Thyroid

Question 1

Hormone Regulation

Answer 1

Bone formation- PTH: calcium, phosphorus
Growth formation- estrogens, androgens: testosterones; GHRH –> GH (Somatropin)
Metabolic rate control- TSH, thyroid hormone (TH)
BP and fluid balance control- cortisol, aldosterone, ADH

Question 2

Human Growth Hormone

Answer 2

Somatropin (genotropin)

• Recombinant DNA technology is true human factor
• Stimulates the growth and metabolism of nearly every cell in the body
• Uses: short stature with or without normal GH levels
• – Contraindicated in patients with closed epiphyses
• – Dosing is highly individualized on the basis of child’s growth rate and anticipated trajectory of genetic height

Question 3

Human Growth Hormone: Pharmacodynamics

Answer 3

• Initially there is insulin-like effect
• Stimulates growth of linear bones, skeletal muscles, and organs
• Stimulates erythropoietin

Question 4

Human Growth Hormone: Pharmacokinetics & ADRs

Answer 4

Pharmacokinetics: IM & SC drugs well-absorbed

• Metabolism: hepatic, renal 90%
• Excretion: renal

ADRs:

• Antibody development
• hyperglycemia, edema
• hypothyroidism
• arthralgia, HA, dizziness, flu-like symptoms

Question 5

Human Growth Hormone: Patient Education & Rational Drug Selection

Answer 5

Patient Education

• Pediatric administration: total weekly dose (0.16 to 0.24 mg/kg) divided in 6-7 doses
• ADRs
• Lifestyle management and need to prevent abuse

Rational Drug Selection: Not initiated by NP in primary care practice; work with endocrinologist

Question 6

Human Growth Hormone: Monitoring

Answer 6

• Hepatic/renal function: before and during treatment

- TSH, glucose, glycohemoglobin, based on symptoms and prior illnesses

Question 7

Thyroid Hormones: Pharmacodynamics

Answer 7

Levothyroxine (T4), Liothyronine (T3), and Liotrix (a 4:1 mixture of T4 & T3)

• There hormones produce the same effects in the body as endogenous thyroid hormones
• They also produce a negative feedback loop to reduce further secretion of TSH and thyroid hormones
• T4 is the drug of choice for thyroid replacement and suppression therapy because of its longer half-life

Question 8

Thyroid Hormone: Pharmacokinetics

Answer 8

Absorption: oral- erratic 40-80%; decreased by age, food, health of GI tract; greater than 99% is protein bound

Metabolism: liver, T4 is converted to T3 in the body; T4 produces both hormones

Excreted: bile/feces

Question 9

Thyroid Hormone: Precautions & Contraindications

Answer 9

Contraindicated after acute MI or thyrotoxicosis
Pregnancy risk factor A, and safe with children
- replacement is advised for all pregnant women
- increased metabolic rate during pregnancy may require higher dosing from baseline
- thyroid hormones are minimally excreted in breast milk
- Children with hypothyroidism need treatment

Question 10

Thyroid Hormone: ADRs

Answer 10

Symptoms of hyperthyroidism:

• CV: angina, increased BP, flushing, palpitations
• Central nervous system: anxiety, HA, insomnia

Long-term thyroid replacement associated with decreased bone density in hip/spine in postmenopausal women

Question 11

Thyroid Hormone: Drug Interactions

Answer 11

Bile-acid sequestrants, iron salts, and antacids decrease absorption; estrogens may decrease response

Drugs may decrease action of warfarin, digoxin, and beta blockers

Question 12

Hypothyroidism: Clinical Treatment

Answer 12

Treatment is indicated in patients with TSH levels greater than 10 or in patients with TSH levels between 5 and 10 in conjunction with goiter or positive antithyroid peroxidase antibodies (or both)

Thyroxine replacement is typically lifelong

Consult with pediatric endocrinologist before treating a pediatric patient

Question 13

T4 Dosing: For patients with no known CV disease

Answer 13

• Initial dose can be started at 50 mcg/day for 2 to 4 weeks and may be increased in increments of 25 mcg/day
• Average full replacement 100-124 mcg/day

Question 14

T4 Dosing: For patients 50+ years with CV disease or with long-standing hypothyroidism

Answer 14

• Initial dosing of T4 is 12.5 to 25 mcg/day
• An increase of 12.5 to 25 mcg increments at approximately 1 month intervals avoids rapid increases in cardiac workload and symptoms of ischemic heart disease
• If exacerbations of angina pectoris occurs, the previous dosage regimen should be administered and titrated up in smaller increments

Question 15

T4: Rational Drug Selection

Answer 15

T4 is drug of choice for thyroid replacement and suppression therapy

In older adults with no cardiac disease, consider consulting with endocrinologist regarding using T3 or T4 or liotrix

Question 16

Thyroid Agents: Monitoring

Answer 16

• TSH level should be measured in 6-8 weeks, and the T4 dose should be adjusted as necessary
• The target TSH level should be between 0.3 and 3.0
• Once a stable TSH level is achieved, annual examination is appropriate
• Monitor for osteoporosis in high-risk populations
• Many drugs affect TSH levels

Question 17

T4: Patient Education

Answer 17

• Take medication each day in the morning, preferably before breakfast because absorption is increased on an empty stomach
• ADRs: Learn how to measure heart rate
• Lifestyle management is important

Question 18

Antithyroid Agents: Pharmacodynamics

Answer 18

Propylthiouracil (PTU), methimazole (Tapazole)

• Both block synthesis of T4 and T3
• Neither drug treats the underlying pathology in hyperthyroidism
• High relapse rates exist but are less likely if treated for 18-24 months

Question 19

Antithyroid Agents: Pharmacokinetics

Answer 19

Absorption: rapidly absorbed after oral dosing, peaking within 1 hours: 85% to 95% bioavailability

PTU is 75% to 80% protein bound; methimazole is NOT protein bound

Both metabolized in the liver; both have short half-life; excreted in urine: 35% of PTU, 80% of methimazole

Question 20

Antithyroid Agents: Precautions, Contraindications, ADRs, & Drug Reaction

Answer 20

Precautions & Contraindications

• Pregnancy major concern: readily cross the placenta
• – Recommend that patient not get pregnant while on these drugs
• High concentrations in breast milk
• PTU not recommended in children

ADRs: agranulocytosis, drowsiness, HA, alopecia, skin rashes, renal/hepatic failure
Drug Reaction: lithium, warfarin

Question 21

Antithyroid Agents: Rational Drug Selection & Monitoring

Answer 21

Rational Drug Selection
- Check guidelines, as use in pregnancy and children varies frequently

Monitoring

• Thyroid studies, CBC, liver/renal panels before starting drug
• Recheck in 1-2 months after starting drug

Question 22

Antithyroid Agents: Patient Education

Answer 22

• Administration: very important to NOT miss doses; if dose is missed, patient should NOT make up dose
• Teach about hypothyroid symptoms; prolonged subclinical hyperthyroidism is associated with bone loss, a. fib., and impaired left ventricular diastolic filling
• Dietary sources of iodine should be reduced because they interfere with action of drugs
• Watch use of OTC cold medicines

Question 23

Posthyperthyroid Treatment

Answer 23

Patients need to expect that they will become hypothyroid

This may not occur for several months

Patients must take thyroid supplements for life