Thyroid scintigraphy I-123 Radiology Reference Article

In all the scenarios mentioned above, pharmacists should ensure proper dosing and report to the clinician if there is any potential drug-drug interaction or if supplies may dictate a change to a different formulation. In addition, many drugs and foods affect T4 absorption see Drug Interactions (7). Dosage titration is based on serum TSH or free-T4 see Dosage and Administration (2.2). In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage.

Does levothyroxine interact with my other drugs?

This list is not complete and many other drugs may interact with levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines. Concurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline) antidepressants and SYNTHROID may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines.

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. Carefully monitor glycemic control, especially when thyroid therapy is synthroid cardiotoxic started, changed, or discontinued see Warnings and Precautions (5.5).

• If so, advise them to stop biotin supplementation at least 2 days before assessing TSH and/or T4 levels.
• Note the position and mark palpable nodules and surgical scars.
• The major pathway of thyroid hormone metabolism is through sequential deiodination.

STARTING DOSE CALCULATOR FOR ADULTS

Start at a lower starting dosage and increase the dosage every 4 to 6 weeks as needed based on clinical and laboratory response. The importance of writing “Dispense as Written,” or using the state-specific language for SYNTHROID, is something I discuss with my staff as well. The FDA has determined that drugs that are classified as therapeutically equivalent can be substituted with the full expectation that the substituted product will produce the same clinical effect and safety profile as the reference product. Particularly when SYNTHROID is written in a non-protective manner for the state language. Most, but not all, levothyroxine products have been determined to be therapeutically equivalent by the FDA. Dosing here should be individualized based on whether the patients were diagnosed with hypothyroidism prior to pregnancy or during the pregnancy.

Do not administer in foods that decrease absorption of SYNTHROID, such as soybean-based infant formula see DRUG INTERACTIONS. Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. However, you may not be able to take this medicine if you have certain medical conditions. Levothyroxine belongs to a class of medications called hormones.

• Use the drop-down menu below to select your state and see the specific language required to prevent generic substitution.
• Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur.
• Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%.
• Do not stop taking this medicine or change your dose without first checking with your doctor.

Synthroid During Pregnancy and Breastfeeding

Thyroid hormones do not readily cross the placental barrier see Use in Specific Populations (8.1). Because of the increased prevalence of cardiovascular disease among the elderly, initiate SYNTHROID at less than the full replacement dose see Dosage and Administration (2.3) and Warnings and Precautions (5.2). Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly. Published studies report that levothyroxine is present in human milk following the administration of oral levothyroxine.

• There are certain foods that can interfere with the way SYNTHROID works, particularly we think about high-fiber foods that can interact with the absorption of thyroid medications.
• Serum TSH levels should be monitored and the SYNTHROID dosage adjusted during pregnancy.
• Employ the following treatment approach in acute levothyroxine overdose.
• The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Consumption of certain foods may affect SYNTHROID absorption thereby necessitating adjustments in dosing see DOSAGE AND ADMINISTRATION. 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. Synthroid should not be used to treat obesity or weight problems.

HYPOTHYROIDISM MEDICATION1,2*

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 a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body’s energy and metabolism. Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of this medicine, especially if you are taking any other weight-loss medications or appetite suppressants.

Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. This medicine is also used to help decrease the size of enlarged thyroid glands (also called a goiter). Levothyroxine is also used together with surgery and radioiodine treatment to treat a type of thyroid cancer called thyroid-dependent well-differentiated thyroid cancer. Assess compliance, dose of medication administered, and method of administration prior to increasing the dose of SYNTHROID see Warnings and Precautions (5.1) and Use in Specific Populations (8.4). SYNTHROID is indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. Assess compliance, dose of medication administered, and method of administration prior to increasing the dose of SYNTHROID.

Drugs That May Decrease T4 Absorption (Hypothyroidism)

It works by replacing thyroid hormone that is normally produced by the body. Levothyroxine is used in adults and children to treat hypothyroidism (underactive thyroid – a condition where the thyroid gland does not produce enough thyroid hormone). The “optimal dose” was determined for each patient as that dosage of thyroxine being taken when the thyrotropin-releasing hormone (TRH) response was normal (ie, an increase in TSH of between 4.7 and 25 mIU/L). The signs and symptoms of overdosage are those of hyperthyroidism see Warnings and Precautions (5) and Adverse Reactions (6). Seizures occurred in a 3-year-old child ingesting 3.6 mg of levothyroxine. Titrate the dose of SYNTHROID carefully and monitor response to titration to avoid these effects see Dosage and Administration (2.4).