What do I do if I accidentally take a high dose of thyroxine (T4)?

From the Guidelines

If you accidentally take a high dose of thyroxine (T4), you should immediately contact your healthcare provider or poison control center for guidance, as the effects of an overdose can be serious and potentially life-threatening, particularly affecting the heart. When managing patients with thyroxine overdose, it's crucial to consider the dose and the patient's overall health status. According to the most recent guideline update 1, for patients without risk factors, full replacement can be estimated, but in the case of an overdose, this principle does not apply directly. Instead, monitoring for symptoms such as rapid heart rate, chest pain, anxiety, tremors, headache, sweating, and in severe cases, heart rhythm problems, is essential.

While the provided study 1 primarily focuses on the management of immune-related adverse events and mentions thyroxine dosing in the context of replacement therapy, the key takeaway for accidental overdose is the importance of prompt medical evaluation. The study suggests that for certain patients, such as those older than 70 years or frail patients with multiple comorbidities, lower starting doses of thyroxine are considered to avoid overtreatment, highlighting the need for cautious management of thyroxine levels.

In the event of an overdose, do not attempt to induce vomiting or take any additional doses of thyroxine unless instructed by a healthcare professional. Be prepared to provide detailed information about the overdose, including the amount taken and the time it was taken, to medical staff. Given that thyroxine regulates metabolism and an overdose can lead to overstimulation of the body's systems, particularly the heart, immediate medical attention is critical, even if symptoms are not immediately apparent.

Key considerations in managing thyroxine overdose include:

• Immediate contact with a healthcare provider or poison control center
• Monitoring for symptoms of overdose
• Avoidance of additional thyroxine doses or self-induced vomiting without medical instruction
• Prompt medical attention to prevent potential serious complications, especially cardiac issues.

From the FDA Drug Label

OVERDOSAGE The signs and symptoms of overdosage are those of hyperthyroidism (see PRECAUTIONS and ADVERSE REACTIONS). In addition, confusion and disorientation may occur. Cerebral embolism, shock, coma, and death have been reported. Seizures have occurred in a child ingesting 18 mg of levothyroxine Symptoms may not necessarily be evident or may not appear until several days after ingestion of levothyroxine sodium. Treatment of Overdosage Levothyroxine sodium should be reduced in dose or temporarily discontinued if signs or symptoms of overdosage occur Acute Massive Overdosage - This may be a life-threatening emergency, therefore, symptomatic and supportive therapy should be instituted immediately. If not contraindicated (e.g., by seizures, coma, or loss of the gag reflex), the stomach should be emptied by emesis or gastric lavage to decrease gastrointestinal absorption. Activated charcoal or cholestyramine may also be used to decrease absorption. Central and peripheral increased sympathetic activity may be treated by administering β-receptor antagonists, e.g., propranolol, provided there are no medical contraindications to their use. Provide respiratory support as needed; control congestive heart failure and arrhythmia; control fever, hypoglycemia, and fluid loss as necessary. Large doses of antithyroid drugs (e.g., methimazole or propylthiouracil) followed in one to two hours by large doses of iodine may be given to inhibit synthesis and release of thyroid hormones. Glucocorticoids may be given to inhibit the conversion of T 4 to T 3. Plasmapheresis, charcoal hemoperfusion and exchange transfusion have been reserved for cases in which continued clinical deterioration occurs despite conventional therapy. Because T 4 is highly protein bound, very little drug will be removed by dialysis.

If you accidentally take a high dose of thyroxine (T4), it is considered a life-threatening emergency. The following steps should be taken:

• Reduce or discontinue the dose of thyroxine (T4) if signs or symptoms of overdosage occur.
• Symptomatic and supportive therapy should be instituted immediately.
• Stomach emptying by emesis or gastric lavage may be necessary to decrease gastrointestinal absorption.
• Activated charcoal or cholestyramine may be used to decrease absorption.
• β-receptor antagonists (e.g., propranolol) may be administered to treat increased sympathetic activity.
• Respiratory support, control of congestive heart failure and arrhythmia, and management of fever, hypoglycemia, and fluid loss may be necessary.
• In severe cases, antithyroid drugs, iodine, glucocorticoids, plasmapheresis, charcoal hemoperfusion, and exchange transfusion may be considered 2.

From the Research

Accidental High Dose of Thyroxine (T4)

If an individual accidentally takes a high dose of thyroxine (T4), it is essential to understand the potential risks and management strategies.

• The toxic dose of levothyroxine is unclear, but asymptomatic patients have been observed with doses under 5 mg 3.
• Symptoms of levothyroxine overdose may appear from hours to days after ingestion and can affect the cardiovascular system, sympathetic nervous system, and gastrointestinal tube 3.
• In cases of overdose, monitoring of seric levels of T3, T4, and TSH is necessary to guide therapeutic approach and prognosis 3.
• Daily determinations of temperature, arterial pressure, and blood heart rate are also needed to control complications 3.
• Beta-blockers and intestinal decontamination drugs may be used during therapeutic approach, and other options include iopanoic acid and propylthiouracil 3.

Management of Levothyroxine Overdose

• Expect significant toxicity in children and adults who have ingested more than 2 to 4 mg of levothyroxine, although the threshold may be lower in comorbid elderly patients 4.
• In cases of levothyroxine overdose, asymptomatic clinical course may be related to coingestion of benzodiazepines, beta-blockers, ACE inhibitors, and ethanol 4.
• Serum free triiodothyronine (T3) levels can be elevated after an overdose of levothyroxine, with normalization observed over time 4.
• The adverse effects of levothyroxine are signs of thyrotoxicosis in case of overdose, including tachycardia, tremor, sweating, and others 5.
• Even a slight overdose carries a risk of osteoporotic fractures and atrial fibrillation, especially in the elderly 5.