FR Review 2 - Thyroid, DM, and Weight Loss Flashcards
What are the 2 thyroid hormones and what is their relationship?
L-thyroxine (T4) and Liothyronine (T3). T4 is the precursor to T3 which is the active hormone.
Describe the hypothalamic-pituitary-thyroid axis.
Hypot releases TRH –> AP releases TSH –> thyroid releases T4 –> T4 deiodinated to T3 in periphery.
How is the majority of T3 and T4 present in the blood?
Bound to plasma protein (inactive) –> thyroxine binding globulin (TBG)
What increases and decreases TBG?
Inc: pregnancy and oral contraceptives
Dec: anabolic steroids (T inc metabolic requirements which increases need for free T3)
State and describe the drug most used to treat hypothyroid.
Levothyroxine (T4, aka Synthroid) –> slow on and slow off. Max effect of one dose reached in 10 days.
What lab value indicates hypothyroidism (cretinism)?
High TSH, low T3 and T4
What is the dosing regimen for hypothyroidism?
50-100 mcg synthroid qd titrated up to normal TSH
In dosing synthroid what considerations are given to pregnant females and to cardiac patients?
pregnant: need higher dose (TBG increases)
cardiac: need lower dose (don’t overstimulate heart)
Why is synthroid taken on an empty stomach?
Synthroid sticks to food, dec absorption
T/F: Hyperthyroid disease is much easier to treat than hypothyroid disease.
False –> hypothyroid easy to manage by titrating Synthroid. Hyperthyroid often involves surgical removal of the thyroid gland.
What is the mechanism of action of methimazole?
Blocks formation of thyroid hormones by inhibiting oxidation of dietary iodine. Does not block conversion ot T4 to T3.
What is the mechanism of action of propylthiouracil (PTU) and why are its effects delayed?
Inhibits oxidation of thyroid hormone. Max effects not seen until all previously formed T4/T3 is exhausted.
Why is a high dose of PTU the treatment of choice in thyroid storm?
PTU blocks peripheral conversion of T4 to T3
Other than PTU, what 2 medications are the ideal treatment of thyroid storm?
IV or PO propranolol –> non-selective beta blocker
High dose dexmethasone –> inhibit T4 - T3 conversion (monitor BGL in Pt’s on dexmethasone)
When in pregnancy is PTU preferred over methimazole?
During the 1st trimester –>PTU still crosses blood-placenta barrier and may enter breast milk.
Does iodine cause hypothyroidism or hyperthyroidism?
Can cause either
What is the purpose of giving radioactive iodine?
Iodine goes straight to the thyroid, taking the radiation with it to destroy thyroid tissue. This is used to treat hyperthyroidism.
Differentiate TID from T2D.
T!D: inability to produce insulin
T2D: Down regulation of insulin receptors and desensitization of insulin receptors s/p poor diet, lack of exercise, and obesity.
What is the general rule for dosing insulin and where do you start for a new patient?
1 unit of insulin used per kg of body weight. Start a new patient at 80% of daily use then titrate PRN.
What is the main drug that induces hyperglycemia? List some others that cause hyperglycemia.
1 - steroids. Others - glucagon, epi, thyroid hormones, oral contraceptives, HCTZ/diuretics (mild increase)
List and describe the insulins in each category of formulation.
Immediate: Lispro - closest to regular insulin
Short: regular insulin - quick on, quick off
Intermediate: NPH - administered BID
Long: Detemir and Glargine - administered QD
Describe the initial insulin dosing regimen for a new T1D patient.
Start with conventional insulin BID - 2/3 dose in the morning and 1/3 at bedtime - with q6h BGL checks
What does it mean for insulin to be “70/30”?
70% long acting agent (NPH) and 30% short acting agent (Lispro) in one vial. The first number is always indicative of the longer acting insulin’s percentage
Why is an insulin syringe rolled rather than shaken to mix the suspension?
Shaking denatures the proteins causing foam formation.
