Synthroid Levothyroxine Sodium: Side Effects, Uses, Dosage, Interactions, Warnings

Seizures occurred in a 3-yearold child ingesting 3.6 mg of levothyroxine. Symptoms may not necessarily be evident or may not appear until several days after ingestion of levothyroxine sodium. The general aim of therapy is to normalize the serum TSH level.

Side Effects for Synthroid

Thyroid hormones do not readily cross the placental barrier see Use In Specific Populations. The signs and symptoms of overdosage are those of hyperthyroidism see WARNINGS AND PRECAUTIONS and Adverse Reactions. Cerebral embolism, shock, coma, and death have been synthroid edema reported.

Table 2:

However, in many reports repeated doses of activated charcoal were ineffective in accelerating the elimination of levothyroxine, probably due to high uptake in the duodenum and jejuno-ileum. If more than a few hours of ingestion of LT-4 tablets have elapsed, most probably the tablets have travelled from the gastric cavity to duodenum. Moreover, gastric lavage is difficult to conduct in small children.

TSH may not normalize in some patients due to in utero hypothyroidism causing a resetting of pituitary-thyroid feedback. Assess compliance, dose of medication administered, and method of administration prior to increasing the dose of SYNTHROID see WARNINGS AND PRECAUTIONS and Use In Specific Populations. The recommended starting daily dosage of SYNTHROID in pediatric patients with primary, secondary, or tertiary hypothyroidism is based on body weight and changes with age as described in Table 2.

• Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Synthroid only for the indication prescribed.
• Medicines that interact with Synthroid may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Synthroid.
• Eltroxin is used for hashimoto’s disease, hypothyroidism, after thyroid removal, myxedema coma …
• Children can take the medicine if the tablet is crushed and put into about 1 to 2 teaspoons of water; do not store or delay giving this crushed pill suspension.
• Symptoms of levothyroxine overdose include irregular heartbeat, headache, anxiety, agitation, shaking, fatigue, confusion, and disorientation.

Laboratory workup usually reveals elevated serum total T4 and T3, suppressed serum TSH, and elevated Free T4 and Free T3. A massive L-Thyroxine (T4) overdose may be accidentally and unintentionally ingested, most commonly by children and adolescents. It may occur intentionally in young and older adults in an attempt to lose weight, with suicidal intentions, or for undeclared purposes. In some localities thyroxine may be obtained at drugstores without prescription (mostly in the generic form). In some reports thyroxine preparations by a pharmacist had an erroneous LT4 dosage.

• Toxic effects may include increased risk of cardiac arrhythmias and central nervous system stimulation.
• Monitor for cardiac arrhythmias during surgical procedures in patients with coronary artery disease receiving suppressive SYNTHROID therapy.
• Most probably LT-4 would not be entirely dissolved by the gastric juice and may not be absorbed in the duodenum (normally about 10-15%) but would be absorbed in the jejuno-ileum (normally about 53% of absorption of LT4).

Clinical Pharmacology for Synthroid

Patients with massive exposures or ingestion of T3-containing preparations should be admitted in anticipation of pending toxicity. Chronic thyroxine excess is more likely to cause clinically important thyrotoxicosis, and is particularly concerning in the elderly and those with cardio-respiratory comorbidities. The doctor wants to know the best way of managing this patient’s impending “thyrotoxic storm”.

Poisoned?

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. Levothyroxine toxicity is rare; however, it is most likely to occur in the setting of accidental ingestion by children or older adults. Thyroxine (T4) and triiodothyronine (T3) levels rise within 1 to 2 hours of ingestion. In the initial stage of overdose (6 to 12 hours post-ingestion), the common signs of toxicity would be tremulousness, tachycardia, hypertension, anxiety, and diarrhea. Rarely convulsions, thyroid storms, acute psychosis, arrhythmias, and acute myocardial infarction may occur.

What to do if someone takes too much levothyroxine or takes it by accident

Acute levothyroxine overdose is much more common in children compared to adolescents and adults. Therapeutic options are related to the time elapsed after the ingestion of a large number of tablets of L-thyroxine and the actual beginning of emergency therapy (Table 3). Acute massive doses of L-thyroxine typically have a mild clinical course that can be controlled by activated charcoal, or possibly cholestyramine, propranolol, dexamethasone, and supporting measures, with close medical evaluation. Rarely critical cardiac conditions, coma, seizures will follow massive doses of L-Thyroxine. Levothyroxine is an oral medication used to treat underactive thyroid gland activity (hypothyroidism).

It may take several weeks before your body starts to respond to Synthroid. Some brands of levothyroxine have different dosage instructions and/or recommendations of how soon you need to take them before eating food. Taking more than your recommended dose will not make this medicine more effective, and may cause serious side effects.

In one report total serum T3 levels reached the normal range five days after ingestion of 9.9 mg of LT4 (99 tablets of 100 mcg), although free T4 levels were still elevated. In many cases, there is a progressive rise in both serum total T4 and total T3 levels in the first 24 hours following the overdose, caused by continued absorption of the ingested LT4. Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%. The majority of the SYNTHROID dose is absorbed from the jejunum and upper ileum. The relative bioavailability of SYNTHROID tablets, compared to an equal nominal dose of oral levothyroxine sodium solution, is approximately 93%.