nsc 830 thyroid - eastern kentucky university · 2015-08-13 · 8/12/2015 1 nsc 830: drugs...

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NSC 830: Drugs

Affecting the Thyroid BROOKE BENTLEY, PHD, APRN

Hypothalamus-Pituitary-Thyroid Hormone Axis

� TSH: Normal = 0.5-5 mU/L

� Free T4: 1.3-3.8 ng/dL

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Hypothyroidism: Thyroid

Agents

� Natural

� Health food stores: dessicated thyroid preparations

� Cheaper; “more natural”

� Primarily derived from beef & pork thyroid glands

� Do not have consistent amts of thyroid hormones

� Content & bioavailability vary from dose to dose

� Serum fluctuations more likely to cause cardiac symptoms

� Should NOT be substituted for prescription drug


Agents

� Natural

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Agents

� Synthetic

� 1. levothyroxine (T4) – Synthroid, Levoxyl

� 35% of T4 converts to T3

� Longer ½ life (6-7 days)

� 2. liothyronine (T3) - Cytomel

� 3-4x more active

� Greater risk of cardiotoxicity

� 3. liotrix - Thyrolar

� A 4:1 mixture of T4 & T3

levothyroxine (Synthroid)

� Prescribing levothyroxine for tx of hypothyroidism

� Adults:

� Initiate at 50 mcg/day

� Increase in increments of 25 mcg/day at 6 wk intervals

� Usually up to 100-150 mcg/day

� Target dose based on TSH levels & patient symptoms

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� Prescribing levothyroxine for tx of hypothyroidism

� Elderly:

� Initiate at 25 mcg/day

� Increase in increments of 12.5 -25 mcg/day at 6-8 intervals

� Target dose based on TSH levels & patient response

*** also, lower doses & longer intervals for changing doses in

patients with CVD


� Prescribing levothyroxine for tx of

hypothyroidism

� Pregnancy:

�Increasing the dose by 25-30%

usually results in adequate

coverage during pregnancy

�Check TSH in 4 weeks to

determine any dosage

adjustment

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� Prescribing levothyroxine for tx of

hypothyroidism

� Congenital Hypothyroidism:

�Tablets may be crushed and added to infant formula

�Soy-based formula may impair absorption

�Need referral to pediatric endocrinologist


� Inappropriate Uses of Thyroid Hormones:

� Obesity

�Weight loss

� Depression

� Increase energy or mood

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� Take at same time QD

� Usually morning (before breakfast)

� Prevent insomnia

� Take on an empty stomach (1/2 hr before meals or 2 hrs

after meal)

� Variably absorbed

� Fasting increases absorption

� High-fat & high-fiber decrease

absorption


� Separate from other meds by >2 hrs

� Rx, OTC, vit/minerals (may decrease absorption of

levothyroxine)

�Bile-acid sequestrants (colesevelam - WelChol)

�Iron

�Antacids (calcium, aluminum)

� Be aware of multiple drug interactions when

prescribing levothyroxine

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� Do NOT switch brands

� Not bioidentical therapeutically

� If switch brands, retitration of dose may be

needed

� Color coded: not standardized across

manufacturers


� Missed dose

� Single dose, then take that day as soon as remembered

� >3 missed doses, then inform NP

� Therapy is life-long

� Instruct patient to never stop taking it without first consulting the health care provider

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� Monitoring:

� Must achieve steady state to have reliable values

� Long ½ life (take 6 wks to achieve steady state)

� Initiate levothyroxine & check TSH level in 6 weeks


� Monitoring:

� Stable TSH may take 6-12 months to achieve

� Euthyroid goal:

� TSH goal: 0.5-5 (preferably 1-2) mU/L

� Consider clinical symptoms

� Check TSH 6 wks after any dosage adjustment

� ***infants/children checked more frequently

� Especially during growth spurts

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� Adverse Drug Reactions (ADR):

� 1. S/S hyperthyroidism

� Increased HR (check pulse – if >100 hold dose & contact NP)

� Increased BP

� Nervousness, anxiety, tremors, insomnia

� Intolerance of heat, excessive perspiration

� Weight loss despite increased appetite

� Diarrhea

� Menstrual irregularities

� Assess TSH & adjust dose accordingly

� 2. Children: may experience temporary partial hair loss


� Precautions/Contraindications

� 1. Cardiovascular disease

�CAD, recent MI

� 2. Osteoporosis

�Long-term therapy assoc with decreased bone

density in hip/spine

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Hyperthyroidism:

Antithyroid Agents

� Hyperthyroidism (thyrotoxicosis)

� Breakdown in feedback loop

� Excessive levels of thyroid hormones

� Most common cause = Graves’ disease (autoimmune)

� Severe = thyroid storm = life-threatening

� Goal of pharmacologic therapy is to either:

� 1. inhibit the synthesis of thyroid hormones

� 2. destroy thyroid gland tissue (radioactive iodine – I 131)

Hyperthyroidism

� Hyperthyroidism

� S/S = tachycardia, nervousness, anxiety, tremors, insomnia,

weight loss, heat intolerance, diarrhea

� Treatment – monitor:

� Clinically: S/S

� Lab: TSH

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Antithyroid Agents

� 3 major categories:

� 1. thioamide derivatives

� propylthiouracil (PTU)

� methimazole (Tapazole)

� 2. iodides (nonradioactive)

� Lugol’s solution

� 3. radioactive iodine

� I 131

Antithyroid Agents


� MOA: blockage of thyroid hormone synthesis (inhibits

incorporation of iodine)

� Does NOT destroy existing stores of thyroid hormones

� Once therapy is started, therapeutic effects will not occur until

existing stores are depleted

� it may take several weeks

� Used only in adults

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Antithyroid Agents


� Short ½ life (2 hours)

� TID

� Highly protein bound

� Low concentrations cross placenta or into breast milk

� Metabolized in liver with significant first-pass effect

Antithyroid Agents


� AE:

� Drowsiness, HA, vertigo, diarrhea, nausea, arthralgia, paresthesias

� Agranulocytosis (decreased WBCs)

� Rare

� Occurs first 1-2 mo of therapy

� CBC; observe for S/S infection; reversible when PTU is dc’d

� Teach patients to report: fever, chills, sore throat

� Drug-induced hepatitis BLACK BOX WARNING

� LFT (liver function tests)

� Teach patients to report: unusual HA, malaise, weakness,

yellowing of eyes/skin

� Therapy required 6-18 months

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Antithyroid Agents


� Preferentially used in almost all cases (may be used in pediatrics)

� Fewer adverse effects

� MOA: blockade of thyroid hormone synthesis (inhibits incorporation

of iodine)

� Does NOT destroy existing stores of thyroid hormones

� Several weeks to see therapeutic effects

� AE:

� Drowsiness, HA, vertigo, diarrhea, nausea, arthralgia, paresthesias

� Agranulocytosis

� Drug-induced hepatitis

� Longer ½ life: QD dosing

Antithyroid Agents


� Critical thinking…

� Lipid soluble

� Not protein bound

� Freely cross placenta and into breast milk???

� PTU preferred in pregnant women

� PTU = use in pregnancy

� methimazole = most others

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Hyperthyroidism

� Beta-Blockers

� Treat SYMPTOMS

�Tachycardia

� Ex:

�1. propranolol (Inderal)

�2. atenolol (Tenormin)

nsc 830 thyroid - eastern kentucky university · 2015-08-13 · 8/12/2015 1 nsc 830: drugs...

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