Synthroid Uses, Dosage & Side Effects

Data for this retrospective cohort study were obtained from claims contained in the HealthCore Integrated Research Database (HIRD®). Data are derived from a large national commercial payer with membership in all 50 US states. Because of the increased prevalence of cardiovascular disease among the elderly, initiate SYNTHROID at less than the full replacement dose see DOSAGE AND ADMINISTRATION and WARNINGS AND PRECAUTIONS. If you become pregnant while taking Synthroid, do not stop taking the medicine without your doctor’s advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine.

Adverse Reactions In Pediatric Patients

Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease.
Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentration.
Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.
Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with SYNTHROID see CONTRAINDICATIONS.
Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism.
Since postpartum TSH levels are similar to preconception values, the SYNTHROID dosage should return to the pre-pregnancy dose immediately after delivery see Dosage and Administration (2.3).

Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants. Synthroid is also used in patients who need surgery and radioiodine therapy to manage a type of thyroid cancer called well-differentiated thyroid cancer. Synthroid is a prescription medicine used to treat hypothyroidism (low thyroid hormone). Levothyroxine is given when your thyroid does not produce enough of this hormone on its own. The major transdermal synthroid pathway of thyroid hormone metabolism is through sequential deiodination. Approximately 80% of circulating T3 is derived from peripheral T4 by monodeiodination.

Levothyroxine has a narrow therapeutic window, and slight variations in dose or differences in bioavailability between products can impact clinical effectiveness 8–10. Previous real-world research using administrative claims data demonstrated differences in outcomes between patients with hypothyroidism treated with Synthroid or GL 9, 10. Compared with patients who received GL, significantly fewer patients in the Synthroid treatment group had TSH levels outside the recommended range (0.3 to 4.12 mIU/L) and a smaller proportion was undertreated 9, 10. Secondary outcomes included all-cause and hypothyroidism-related healthcare resource utilization (HCRU) and costs. All-cause HCRU and costs included all medical and pharmacy claims, and costs were the sum of plan-paid and patient-paid amounts.

Data Availability

Titrate the dosage (every 2 weeks) as needed based on serum TSH or free-T4 until the patient is euthyroid see Dosage and Administration (2.2). All patients were ≥ 18years old on the index date, and all had at least 6 months of pre-index (baseline) and 12 months of post-index (follow-up) health plan enrollment. Patients were required to have at least 1 TSH laboratory result during the 12-month follow-up period and be persistent in their index therapy through follow-up. In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. In patients on a stable and appropriate replacement dosage, evaluate clinical and biochemical response every 6 to 12 months and whenever there is a change in the patient’s clinical status. Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%.

The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues. Biotin supplementation is known to interfere with thyroid hormone immunoassays that are based on a biotin and streptavidin interaction, which may result in erroneous thyroid hormone test results. Stop biotin and biotin-containing supplements for at least 2 days prior to thyroid testing. He or she may want to test yourthyroid levels to determine if any adjustment needs to be made to your dose or to the wayyou’re taking Synthroid. Levoxyl treats hypothyroidism (low thyroid hormone) and treats or prevents goiter. Do not store the crushed tablet/water mixture and do not administer it mixed with foods that decrease absorption of levothyroxine, such as soybean-based infant formula.

Utilization and Costs at Follow-Up

To minimize the risk of hyperactivity, start at one-fourth the recommended full replacement dosage, and increase on a weekly basis by one-fourth the full recommended replacement dosage until the full recommended replacement dosage is reached. At baseline, hospitalizations and ED visits were rare (6–8% all-cause), while most patients in both cohorts had outpatient visits and pharmacy fills (94–99% all-cause), with mean number of all-cause pharmacy fills per patient of 9.2–9.3. Total all-cause costs were approximately $5800–6000 per patient in 2017 USD (Table 2). Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins.

Symptoms may not necessarily be evident or may not appear until several days after ingestion of levothyroxine sodium. Serum TSH levels should be monitored and the SYNTHROID dosage adjusted during pregnancy. Since postpartum TSH levels are similar to preconception values, the SYNTHROID dosage should return to the pre-pregnancy dose immediately after delivery see DOSAGE AND ADMINISTRATION. Administer SYNTHROID to pediatric patients who cannot swallow intact tablets by crushing the tablet, suspending the freshly crushed tablet in a small amount (5 to 10 mL) of water and immediately administering the suspension by spoon or dropper.

Cardiac Adverse Reactions In The Elderly And In Patients With Underlying Cardiovascular Disease

SYNTHROID may reduce the therapeutic effects of digitalis glycosides. Serum digitalis glycoside levels may decrease when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides. Titrate the dose of SYNTHROID carefully and monitor response to titration to avoid these effects see Dosage and Administration (2.4).

Patient Characteristics

Toxic effects may include increased risk of cardiac arrhythmias and central nervous system stimulation. Administration of sertraline in patients stabilized on SYNTHROID may result in increased SYNTHROID requirements. Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in pediatric patients receiving levothyroxine therapy. Carefully monitor glycemic control after starting, changing, or discontinuing SYNTHROID see Drug Interactions (7.2). Over-treatment with levothyroxine may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients. Initiate SYNTHROID therapy in this population at lower doses than those recommended in younger individuals or in patients without cardiac disease see Dosage and Administration (2.3) and Use in Specific Populations (8.5).

The liver is the major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including the kidney and other tissues. Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (rT3). Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.