Thyroid drugs

Question 1

Hypothyroidism

Answer 1

Increased TSH

Decreased T4 and T3, or conversion issue (T4 –> T3)

Question 2

Hyperthyroidism

Answer 2

Decreased TSH
Increased T4 and T3
Drugs (plus beta blockers) tx thyroid storm (catecholamine-like state)

Question 3

T4

Answer 3

Thyroid hormone Thyroxine 
Converted into T3
Present in greater quantities than T3
Longer 1/2 life (7 d)
Pro-hormone/low potency

Question 4

T3

Answer 4

Thyroid hormone Triiodothyronine
Present in lesser quantities than T4
Shorter 1/2 life (1 d)
3-4X more potent than T4
Acts like a catecholamine

Question 5

Thyroid hormone synthesis

Answer 5

Get iodide from diet --> 
Iodide converted into iodine --> 
Iodine + tyrosine (amino acid) = T4 --> 
T4 converted into T3 (in periphery)
The end

Question 6

Levothyroxine

Answer 6

Hypo tx - “Gold standard”
Synthetic T4 - body will store and convert to T3 in ratios
Take on empty stomach - needs acidic pH for absorption
Takes awhile to reach “steady state” (4-6 wks)
Narrow therapeutic index so requires monitoring
Boxed warning: not for tx of obesity/not for weight loss
Acute AE: thyroid storm/thyrotoxic crisis (hyper-like state)
LT AE: dysrhythmia (a-fib)

Question 7

Liothyronine

Answer 7

Hypo tx
Synthetic T3 - when someone has issues converting T4 into T3, or T4 tx insufficient
Boxed warning: not for tx of obesity/not for weight loss
Acute AE: thyroid storm/thyrotoxic crisis (hyper-like state)
LT AE: dysrhythmia (a-fib)

Question 8

Desiccated animal thyroid

Answer 8

Hypo tx
Natural animal thyroid (pigs?)
Provides T3 and T4, but ratios different from human ratios
Also provides T1, T2, calcitonin
NOT recommended as a tx by professional associations

Question 9

Methimazole

Answer 9

Hyper tx - “First line therapy”
Prevents creation of thyroid hormone (prevents conversion of iodide to iodine, prevents coupling of iodine + tyrosine)
AEs: hepatotoxicity, agranulocytosis (dangerously low WBCs)

Question 10

Hypothyroidism tx for preg/lactating women

Answer 10

Recommendation is:
Take PTU for 1st trimester (poorly crosses placenta)
Then take Methimazole for 2nd and 3rd trimesters (to prevent fetal abnormalities)
Low doses OK for breastfeeding

Question 11

PTU

Answer 11

Hypo tx
Superior to Methimazole in thyroid storm - take w/beta blocker during crisis to protect heart
Prevents creation of thyroid hormone (prevents conversion of iodide to iodine, prevents coupling of iodine + tyrosine), PLUS prevents conversion of T4 –> T3
AEs: hepatotoxicity, agranulocytosis (dangerously low WBCs)

Question 12

Thyroid Storm

Answer 12

AKA thyrotoxic crisis
Hyper-like, catecholamine-like state
Result of untreated or undertreated hyper, or serious AE of hypo drugs
HR, BP, and body temp soar to dangerously high levels
Tx w/PTU