeks until metabolism normalised.
Maintenance dose: 75micrograms to 100micrograms daily.
Children aged between 1 month and 2 years
Initial dose: 5 micrograms/kg daily (maximum 50 micrograms daily). Adjust in steps of 10micrograms to 25micrograms every two to four weeks until metabolism normalised.
Maintenance dose: 25micrograms to 75micrograms daily.
Infants should be given the total daily dose at least half an hour before the first meal of the day.
Neonates
Initial dose: 10micrograms/kg to 15micrograms/kg daily for the first three months. Thereafter, the dose should be adjusted individually according to the clinical findings and thyroid hormone and TSH values.
The following alternative dosing schedule may be suitable:
Initial dose: 10micrograms/kg to 15 micrograms/kg daily (maximum 50micrograms per dose). Adjust in steps of 5micrograms/kg every two weeks or as necessary.
Maintenance dose: 20micrograms to 50micrograms daily.
Contraindications
Thyrotoxicosis
Uncontrolled adrenal insufficiency
Precautions and Warnings
Patients over 50 years
Adrenal insufficiency
Breastfeeding
Cardiovascular disorder
Diabetes insipidus
Diabetes mellitus
Epileptic disorder
Galactosaemia
Glucose-galactose malabsorption syndrome
Hypertension
Lactose intolerance
Pituitary insufficiency
Pregnancy
Severe prolonged hypothyroidism
Corticosteroid cover required in adrenal insufficiency
Severe or long standing hypothyroidism - introduce treatment gradually
Low weight preterm neonate: Monitor haemodynamic parameters
Not all available brands are licensed for all indications
Oral solution contains glycerol
Oral solution contains parabens: Potential for delayed allergic reactions
Some formulations contain lactose
Monitor closely if switching between tablet formulation and oral solution
Consider ECG before treatment
Monitor thyroid function prior to and periodically during pregnancy
Diabetic control may need adjustment
Monitor digoxin levels in digitalised patients at start of treatment
Monitor thyroid function clinically and biochemically
Reduce or suspend treatment if metabolic rate increase is too rapid
Soya products may impair absorption- monitor and adjust dose if needed
Advise patient that alopecia may occur
Advise patient to seek advice at first indications of pregnancy
Maintain treatment at the lowest effective dose
Avoid antacids and mineral supplements within 4 hours of dose
Take at least 30 minutes before breakfast and caffeine-containing products
Note that if an increase in the metabolic rate is produced too rapidly, diarrhoea, nervousness, rapid pulse, insomnia, tremors or anginal pain (if latent ischaemia) may result. In such cases, reduce the dose or withdraw treatment for one to two days and re-introduce at a lower dose.
If secondary hypothyroidism occurs, the cause must be identified prior to replacement therapy and if necessary, replacement treatment of a compensated adrenal insufficiency must be initiated.
If thyroid autonomy is suspected, a TRH test could be undertaken or a suppression scintigram obtained prior to treatment.
Treatment with levothyroxine should be used with caution in patients with cardiovascular disorders including myocardial insufficiency and hypertension, and must not be initiated in acute myocardial infarction, acute myocarditis and acute pancarditis.
Special care is needed when symptoms of or ECG evidence of myocardial insufficiency occurs.
Drug-induced hyperthyroidism must be avoided in patients with coronary failure, cardiac insufficiency or tachycardiac arrhythmias. Frequent measures of thyroid hormone parameters should be carried out in these patients.
Caution should be used when initiating treatment of hypothyroidism in elderly.
Monitor serum TSH and adjust dose accordingly during long term use to minimise risk of adverse effects of undetected overtreatment.
Monitor haemodynamic parameters in low weight preterm neonates due to possible circulatory collapse from immature adrenal function.
Thyroid hormones are not suitable in aiding weight loss. Supraphysiological doses in euthyroid patients may cause severe or even life-threatening effects.
Pregnancy and Lactation
Pregnancy
Use levothyroxine with caution in pregnancy.
Women who become pregnant whilst on a maintenance dose should be monitored closely.
Levothyroxine does not readily cross the placental barrier during the second and third trimesters but may during the first. There are no known carcinogenic or teratogenic effects, but excessive maternal concentrations of levothyroxine can be detrimental to the foetus.
Treatment with levothyroxine should be given consistently during pregnancy and breastfeeding in particular. Maternal levothyroxine dosage should be monitored as requirements may change during pregnancy. Dosage requirements may even increase during pregnancy. Possible risk of foetal abnormalities should be weighed against the risk to the foetus of untreated hypothyroidism.
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.
Thyroid suppression diagnostic tests should not be carried out during pregnancy, as the application of radioactive substances in pregnant women is contraindicated.
Lactation
Use levothyroxine with caution in breastfeeding.
Substitution of thyroid hormones establishes a physiological state and therefore should be continued during breastfeeding.
Monitor mother and infant closely.
Levothyroxine is a normal component of human milk. Minimal concentrations of the drug are secreted in the breast milk which may mask hypothyroidism in a newborn baby. There is insufficient thyroid hormone in breast milk to meet the needs of a suckling infant with a non-functioning thyroid gland. Limited data on exogenous replacement doses of levothyroxine during breastfeeding indicate no adverse effects in infants.
Levothyroxine dosage requirement may be increased in the postpartum period compared to pre-pregnancy requirements patients with Hashimoto's thyroiditis (Lactmed, 2021).
Side Effects
Agitation
Alopecia (transient)
Angina pectoris
Anginal pain
Angioedema
Arrhythmias
Arthralgia
Benign intracranial hypertension
Craniostenosis
Decrease in bone mineral density
Diarrhoea
Dyspnoea
Eosinophilia
Excitability
Flushing
Headache
Heat intolerance
Hypersensitivity reactions
Insomnia
Joint pain
Liver function disturbances
Malaise
Menstrual disturbances
Muscle spasm
Muscle weakness
Muscular cramps
Nervousness
Oedema
Palpitations
Premature closure of epiphyses
Pruritus
Pyrexia
Rash
Restlessness
Seizures
Sweating
Tachycardia
Thyroid crisis
Tremor
Urticaria
Vomiting
Weight loss
Overdosage
It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.
The following number will direct the caller to the relevant local centre (0844) 892 0111
Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Further Information
Last full review: December 2018
Reference Sources
Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 3rd edition (2015) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.
Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 10th edition (2015) ed. Briggs, G., Freeman, R. Wolters Kluwer Health, Philadelphia.
Summary of Product Characteristics: Eltroxin 25 mcg Tablets. ADVANZ Pharma Limited. Revised December 2019.
Summary of Product Characteristics: Eltroxin 50 micrograms. ADVANZ Pharma Limited. Revised December 2019.
Summary of Product Characteristics: Eltroxin 100 micrograms. ADVANZ Pharma Limited. Revised December 2019.
Summary of Product Characteristics: Levothyroxine Tablets BP 50 micrograms. Accord-UK Ltd. Revised June 2020.
Summary of Product Characteristics: Levothyroxine Tablets BP 100 micrograms. Accord-UK Ltd. Revised June 2020.
Summary of Product Characteristics: Levothyroxine 125 micrograms/5ml oral solution. Creo Pharma Limited. Revised April 2019.
Summary of Product Characteristics: Levothyroxine 12.5 microgram Tablets. Teva UK Limited. Revised July 2018.
Summary of Product Characteristics: Levothyroxine 25 micrograms Tablets. Wockhardt UK Ltd. Revised April 2018.
Summary of Product Characteristics: Levothyroxine 75 microgram Tablets. Teva UK Limited. Revised July 2018.
Summary of Product Characteristics: Levothyroxine 25 micrograms/5ml Oral Solution. Wockhardt UK Limited. Revised September 2018.
Summary of Product Characteristics: Levothyroxine 50 micrograms/5ml Oral Solution. Wockhardt UK Limited. Revised September 2018.
Summary of Product Characteristics: Levothyroxine 100 micrograms/5ml Oral Solution. Wockhardt UK Limited. Revised September 2018.
Summary of Product Characteristics: Levothyroxine 75 micrograms/5ml Oral Solution. Brillpharma Ltd. Revised April 2021.
NICE Evidence Services Available at: www.nice.org.uk Last accessed: 12 December 2018
US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
Available at: https://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT
Levothyroxine. Last revised: 21 June 2021.
Last accessed: 02 September 2021.
Medscape UK | Univadis prescription drug monographs & interactions are based on FDB Multilex Content
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