Pharmacology 2 Block 3- Thyroid
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Created by:
robinsonjb on October 28, 2011
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64 terms
Terms | Definitions |
|---|---|
 Role/ utilization of iodine in the thyroid | -Iodine is added to a tyrosine residue to create the hormones released by the thyroid -T4 has 4 iodines -T3 has 3 iodines |
| Synthesis thyroid hormones | -Iodine can increase production of the hormones when found in the diet -Iodine can decrease production of the hormones when given pharmacologically |
| Transport of thyroid hormones... | must be done by transporter proteins |
| Metabolism and conversion of thyroid hormones | -T4 is converted to T3 by 5'-deiodinase to T3 which enters the nucleus where it binds to a specific T3 receptor protein which leads to an increased formation of RNA and subsequent protien synthesis |
| Which thyroid hormone is more prevalent? | T4 |
| Which thyroid hormone is more potent | T3 |
| What medication class can be used to halt conversion of T4 to T3 and to treat thyroid storms | Beta blockers |
| Where is T4 best absorbed? | Duodenum and ileum where it is about 80% absorbed |
| How well is T3 absorbed? | 95% absorbed |
| Drugs that induce microsomal enzymes will do what to the metabolism of T4 and T3 | Increase |
| Starvation does what to circulating T3 hormones and cellular T3 receptors | Lowers |
| What does a decrease in T3 early in life result in? | Dwarfism and mental retardation |
| T3's action on development and functioning of nervous, skeletal, and reproductive tissue depends on what? | Protein synthesis and secretion of GH |
| Thyroid receptors bind to what? | Thyroid response elements found on DNA in the promotor/ regulatory regions and then activates the TRE which starts transcription |
| Which two genes encode thyroid receptors | THRA and THRB |
| What does THRA encode for and what does it regulate? | TR alpha 1 which regulates heart rate, body temperature, skeletal muscle function, and development of bone and small intestine |
| What does THRB encode for? | two promotors that lead to production of TRB1 and TRB2 which have unique amino terminal domains but the rest of the molecules are identical |
| TRB1 is involved with what? | Liver metabolism |
| TRB2 is involved with what? | development of cones in the retina & inner ear development- negative feedback loop by T3 on hypothalamic TRH and pituitary TSH |
| Effects of T3 | -Tadpole to frog -Vasodilation, brain development, growth, and thermogenesis |
| Hypothyroidism causes what? | Bradycardia, decreased cardiac index, pericardial infusion, increased pericardial vascular resistance, decreased pulse pressure, & increased arterial pressure |
| Hyperthyroidism causes what? | Tachycardia, increased stroke volume, increased cardiac index, cardiac hypertrophy, decreased peripheral vascular resistance, & increased pulse pressure |
| What does TH do to hepatic LDL receptors? | Increases their expression and increases the metabolism of cholesterol to bile salts |
| What is the most common disorder of thyroid function? | hyothyroidism (myxedema) which can be caused by an iodine deficiency or chronic automiimune thyroiditis (Hashimoto's)- antibodies against thyroid peroxidase adn against thyroglobulin |
| Primary hypothyroidism | Failure of the thyroid gland |
| Central hypothyroidism | Decreases stimulation of the thyroid by TSH becuase of pituitary failure or hypothalamic failure |
| What are the symptoms of hypothyroidism? | Fatigue, lethargy, col intolerance, mental slowness, depression, dry skin, constipation, mild weight gain, fluid retention, muscle aches & stiffness, irregular menses, and infertility |
| Hyperthyroidism causes what? | -Increased levels of free TH found in serum -also called thyrotoxicosis |
| What is Graves' disease? | -Most common cause of high RAIU -Autoimmune disorder that causes an increase in TH production, diffuse goiter, & IgG antibodies that bind & activate the TSH receptor -In caucasians, major histocompatibility alleles (HLA) B8 & DR3 are associated |
| What are the symptoms of hyperthyroidism? | Excessive heat production, increased motor activity, increased to catecholamines produced by sympathetic nervous system, flush/warm/moist skin, weak/tremulous muscles, rapid heart rate, increased appetite due to more energy being expended, loss of weight, insomnia, and heat intolerance |
| What symptoms are seen more in elderly? | Angina, arrythmias, & heart failure |
| Which symptoms are seen less in elderly? | Less incidence of sympathetic nervous system stimulation- apathetic hyperthyroidism |
| What drugs are L-T4 preparations? | Levothroid, levoxyl, synthroid, and unithroid |
| Where are levothyroxine sodium preps absorbed? | Stomach and small intestine (80%) but is absorbed more on an empty stomach and is associated with less variability in the TSH when taken like this on a regular basis |
| When do serum TSH levels peak for levothyroxine preps? | 2-4 hours after oral ingestion |
| What is the half-life of levothyroxine sodium? | 7 days |
| What are the potency standards for levothyroxine standards? | 95-105% which has been decreased from 90-110% |
| Levothyroxine raises what serum ratio? | T4/T3 because 20% of circulating T3 is supplied by direct thyroidal secretion |
| When do you need to check serum levels for thevothyroxine? | ~6 weeks because of the half life of 7 days |
| What is the equivalent dose for L-T4 oral and injectable? | Injectable dose is 80% of oral dose |
| What drugs are L-T3 preparations? | Cytomel (tablets) Triostat (injection) |
| What is the absorption of L-T3? | 100% with peak serum levels 2-4 hours following oral ingestion |
| Which has a more rapid onset of action L-T4 or L-T3? | L-T3 and requires more frequent dosing |
| What is the half-life of L-T3? | 18 hours |
| Is L-T4 desirable for chronic dosing? | No because the transient levels of serum T3 increase above normal levels |
| What dose of L-T3 yields normal serum levels of T3 in athyreotic individuals? | 10-15 mcg |
| Does the dose of L-T3 need to be changed when a patient's TSH is low? | Yes, because of the negative feedback normally requires local generation of T3 from circulating T4 |
| What drug is a preparation that includes T4 & T3? | Thyrolar (Iotrix) 4 (T4): 1 (T3) |
| What drug has a similar ratio of T4:T3? | Desiccated thyroid (Armour thyroid) |
| What dose of Armour thyroid is equivalent to thyroxine? | 60mg (1 grain) Armour thyroid to 80mcg of thyroxine |
| What is the mechanism of action for antithyroid drugs? | Interfere directly with the synthesis of thyroid hormone by not allowing iodine to be added to tyrosine residues |
| What is the mechanism of action for ionic inhibitors? | Block the iodide transport mechanism |
| What is the mechanism of action for iodine? | High concentrations of iodine decrease the release of thyroid hormones from the gland and may also decrease the synthesis of hormones |
| What is the mechanism of action for radioactive iodine? | Damages the thyroid gland with ionizing radiation |
| What family do the antithyroid drugs belong to? | Thionamides |
| What is the prototypical antithyroid drug? | Propylthiouracil |
| Propylthiouracil MOA | does the same as other antithyroid drugs but also inhibits the peripheral deiodination of T4 to T3 |
| What is propylthiouracil used for? | thyroid storm an d severe hyperthyroidism |
| What is the most severe ADR for antithyroid drugs? | Agranulocytosis |
| What is the most common ADR for antithyroid drugs? | purpuric, urticarial papular rash |
| What are other ADRs of antithyroid drugs? | Pain, stiffness in the joints, parasthesis, HA, nausea, skin pigmentation, and loss of hair |
| What is the black box warning for propylthiouracil? | associated hepatic failure (mainly in children and pregnant women) |
| What is methimazole's main ADR? | Cholestatic dysfunction |
| What are the ADRs for the iodides? | acneiform rash, swollen salivary glands, mucous membrane ulcerations, conjunctivitis, rhinorrhea, drug fever, metallic taste, bleeding disorders, and anaphylactiod reaction |
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