Module 3: Thyroid and Adrenal Disorders Flashcards
Thyroid Hormone Production
Pathway:
- Hypothalamus secretes TRH
- TRH stimulates anterior pituitary to secrete TSH
- TSH stimulates the thyroid gland to produce thyroid hormones T3 and T4
- Biologic effects
Thyroid hormones three main actions:
- Stimulate energy use
- Stimulate the heart
- Promote growth and development
T4 elevation inhibits the secretion of TSH (feedback loop)
Thyroid Disorder: Hypothyroidism
S/S (Decreased metabolism):
- Face is pale, puffy, and expressionless
- Skin is cold & dry
- HR and temp. lowered
- Goiter may be present
- Altered MS
- Lethargy/fatigue
Laboratory values:
- TSH elevated
- Total T4, free T4 lowered
Tx: Thyroid replacement therapy (i.e. synthetic T3 or T4)
Thyroid Disorder: Hyperthyroidism
S/S (Increased metabolism):
- Skin warm & moist
- Increased appetite
- Rapid/strong heartbeat
- Anxiety
- Skin warm & moist
- Exophthalmos (protrusion of the eyeballs) — wrt antibodies (Grave’s)
Laboratory values:
- TSH lowered
- Total T4, free T4 elevated
Tx: Thyroid removal, radioactive iodine (destroys tissue to stop over-production of thyroid hormones), and antithyroid meds.
Thyroid Hormone Preparations
Prototype: Levothyroxine
MOA: Synthetic form of T4 that mimics T4 functions
Therapeutic use: All forms of hypothyroidism (usually Hashimoto’s autoimmune disorder)
Dosage form:
- IV dose 50% lower than oral dose — used for severe, life-threatening hypothyroidism (myxedema coma)
- Oral — FDA allows interchangeability, but AACE does not (due to discrepancy of bioequivalence)
PK: Half-life = 7 days
DDIs:
- Drugs that reduce levothyroxine absorption — i.e. vitamin supplements, acid suppressors
- Drugs that increase levothyroxine metabolism (strong inducers) — i.e. phenytoin, carbamazepine, rifampin
- Warfarin simultaneously depletes vitamin K dependent clotting factors
AEs (Narrow therapeutic index dosing that is very pt-sepcific, overall well tolerated, and requires monitoring):
- Thyroid storm
- Atrial fibrillation
- Bone loss
RN implications:
- Assess pt for S/S of hypothyroidism, and thyroid storm (tachycardia, angina, tremor, nervousness, insomnia, hyperthermia, heat tolerance, sweating)
- Monitor pt’s T4 and TSH levels for effectiveness
Pt education:
- Admin. meds. on empty stomach (at least 30-60 min. before breakfast)
- Consult with pharmacist or provider before switching levothyroxine preparation — potential for a varied response from different products
- Continue for life, even if feeling better
- Warn pts about DDI risk, especially absorption
Anti-Thyroid Drugs
Prototype: Methimazole
MOA:
- Suppresses synthesis of thyroid hormone
- Prevents oxidation of iodine and from being incorporated into tyrosine, but does not destroy thyroid hormone stores
PK: Half-life = 6-13 hours; takes 3-12 weeks to reach euthyroid state
Therapeutic use:
- Hyperthyroidism (generally Grave’s)
- Thyrotoxic crisis (thyroid storm)
Individual variation:
- Pregnancy — fetus in first trimester does not produce thyroid
- Pt at risk for liver failure
- Immunosuppression — can cause agranulocytosis
AEs (Generally well tolerated):
- Agranulocytosis: dramatic reduction in circulating granulocytes (increased risk of infection) — Early S/S: Sore throat, fatigue, and fever (within 2 mos. of therapy)
- Hypothyroidism
RN implications:
- Admin.: follow hazardous precautions (some teratogenic effects)
- Monitor: S/S of hypo/hyperglycemia and agranulocytosis; TSH levels and WBC counts (at baseline and periodically)
Pt education:
- Take med. at the same time daily
- Refrain from abrupt discontinuation
- Maintain consistent diet and notify physician of any diet changes that increase consumption of iodine-containing foods (i.e. seafood, salt-containing products)
- Be aware of S/S of hypothyroidism and agranulocytosis
Adrenal Hormones
Glucocorticoids:
- Promote glucose availability
- Promote fat and protein breakdown
- Maintains the vascular system
- Promote CNS excitability
- Support muscle function
- Respiration function in neonates
Mineralocorticoids:
- Promote sodium and potassium balance (RAAS)
- Maintains the CV homeostasis
HPA Axis:
Pathway:
- Circadian rhythms and stress
- Stimulates the hypothalamus to release CRH
- CRH stimulates the anterior pituitary to release ACTH
- ACTH stimulates the adrenal cortex to release cortisol
- Biologic effects
Functions:
- Stress response
- Regulates glucose release and metabolism
- Fluid and electrolyte balance
Adrenal Disorder: Addison’s Disease
S/S (Adrenal insufficiency):
- Anorexia, N/V, weight loss
- Hypotension
- Electrolyte imbalances
Tx: Physiologic replacement with meds. (lifelong) — physiologic vs. stress dosing
Adrenal Disorder: Cushing’s Syndrome
S/S (Glucocorticoid excess):
- Hyperglycemia
- HTN
- Fat redistribution
Tx:
- Surgical removal followed by physiologic replacement
- Little to no role of drug therapy
Glucocorticoids
Prototype: Hydrocortisone (-sone, -solone)
MOA: Mimics effect of natural steroid hormone
Therapeutic use:
- Acute and chronic replacement therapy for adrenal insufficiency (physiologic dose)
- Non-endocrine disorders (lower dose) — i.e. CA, inflammation, and allergic reactions (pharmacologic doses)
Dosage forms:
- IV — extreme stressors, trauma (i.e. surgery)
- PO (lifelong)
AEs (Overall well tolerated):
- Adrenal suppression
- GI discomfort
- Infection
- Cushing’s syndrome
- Osteoporosis
RN implications:
- Monitor pt’s baseline electrolytes, weight, and HR
- Monitor for S/S of infection
- Monitor pt’s stool and signs of GI discomfort (bloody or tarry stools, abdominal pain, or blood-tinged emesis)
Pt education:
- Pt to follow prescribed dosing schedule
- Do not stop abruptly
- Lifelong therapy
- Warn pt’s that dose may increase at times of stress
Emergency preparedness:
- Dosage may be increased at times of stress
- For mild or febrile illness, follow the “3 times usual dose x 3 days” rule
- Advise pt to carry an emergency supply of oral and IV products at all times
- Wear medic alert bracelet
Acute Adrenal Insufficiency: Adrenal Crisis
S/S:
- Hypotension
- Dehydration
- Weakness
- Lethargy
- GI symptoms
Triggered by adrenal failure, pituitary failure, failure to receive adequate replacement during stress, and/or abrupt discontinuation of high dose glucocorticoid therapy
Tx:
- IV hydrocortisone as IV bolus followed by IV NS with dextrose
- Additional IV hydrocortisone admin. q8h
Mineralocorticoid
Prototype: Fludrocortisone
MOA: Mimics effect of natural steroid hormones
Therapeutic use: Acute and chronic replacement therapy for adrenocortical insufficiency (with glucocorticoid)
AEs (Overall well tolerated):
- HTN
- Edema
- HF
- Hypokalemia
- Cardiac enlargement
RN implications:
- Monitor pts for excessive weight gain
- Educate pt’s on manifestations of sodium and water retention
- Monitor breath sounds, BP, and serum potassium