Thyroid PHARM Flashcards
Levothyroxine
MOA
Synthetic T4
Tetra-iodothyronine
Converted in periphery to T3
Tri-iodothyronine
biologically active
transcription factor
transcription of genes involved in
- BMR
- Heart
- Growth & Development
Levothyroxine
Half life and patient monitoring
Half life is 7 days
It takes 28 days (approximately 4-6 weeks) to reach therapeutic effect
Patient monitoring
4-6 week mark
annually
Levothyroxine
SE
Thyrotoxicosis if level is too high
Cardio:
tachycardia, racing heart
tachydysrhythmias, palpitations
increase metabolic demand of heart
angina pain
BMR:
hyperthermia (heat intolerance)
diaphoresis
hyperglycemia
Accelerated bone loss
Weight loss
CNS:
nervousness
anxiety
tremor
racing thoughts
insomnia
*More common in elderly
Hypothyroidism if level is too low
Levothyroxine
AE
Thyrotoxicosis
Heart: dysrhythmias, tachycardia, angina, ischemia
BMR: bone, muscle, glycogen reabsorption
Levothyroxine
Drug interactions
Drugs decrease absorption:
antacids
H2 antagonists
PPIs
sucrafalate
bile acid sequestrates
Drugs that increase metabolism:
AED
SSRIs
Antagonistic to these drugs:
Digoxin
Beta blockers
insulin and hypoglycaemic agents
PRN prescriptions
accompany levothyroxine
Vitamin D3
Calcium
Levothyroxine and pregnancy
Increase BMR during pregnancy
Requires increase dosage in first trimester
Baby does not produce thyroid hormone and dependent for normal growth and development
Dosage plateaus in second and third trimester
Levothyroxine and neonatal hypothyroidism
Requires thyroid hormone for normal growth and development
within 4 weeks to prevent irreversible growth, development, and CNS effects
Patient Education
Levotyroxine
Brands are not interchangable
Change of dose requires monitoring blood 4-6 weeks
TSH monitoring
Take on empty stomach, 1 hour before eating
Therapy is life long and required for survival
Report S&S dosage is too high: palpitations, chest pain, tremor, nervousness, insomnia, sweating, heat intolerance
Take calcium and vitamin D
Levothyroxine
Patient monitoring
Monitor every 6-8 weeks until TSH normalizes and then annually
Serum: TSH, T4
Children: monitor height (normal growth, development)
Symptoms: hyper or hypothyroidism
Indications
Levothyroxine
Hypothyroidism
Congenital hypothyroidism (neonate)
Myexedema coma
Examples
Synthetic Thyroid Hormone
T4: levothyroxine
T3: Liothyronine
T3/T4: Liotrix (mixture)
Methiomazole (MMI)
MOA
- Blocks peroxidase enzyme in the thyroid follicular cell: prevents oxidation of iodide to iodine (cannot be added to tyrosine)
- Blocks coupling of iodinated tyrosines (blocks synthesis of T3 and T4)
*3-12 weeks to take effect
Thyroid colloid cells have T3 and T4 stores
Indication and Duration of therapy
Methimazole (MMI)
Hyperthyroidism
First line therapy
Grave’s Disease
Pre-surgical prophylaxis: prevent thyroid storm
Thyrotoxicosis
Duration: 1-2 years
Methimazole
Special populations and contraindications
- Pregnancy and breast feeding
- not to be taken in first trimester
- caution breast feeding
- neonatal hypothyroidism and goitres - Liver disease
- AE: hepatitis and liver failure - Blood dyscrasia
- AE: agranulocytosis
Methimazole
SE
Hypothyroidism
- dosage too high
- monitor S&S: brittle hair, nails, cold, fatigue, lethargy, weight gain, depression, mental slowing
Liver disease
- hepatitis and liver failure
- S&S: anorexia, n/v, dark urine, jaundice, RUQ pain
Agranulocytosis
- Requires D/C and treatment with PRN filgastrim
- S&S: infection, fever, sore throat
Patient Education
Methiomazole
Women child bearing age
- teratogenic first trimester
- contraception and child planning
Monitor S&S liver disease
Monitor S&S infection
Monitor S&S hypothyroidism
Blood Monitoring
Methimazole
Baseline:
CBC (SE: agranulocytosis)
LFTs (SE: liver disease)
TSH, T3, T4 (dosing)
HCG (SE: teratogenic first trimester)
Follow up:
CBC
LFTs
S&S hypothyroidism
Methimazole
Pregnancy and Breastfeeding
Free
Crosses placenta
Not safe in first trimester
*does not enter breast milk
Propylthiouracil (PTU)
MOA
Blocks the conversion of T4 (tetraiodothyronine) to T3 (triiodothyronine) in the periphery
T3 is the bioactive thyroid hormone
Propylthiouracile (PTU)
Indications
Second line therapy
Hyperthyroidism
Pregnancy
First line therapy , first trimester
Thyroid Storm
First line therapy - direct action, prevent conversion to bioactive form
Propylthiouracil (PTU)
AE
Liver failure without warning
much more common and severe
*used in the first trimester of pregnancy (does not cross placenta or into breast milk)
Propylthiouracil (PTU)
SE
Hypothyroidism:
Lethargy, low BMR, low HR, low BP, cold intolerance, weight gain, brittle hair and nails, etc.
Liver failure
Patient education
Propylthiouracil (PTU)
Monitor S&S liver disease; anorexia, nausea, vomiting, fullness, abdominal pain, jaundice, dark urine, pale stools
Monitor S&S hypothyroidism: low HR, BP, fatigue, lethargy, depression, cold intolerance
Radioactive Iodine (I-131)
Indication
Hyperthyroidism
Failure thionamides
Failure surgical resection
Prophylaxis surgical resection
Thyroid storm
Radioactive Iodine (I-131)
Contraindications
Pregnancy
Breastfeeding
Children
- lifelong thyroid therapy
Radioactive Iodine I-131
MOA
Taken up by thyroid follicular cells
radioactive iodine decays
beta particles (harmful) damage follicular cells
gamma particles (harmless)
Radioactive Iodine I-131
SE/AE
- Delayed hypothyroidism
life long thyroid hormone dependence
more common children
*contraindication pregnancy, breastfeeding - Effects take weeks or months
- require thionamide therapy while waiting - Iodism
- GI corrosion, perforation, bleeds
- bleeding gums
- brassy taste
Thyroidectomy
Indications
Hyperthyroidism
Thyroid carcinoma
Goitres
Thyroidectomy
Complications
Infection
Hypothyroidism
Hypoparathyroidism
Damage to laryngeal nerve
Thyroid storm
Non-Radioactive Iodine (Lugol)
MOA
High concentration of iodine inhibits thyroid gland
- decreases iodine uptake
- decrease T3, T4 synthesis (iodination, coupling, release)
Non-Radioactive Iodine (Lugol)
Indications
Prophylaxis pre-surgery to prevent thyroid storm
Thyroid storm
10ggt Q8 hours
*tolerance develops with long term use
Peak 10-15 days
Pregnancy
Hyperthyroidism treatments
Contraindicated
- Methimazole first trimester (neonatal hypothyroidism, goitre)
- radioactive iodine
Approved
- propylthiouracil (PTU) first trimester
- MMI second and third trimester
Pregnancy
Hypothyroidism treatment
All women screened in first trimester for hypothyroidism
- congenital growth, development, CNS defects
Increase thyroid hormone demands in first trimester by 30-50%
- baby doesn’t make thyroid hormone until 2nd and 3rd trimester
Increased monitoring
- dosage plateau in 2nd and 3rd trimester
Paediatrics
Hyperthyroidism treatment
Contraindicated
- radioactive iodine - thyroid hormone dependence
- propylthiouracil - liver failure
Approved
- surgery
- MMI weight based dosing
Paediatric hypothyroidism
Treat right away
prevents growth, development, CNS (learning, memory, IQ)
must be treated within 4 week window of being born to prevent permanent deficits
