Drugs for Thyroid Disorders Flashcards
Drugs for hypothyroidism and hyperthyroidism
Name the most common autoimmune cause of hypothyroidism. How does this disorder result in hypothyroidism?
Hashimoto’s thyroiditis (also known as Hashimoto’s disease). Autoantibodies against thyroid gland proteins, typically against thyroid peroxidase (TPO), trigger inflammation of the thyroid gland and chronically impair the production of thyroid hormones.
What is the first line drug for chronic hypothyroidism?
Levothyroxine. Levothryoxine replaces T4 and is converted to the approximately 1000-fold more active T3 in the liver, by gut microflora (including on enterohepatic recirculation), and in many target tissues and organs.
What advice should the patient be given on when to take levothyroxine?
Take levothyroxine once per day on an empty stomach 30 min to 1 hour before food. As the stomach is usually most empty after overnight fasting, it is usually taken before breakfast.
Why is it important to take levothyroxine on an empty stomach?
Oral bioavailability is decreased by many drug-food and drug-drug interactions.
List common foods and drugs that interfere with absorption of levothryoxine.
Wait 1 hour before taking food, soya milk, coffee, or bulk-forming laxatives. Wait 4 hours before taking iron or calcium supplements or antacids.
Why is it important to continue to administer the same brand of levothyroxine?
Oral bioavailability is highly variable (from 40% to 80%) between different manufacturers’ formulations. It is therefore best to keep using the same brand once an appropriate dose has been titrated, especially as the long half-life means that it takes a month or longer to reach a new steady state when the dose absorbed changes.
What is the half-life of levothyroxine?
6 to 8 days
How long does it take to reach steady state after changing the dose of levothyroxine?
About 4 to 6 weeks (least 5 x the half-life of 6 to 8 days).
What are the adverse effects of overdose of levothryoxine?
Cardiac arrest, hypertension, palpitations, tachycardia, anxiety, heat intolerance, hyperactivity, insomnia, irritability and weight loss. In children, overdosing can cause insomnia, restlessness, accelerated growth and bone maturation.
How fast is the onset of clinical action of levothyroxine?
Oral: 1-3 days; IV: 6-8 hours.
Due to the long half-life, it usually takes 1-3 weeks of daily dosing for plasma levels to accumulate sufficiently to see clinical improvement on first treatment. It takes 3-4 weeks of daily dosing to approach steady-state and achieve peak action.
How fast is the onset of clinical action of liothyronine?
Oral: 2-4 hours; IV: immediate. Liothyronine replaces T3, which is approximately 1000-fold more potent than T4.
Why is liothyronine not routinely used for treatment of chronic hypothyroidism?
Liothyronine (replacing T3) has a much faster onset of action than levothyroxine (replacing T4) and is much more potent. Liothyronine, therefore, has a markedly higher acute risk of adverse cardiovascular events (e.g., cardiac arrhythmia, tachycardia, and even myocardial infarction).
When is liothyronine usually administered?
Liothyronine has a much faster onset of action than levothyroxine and so is the drug of choice for intravenous administration in myxoedema coma due to severe untreated hypothyroidism.
What is the first line drug for chronic hyperthyroidism?
Carbimazole.
What is the active metabolite of carbimazole?
Thiamazole. Thiamazole (known as methimazole) can itself be used for the treatment of
hyperthyroidism but carbimazole is usually preferred here as it has a longer clinical duration of action due to the combined half-life of the pro-drug (carbimazole) and its active metabolite (thiamazole).
