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Thyroid Hormone Pregnancy: The safety of levothyroxine treatment during pregnancy is not known, but any 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. Levothyroxine is excreted in breast milk in low concentrations.

Levothyroxine (Elderly)

Brand names: Eltroxin, Euthyrox

Used in: Thyroid Disorders

This page covers levothyroxine in older patients, the synthetic thyroid hormone (T4) used to treat hypothyroidism; in this group cautious initiation protects against cardiac effects.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Patients over 50 years of age (SPC states the elderly are the same as patients aged over 50): without cardiac disease — initially it is not advisable to exceed 50 micrograms daily; with cardiac disease — 25 micrograms daily, or 50 micrograms on alternate days
Route: Oral
Frequency: Once daily, preferably taken before breakfast or the first meal of the day
Max: In patients over 50 years the final daily dose may be up to 50 to 200 micrograms
Titration in patients over 50 years: without cardiac disease, increase the daily dose by 50 micrograms at intervals of every 3-4 weeks until stable thyroxine levels are attained; with cardiac disease, increase by 25 micrograms at intervals of every 4 weeks. For patients aged over 50, with or without cardiac disease, clinical response is probably a more acceptable criterion of dosage than serum levels. Patients under 50 years without heart disease: initially 100 micrograms daily, adjusted at three to four week intervals by 50 micrograms until normal metabolism is steadily maintained; final daily dose may be up to 100 to 200 micrograms. In younger patients without heart disease, target a serum T4 of 70 to 160 nanomol/litre or a serum thyrotrophin below 5 milli-units/litre. A pre-therapy ECG is valuable because ECG changes due to hypothyroidism may be confused with ECG evidence of cardiac ischaemia; in individuals suspected of, or at high risk of, cardiovascular disease perform an ECG before starting and initiate at a low dose with cautious escalation. If too rapid an increase in metabolism is produced (diarrhoea, nervousness, rapid pulse, insomnia, tremors, and sometimes anginal pain where there is latent cardiac ischaemia), the dose must be reduced or withheld for a day or two and then restarted at a lower dose level. Levothyroxine should be introduced very gradually in patients aged over 50 and those with long-standing hypothyroidism. Monitor serum TSH and adjust the dose during long-term use to minimise undetected overtreatment (risk of atrial fibrillation and fractures in older patients). Thyroid replacement may increase requirements for insulin or other antidiabetic therapy. The SPC also gives separate paediatric posology, including weight-based dosing for congenital hypothyroidism in neonates and infants — verify any paediatric dosing against a children's formulary. Note: eMC §4.5 (interactions) was not captured in this source bundle; the interactions listed below are taken from the US prescribing information.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Thyrotoxicosis
  • Adrenal gland disorder or adrenal insufficiency
  • Treatment must not be initiated in acute myocardial infarction, acute myocarditis or acute pancarditis
  • Combination therapy of hyperthyroidism with levothyroxine and anti-thyroid agents is not indicated in pregnancy

Side effects

  • Angina pectoris, arrhythmia, palpitations, tachycardia
  • Restlessness, agitation, insomnia
  • Tremor
  • Diarrhoea, vomiting
  • Hyperhidrosis, alopecia, rash, pruritus; headache, pyrexia, malaise, oedema, weight decreased

Interactions

  • Phosphate binders (e.g. calcium carbonate, ferrous sulfate, sevelamer, lanthanum) may bind levothyroxine — administer at least 4 hours apart (US label §7.1)
  • Bile acid sequestrants (e.g. colesevelam, cholestyramine, colestipol) and ion exchange resins decrease levothyroxine absorption (US label §7.1)
  • Orlistat — monitor patients treated concomitantly for changes in thyroid function (US label §7.1)
  • Administer levothyroxine at least 4 hours before or after drugs known to interfere with its absorption; evaluate the need for dose adjustment when regularly administering within one hour of certain foods (US label §2.1)
  • Biotin and biotin-containing supplements — advise patients to stop at least 2 days before assessing TSH and/or T4 levels (US label §2.2, §7.10)
  • Insulin and other antidiabetic therapy (such as metformin) — thyroid replacement may increase dosage requirements; monitor glycaemic control (SPC §4.4)

Clinical monograph

How it works

It is converted to active triiodothyronine (T3) and restores physiological thyroid hormone levels, normalising metabolic rate and tissue function.

Prescribing in practice

  • In older patients, and especially those with ischaemic heart disease, start at a low dose and titrate slowly, as rapid correction can precipitate angina, arrhythmia or myocardial ischaemia.
  • Take on an empty stomach and apart from interacting agents such as calcium and iron salts, which impair absorption; consistent timing relative to food and other drugs is important.
  • Over-replacement risks atrial fibrillation and accelerated bone loss, both of particular concern in older people.

Monitoring

Monitor thyroid function (TSH, with free T4) some weeks after initiation or dose changes and periodically thereafter, allowing time to reach steady state.

Counselling the patient

  • Take at the same time each day, usually before food, and separately from calcium or iron supplements.
  • Report palpitations, chest pain, tremor or unexpected weight change.
  • Do not change the dose yourself; adjustments are guided by blood tests.

Evidence & guidelines

UK thyroid guidance recommends low starting doses and gradual titration of levothyroxine in older patients and those with cardiac disease to avoid precipitating ischaemic events.

Reference: BTA/NICE guidelines; RCP guidance 2019; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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