Pharmacology Quiz 2: drugs for thyroid disorders, diabetes,

Thyroid feedback loop?

-Low T3 and T4 hormone stimulates hypothalamus and pituitary

-Increased T3 and T4 hormone inhibits hypothalamus and pituitary

-Negative feedback loop!

-Low TH levels = higher levels of TRH and TSH

Thyroid hormone?

-Stimulates energy use

-Stimulates the heart

-Promotes growth and development

Hypothyroidism?

-Deficient thyroid hormone

-Needs lifelong treatment

Symptoms: fatigue, weight gain, muscle weakness, brain fog, constipation, brittle dry hair, depression, anxiety, numbness in hands

Levothyroxine (Synthroid)?

-Synthetic T4, identical to natural TH

-Does not make thyroid hormone but it itself acts as the thyroid hormone

-Given PO on empty stomach (30 to 60 minutes before breakfast)

-IV form available

-Given once daily

-Half life is 1 week

-Takes about 1 month to reach plateau and to feel symptom relief

-Usually give in IV form to achieve plateau faster if patient is very symptomatic

Levothyroxine (Synthroid) adverse effects?

-Osteoporosis (supplement calcium for at risk patients)

-AFIB

-Thyrotoxicosis (too much T3 and T4)

Levothyroxine (Synthroid) absorption decreased by...

-Calcium

-Magnesium

-Iron

-Antacids

-H2 blockers and proton pump inhibitors

-Cholesterol binding agents

-Food

Separate dose by 4 hours from drugs that interact

Levothyroxine (Synthroid) absorption increased by...

-Phenytoin

-Rifampin

-Carbamazepine

-Warfarin (Coumadin)

How does Levothyroxine (Synthroid) interact with Warfarin (Coumadin)?

-Warfarin is a blood thinner

-They do not go well together

-Levothyroxine (Synthroid) makes Warfarin act weirdly and increases effects, making blood extremely thin

How does Levothyroxine (Synthroid) interact with insulin and digoxin?

Levothyroxine (Synthroid) can increase the requirements for both drugs

How does Levothyroxine (Synthroid) interact with Catecholamines?

-Catecholamines include epinephrine, dopamine, and dobutamine

-Levothyroxine (Synthroid) increases the responsiveness of catecholamines

-Use cautiously

Is Levothyroxine (Synthroid) safe to use during pregnancy?

-Is a category A drug

-Drug does pass in breast milk but is considered safe to use

-Need to increase dose during pregnancy

Pediatric use of Levothyroxine (Synthroid)?

-Continue through age 3

-Stop for 4 weeks to see if hypothyroidism is transient or permanent

Hyperthyroidism?

-Excessive thyroid hormone secretion

-"Graves disease"

-Medications for hyperthyroidism can be problematic, so some people opt to remove the thyroid gland

Symptoms: intolerance to heat, bulging eyes, enlarged thyroid, weight loss, tachycardia, diarrhea, tremors, finger clubbing

Methimazole (Tapazole)?

-Used to treat hyperthyroidism

-First drug used to try and treat

-Inhibits thyroid hormone synthesis

-Does not destroy existing stores of thyroid hormone

-Can take 3 to 12 weeks to develop a plateau

-Taken orally

Methimazole (Tapazole) adverse effects?

-Avoid in first trimester of pregnancy, teratogenic

-May induce hypothyroidism (reduce dose)

-Can cause agranulocytosis (severely low levels of WBC's, report fever or sore throat immediately)

Propylthiouracil (PTU)?

-Used to treat hyperthyroidism

-Inhibits thyroid hormone synthesis

-Generally not preferred over Methimazole (Tapazole)

-Preferred during a thyrotoxic crisis

-Preferred during 1st trimester of pregnancy, does not cross placenta as easily

-Has a shorter half life, requires multiple doses per day

Propylthiouracil (PTU) adverse effects?

-Can cause agranulocytosis

-Risk of liver injury (death and liver transplants have been reported)

Radioactive iodine?

-Used for hyperthyroidism (low dose), thyroid cancer (high dose), or to test for thyroid disorders

-Absorbed by thyroid and destroys its cells

-Contradicted in pregnant, lactating, and pediatric patients

-Limit contact with other people while in use

Beta blockers?

-Can be used to help treat hyperthyroidism

-Decrease heart rate and other symptoms of graves disease

-Blocks beta receptors in heart

-Also may be used in a thyrotoxic crisis

-Contradicted in patients with asthma