Thyroid and Antithyroid Drug Therapy

• Cretinism: Associated with childhood, characterized by low BMR, retarded physical/sexual development, and mental delays.
• Myxedema: Characterized by loss of mental/physical stamina, weight gain, firm edema, and a yellow dullness of the skin.

Thyroid Replacement: Levothyroxine

The gold standard for treating hypothyroidism is Levothyroxine, a synthetic or natural T4 replacement. Its mechanism involves increasing the metabolic rate, protein, carbohydrate, and lipid metabolism, and increasing the number of myocardial beta-adrenergic receptors to boost cardiac output.

Clinical Pearl: Administration Levothyroxine must be taken on an empty stomach with water early in the morning, 30–60 minutes before food. If the patient uses a G-tube, hold tube feedings for 30–60 minutes prior to administration to prevent impaired absorption.

Contraindications and Interactions: Levothyroxine is contraindicated in patients with hyperthyroidism, recent myocardial infarction, or adrenal insufficiency. It also has significant drug interactions:

• Warfarin: Increases bleeding risk.
• Digoxin: May decrease digoxin levels.
• Oral Hypoglycemics: May reduce blood glucose control.
• Absorption Inhibitors: Phenytoin, calcium, iron, and estrogen can reduce levothyroxine levels.

Hyperthyroidism: When Metabolism Accelerates

Hyperthyroidism is characterized by high levels of T3 and T4 and low TSH. The most common cause is Grave’s disease, an autoimmune condition. Other causes include thyroid nodules or excessive iodine intake.

Symptoms reflect a hypermetabolic state: tachycardia, palpitations, weight loss, heat intolerance, tremors, and exophthalmos (bulging eyes).

The Emergency: Thyroid Storm

A rare but life-threatening complication of hyperthyroidism is Thyroid Storm. This is caused by a massive, sudden increase in T3 and T4 levels, often triggered by extreme stress or infection. Patients present with high fever, extreme anxiety, and severe tachycardia. This is a medical emergency requiring immediate hospitalization.

Antithyroid Therapy: Propylthiouracil (PTU)

To treat hyperthyroidism, clinicians use antithyroid drugs like Propylthiouracil (PTU). PTU is a thioamide derivative that inhibits hormone production by blocking iodine. It is also used to prevent thyroid storm following surgery or radioactive iodine treatment.

Cautions and Adverse Effects: PTU is classified as Category D in pregnancy; however, it is often preferred during the first trimester, after which patients may switch to methimazole. Key adverse effects include:

• Bone marrow suppression: Monitor CBC closely.
• Gastrointestinal issues: Nausea, vomiting, and diarrhea.
• Liver/Renal impact: Monitor liver enzymes and BUN/creatinine.

Nursing Plan of Care

A comprehensive nursing plan must address both the physiological monitoring and the patient's education regarding long-term medication adherence.

Assessment and Monitoring

• Lab Values: Periodically check TSH, T3, and T4 levels to adjust dosages.
• Hypothyroidism Monitoring: Watch for signs of overdosage (tachycardia, palpitations, insomnia, weight loss).
• Hyperthyroidism Monitoring: Assess for signs of infection (due to bone marrow suppression risk) and manifestations of thyroid storm.
• Older Adults: Start with lower doses of levothyroxine and increase slowly, as they are more sensitive to drug effects.

Patient Education

1. Consistency: For hypothyroidism, treatment is often lifelong; do not stop hormone replacement. Do not switch brands of levothyroxine.
2. Dietary Restrictions: Patients on PTU should avoid iodized salt and other iodized foods.
3. Symptom Reporting: Teach patients to report signs of infection immediately (for PTU users) or signs of hyperthyroidism (for levothyroxine users).

Exam Tip: Differentiating Symptoms If a patient on levothyroxine presents with sudden weight loss, tremors, and heat intolerance, they are likely experiencing overdosage (symptoms of hyperthyroidism).