Module 8: Drugs for Thyroid Disorder

Question 1

Thyroid Function Tests

Answer 1

Serum thyroid-stimulating hormone (TSH)
 Screening and diagnosis of hypothyroidism
 Elevated TSH is an indicator of hypothyroidism

Serum T4 test
 Can measure total T4 or free T4
Serum T3 test
 Can measure total T3 or free T3

Question 2

Hypothyroidism

Answer 2

Severe deficiency of thyroid hormone
 Myxedema (adults)
* Replacement therapy with thyroid hormones; in almost all cases, treatment must continue lifelong
* Hypothyroidism during pregnancy
* To help ensure healthy fetal development, maternal
hypothyroidism must be diagnosed and treated very early
 Congenital hypothyroidism (infancy)
* Replacement therapy with thyroid hormones

Question 3

Hypothyroidism in Adults

Answer 3

Clinical presentation
 Pale, puffy face
 Cold, dry skin
 Brittle hair or loss of hair
 Lowered heart rate and temperature
 Lethargy and fatigue
 Intolerance to cold
 Impaired mentality

Causes
 Usually due to malfunction of the thyroid
 Hashimoto’s disease: Chronic autoimmune thyroiditis
 Insufficient iodine in the diet
 Surgical removal of thyroid and destruction of thyroid with radioactive iodine
 Insufficient secretion of TSH and thyrotropin-releasing hormone (TRH)

Treatment
Therapeutic strategy
 Lifelong replacement therapy
 Levothyroxine (T4)
 Liothyronine (T3)

Question 4

Hypothyroidism: Life Span Issues

Answer 4

During pregnancy
 In first trimester can result in permanent
neuropsychologic deficits in the child

In infants
 May be permanent or transient
 Can cause intellectual disability and derangement of
growth

Question 5

Hyperthyroidism

Answer 5

Two Forms of Hyperthyroidism

Graves’ disease
 Most common form
 Affects women age 20 to 40 years
 Causes exophthalmos (Exophthalmos, also known as proptosis, is a medical condition characterized by a noticeable protrusion of one or both eyeballs from the eye sockets (orbits)

Toxic nodular goiter (Plummer’s disease)

Cause
 Thyroid-stimulating immunoglobulins (TSIs)

Treatment
 Surgical removal of thyroid tissue
 Destruction of thyroid tissue
 Suppression of thyroid hormone synthesis
 Beta blockers (eg, propranolol)
 Nonradioactive iodine

Question 6

Thyrotoxic Crisis (Thyroid Storm)

Answer 6

Cause
 Patients with thyrotoxicosis who undergo significant
stress (eg, surgery, illness)
 Not triggered by a rise in thyroid hormones
 Cannot be identified by laboratory testing

Signs
 Hyperthermia (105F or higher), severe tachycardia,
restlessness, agitation, tremor, unconsciousness,
coma, hypotension, heart failure

Treatment
 Methimazole
 Beta blocker
 Sedation, cooling, glucocorticoids, IV fluid

Question 7

Thyroid Hormone Preparations

Answer 7

Levothyroxine [Synthroid]
 Synthetic preparation of thyroxine (T4) and drug of
choice for hypothyroidism
 Conversion to T3
 Half-life: 7 days
 Used for all forms of hypothyroidism

Should be taken in the morning at least 30 to 60
minutes before breakfast
 Adverse effects
* Tachycardia
* Angina
* Tremors
* Can intensify effects of warfarin

Drug interactions
* Drugs that reduce levothyroxine absorption
* Drugs that accelerate levothyroxine metabolism
* Warfarin
* Catecholamines

Other thyroid preparations
 Liotrix [Thyrolar]
 Thyroid (Armour Thyroid, others

Question 8

Hyperthyroidism: Methimazole

Answer 8

First-line drug for hyperthyroidism
 Prototype of the thionamides
 Does not cause the liver damage associated with
propylthiouracil (PTU)
 Does not destroy existing stores of thyroid hormone
 May take 3 to 12 weeks for euthyroid state
 More dangerous than PTU during lactation and
during the first trimester of pregnancy
 Agranulocytosis

Four applications in hyperthyroidism:
 Sole form of therapy for Graves’ disease
 Adjunct to radiation therapy until the effects of
radiation become manifest
 Suppresses thyroid hormone synthesis in preparation for thyroid gland surgery (subtotal thyroidectomy)
 Thyrotoxic crisis

Question 9

Propylthiouracil (PTU)

Answer 9

Inhibits thyroid hormone synthesis
 Second-line drug for Graves’ disease
 Short half-life (about 90 minutes)
 Full benefits may take 6 to 12 months

Therapeutic uses
 Graves’ disease
 Adjunct to radiation therapy
 Preparation for thyroid gland surgery
 Thyrotoxic crisis

Adverse effects
 Agranulocytosis (most serious)
 Hypothyroidism
 Pregnancy and lactation
 Can cause severe liver damage

Question 10

PTU Versus Methimazole

Answer 10

PTU can cause severe liver injury, whereas
methimazole does not
 PTU has a shorter half-life than methimazole (90
minutes compared to 6 to 13 hours), so it requires
two or three daily doses rather than one
 PTU crosses the placenta less readily than does
methimazole, and concentrations in breast milk are
lower
 PTU blocks conversion of T4 to T3 in the periphery,
whereas methimazole does not

Question 11

Radioactive Iodine-131 (131I)

Answer 11

Radioactive isotope of stable iodine
 Emits gamma and beta rays
 Half-life: 8 days
 2 to 3 months for full effect
 Used in Graves’ disease
 Effect on the thyroid
 Advantages and disadvantages of 131I therapy

Question 12

Nonradioactive Iodine

Answer 12

Strong iodine solution (Lugol’s solution)
 Used to suppress thyroid function in preparation for
thyroidectomy

 Adverse effects
* Brassy taste
* Burning sensation in the mouth and throat
* Soreness of the teeth and gums
* Frontal headache
* Coryza
* Salivation
* Various skin eruptions