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19 terms

Thyroid

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DOC for Tx of hypothyroidism in all species
levothyroxine (T4)
Liothyronine (T3)
Faster onset of action; shorter 1/2 life; more potent; may cause thyrotoxicosis
Used in dogs with intestinal malabsorption because it is more readily absorbed
Liothyronine (T3)
May be used in animals treated with glucocorticoid
Liothyronine (T3)
Tx of thyrotoxicosis
withdrawing the drug, beta blockers, and activated charcoal
Levothyroxine (T4)
allows for intracellular autoregulation and provides T3
Species in which commercial combinations of T4 to T3 (4:1) are not recommended
dogs
Tx of myxyedema coma in dogs
L-thyroxine sodium for injection IV or SC; warming the animal; artificial respiration; fluid, electrolytes, glucocorticoids for shock
Drugs that decrease thyroid levels
glucocorticoids, sulfonamides, anticonvulsants, phenylbutazone, salicylates, quinidine, mitotane, general anesthetics
Antithyroid drugs
thioureylenes (methimazole, propylthiouracil), iodides (lugol's iodine, potassium iodide), iodinated radiographic contrast agents (ipodate), antithyroid plants (cabbage, turnip, broccoli, and rapeseed)
MOA thioureylenes
inhibit synthesis of thyroid hormones by inhibiting organification and coupling
MOA iodides
inhibit thyroid hormone organification, inhibit preformed hormone secretion, reduce the size and vascularity of the thyroid gland, may inhibit the binding of iodine
MOA iodinated radiographic contrast agents
inhibits conversion of T4 and T3 in peripheral tissues, inhibit thyroid hormone synthesis and release
MOA antithyroid plants
contain goitrin which inhibits thyroid hormone synthesis
Tx of hyperthyroidism in cats
sx thyroidectomy, radioactive iodine, antithyroid drugs, beta blockers
Radioactive iodine therapy
selectively destroys thyroid tissue; has a 1/2 life of 8 days; treated cats must be hospitalized for 1-4 wks; can produce a premanent cure w/o sx; also used for thyroid adenocarcinoma; very safe, but very expensive
Antithyroid DOC in the cat
methimazole
Adverse effects of methimazole
anorexia, vomiting, lethargy, hepatic toxicity, blood disorders
Used for at large doses for a short period of time before sx to stabilize the patient
oral iodide therapy