Thyroid Flashcards
Hormone Regulation
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
Human Growth Hormone
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
Human Growth Hormone: Pharmacodynamics
- Initially there is insulin-like effect
- Stimulates growth of linear bones, skeletal muscles, and organs
- Stimulates erythropoietin
Human Growth Hormone: Pharmacokinetics & ADRs
Pharmacokinetics: IM & SC drugs well-absorbed
- Metabolism: hepatic, renal 90%
- Excretion: renal
ADRs:
- Antibody development
- hyperglycemia, edema
- hypothyroidism
- arthralgia, HA, dizziness, flu-like symptoms
Human Growth Hormone: Patient Education & Rational Drug Selection
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
Human Growth Hormone: Monitoring
- Hepatic/renal function: before and during treatment
- TSH, glucose, glycohemoglobin, based on symptoms and prior illnesses
Thyroid Hormones: Pharmacodynamics
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
Thyroid Hormone: Pharmacokinetics
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
Thyroid Hormone: Precautions & Contraindications
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
Thyroid Hormone: ADRs
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
Thyroid Hormone: Drug Interactions
Bile-acid sequestrants, iron salts, and antacids decrease absorption; estrogens may decrease response
Drugs may decrease action of warfarin, digoxin, and beta blockers
Hypothyroidism: Clinical Treatment
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
T4 Dosing: For patients with no known CV disease
- 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
T4 Dosing: For patients 50+ years with CV disease or with long-standing hypothyroidism
- 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
T4: Rational Drug Selection
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
Thyroid Agents: Monitoring
- 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
T4: Patient Education
- 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
Antithyroid Agents: Pharmacodynamics
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
Antithyroid Agents: Pharmacokinetics
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
Antithyroid Agents: Precautions, Contraindications, ADRs, & Drug Reaction
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
Antithyroid Agents: Rational Drug Selection & Monitoring
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
Antithyroid Agents: Patient Education
- 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
Posthyperthyroid Treatment
Patients need to expect that they will become hypothyroid
This may not occur for several months
Patients must take thyroid supplements for life
