Formulary
Levothyroxine sodium: Indications, Dosing, Side Effects and Interactions
Levothyroxine sodium clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 4 min read
Levothyroxine sodium: Indications, Dosing, Side Effects and Interactions
Levothyroxine sodium clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Primary hypothyroidism**
- **Adult** (By Mouth): Initially 1.6 micrograms/kg once daily, adjusted according to response, round dose to the nearest 25 micrograms, dose to be taken preferably 30-60 minutes before breakfast, caffeine-containing liquids (e.g. coffee, tea), or other medication.
- **Elderly** (By Mouth): Initially 25-50 micrograms once daily; adjusted in steps of 25 micrograms every 4 weeks, adjusted according to response; maintenance 50-200 micrograms once daily, dose to be taken preferably 30-60 minutes before breakfast, caffeine-containing liquids (e.g. coffee, tea), or other medication.
**Primary hypothyroidism in patients with cardiac disease**
- **Adult** (By Mouth): Initially 25-50 micrograms once daily; adjusted in steps of 25 micrograms every 4 weeks, adjusted according to response; maintenance 50-200 micrograms once daily, dose to be taken preferably 30-60 minutes before breakfast, caffeine-containing liquids (e.g. coffee, tea), or other medication.
**Hyperthyroidism (blocking-replacement regimen) in combination with carbimazole**
- **Adult** (By Mouth): 50-150 micrograms daily therapy usually given for 18 months.
**Hypothyroidism for levothyroxine sodium**
- **Neonate** (By mouth): Initially 10-15 micrograms/kg once daily (max. per dose 50 micrograms); adjusted in steps of 5 micrograms/kg every 2 weeks, alternatively adjusted in steps of 5 micrograms/kg as required; maintenance 20-50 micrograms daily, levothyroxine should be taken at the same time each day, preferably 30-60 minutes before meals, caffeine-containing drinks, or other medicines; this could be before breakfast or another more convenient time.
- **Child 1 month-1 year** (By mouth): Initially 5 micrograms/kg once daily (max. per dose 50 micrograms); adjusted in steps of 10-25 micrograms every 2-4 weeks until metabolism normalised; maintenance 25-75 micrograms daily, levothyroxine should be taken at the same time each day, preferably 30-60 minutes before meals, caffeine-containing drinks, or other medicines; this could be before breakfast or another more convenient time.
- **Child 2-11 years** (By mouth): Initially 50 micrograms once daily; adjusted in steps of 25 micrograms every 2-4 weeks until metabolism normalised; maintenance 75-100 micrograms daily, levothyroxine should be taken at the same time each day, preferably 30-60 minutes before meals, caffeine-containing drinks, or other medicines; this could be before breakfast or another more convenient time.
- **Child 12-17 years** (By mouth): Initially 50 micrograms once daily; adjusted in steps of 25-50 micrograms every 3-4 weeks until metabolism normalised; maintenance 100-200 micrograms daily, levothyroxine should be taken at the same time each day, preferably 30-60 minutes before meals, caffeine-containing drinks, or other medicines; this could be before breakfast or another more convenient time.
**Hyperthyroidism (blocking-replacement regimen) in combination with carbimazole for levothyroxine sodium**
- **Child** (By mouth): Therapy usually given for 12 to 24 months (consult product literature or local protocols).
Cautions
Cardiovascular disorders; diabetes insipidus; diabetes mellitus (dose of antidiabetic drugs including insulin may need to be increased); elderly; hypertension; long-standing hypothyroidism; myocardial infarction; myocardial insufficiency; panhypopituitarism (initiate corticosteroid therapy before starting levothyroxine); predisposition to adrenal insufficiency (initiate corticosteroid therapy before starting levothyroxine) Cautions, further information Cardiovascular disorders Baseline ECG is valuable because changes induced by hypothyroidism can be confused with ischaemia.
Contraindications
Thyrotoxicosis
Side effects
General side-effects: Common or very common Anxiety; arrhythmias; headache; insomnia; palpitations Frequency not known Angina pectoris; diarrhoea; fever; flushing; hyperhidrosis; menstruation irregular; muscle weakness; skin reactions; tremor; vomiting; weight decreased Specific side-effects: Common or very common With parenteral use Hyperthyroidism Rare or very rare With parenteral use Idiopathic intracranial hypertension (particularly in children) Frequency not known With oral use Alopecia; arthralgia; dyspnoea; malaise; muscle spasms; oedema; thyrotoxic crisis With parenteral use Angioedema; heat intolerance; muscle cramps; nausea Side-effects, further information If metabolism increases too rapidly following initial dosage (causing diarrhoea, nervousness, rapid pulse, insomnia, tremors and sometimes anginal pain where there is latent myocardial ischaemia), reduce dose or withhold for 1-2 days and start again at a lower dose.
Interactions
**Other interactions (15):**
- Interactions affecting other drugs: Levothyroxine increases the effect of anticoagulants (Warfarin) and it may be necessary to reduce the anticoagulation dosage if excessive, hypoprothrombinaemia...
- Hyperthyroid patients may need their digoxin dosage gradually increased as treatment proceeds because initially patients are relatively sensitive to digoxin.
- 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 tri iodothyronine resulting in a decreased concentration of tri iodothyronine, thereby reducing the...
- Anti-convulsants, such as carbamazepine and phenytoin, enhance the metabolism of thyroid hormones and may displace them from plasma proteins.
Pregnancy
Levothyroxine may cross the placenta. Excessive or insufficient maternal thyroid hormones can be detrimental to fetus. Levothyroxine requirement may increase during pregnancy. Monitoring in pregnancy Assess maternal thyroid function before conception (if possible), at diagnosis of pregnancy, at antenatal booking, during both the second and third trimesters, and after delivery (more frequent monitoring required on initiation or adjustment of levothyroxine).
Breast feeding
Amount too small to affect tests for neonatal hypothyroidism.
Medicinal forms
Capsule,Tablet,Capsule,Solution
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
Inside MedNext for this topic
- 411 MedNext-authored chapters
- 80,000+ MCQ bank
- 15 study modes
- Growing visual cheat sheets
Study modes
- Notes
- MCQ
- Audio
- Video
- Visual
- 3D Anatomy
- Trace
- Flashcards
- Mnemonics
- Image Bank
- Clinical
- Microscopy
- Audio QBank
- Cadaver
- Book Match
Continue reading
Subject HubPharmacology Hub
All pharmacology resources in one place.
Drug SchedulesIndian Drug Schedules
Schedule H, H1, X and G classifications.
FormularyBrowse all drugs
Search 1,850+ drug profiles.
Study Levothyroxine sodium in the MedNext app
Challenge yourself with targeted pharmacology MCQs on this drug class. Every explanation links back to the chapter that teaches the concept.
Start drug challengeExplore the full formulary