3 Thyroid Medications
Learn how levothyroxine, methimazole, and propylthiouracil are used, administered, monitored, and managed when adverse effects or pregnancy require prompt clinical review.
use and absorption
replaces thyroid hormone in hypothyroidism. It should be taken consistently on an empty stomach, 30–60 minutes before breakfast. Food and medicines such as calcium and iron can reduce absorption, so separate calcium from by at least 4 hours.
If thyroid tests are outside the target range, do not adjust treatment based on symptoms alone. Changes in the use of calcium, iron, or other interacting medicines may alter absorption, thyroid test results, and dose requirements.
monitoring and possible excess
’s full effect takes several weeks. For primary hypothyroidism, is commonly reassessed about 4–6 weeks after a dose change; thyroid tests should also be rechecked after a change in how the medicine is administered. Further dose adjustments are guided by laboratory results and clinical context.
New palpitations, tremor, or heat intolerance may indicate excessive thyroid hormone replacement. Review the dose, adherence, and interacting medicines, and assess thyroid function before changing treatment.
and causes of hyperthyroidism
reduces new thyroid hormone synthesis and is commonly used for hyperthyroidism due to Graves’ disease. Treatment depends on the cause of abnormal thyroid tests: a low alone does not establish that is appropriate.
releases stored hormone from an inflamed gland. Antithyroid drugs such as do not treat this process.
Monitoring antithyroid treatment and urgent blood symptoms
Follow thyroid hormone levels and clinical status to assess response and guide dose adjustments. may remain suppressed for some time after treatment begins, so it may not reflect the early response by itself. Free T4, and sometimes T3, can help assess response during this period.
Fever or severe sore throat while taking an antithyroid medicine may indicate , a rare but potentially life-threatening reduction in white blood cells. Seek prompt medical assessment, typically including a blood count, and contact the prescriber before taking further doses. The treating clinician should advise whether to hold or restart the medicine.
PTU risks and liver warning signs
can cause severe, sometimes fatal, liver injury. It is generally not the default antithyroid drug, but may be selected when antithyroid treatment is needed in the first trimester of pregnancy because has a different risk profile for fetal development. The choice of treatment and any later change require clinician oversight.
Promptly report symptoms that may indicate liver injury, including jaundice, dark urine, or itching. Fever or severe sore throat during antithyroid treatment also requires prompt attention.
Pregnancy and antithyroid medicines
Pregnancy requires individualized management of antithyroid treatment because both uncontrolled hyperthyroidism and medication exposure can affect the pregnancy. When antithyroid treatment is needed during the first trimester, PTU is generally preferred. Anyone taking who becomes pregnant should promptly contact the treating clinician to review the treatment plan rather than continuing unchanged or stopping treatment without advice.