Thyroid Disorders Flashcards
Medications used in hyperthyroidism
Propylthiouracil
(Reserved for patients intolerant to carbimazole)
Carbimazole
They both work by interfering with the synthesis of thyroid hormones
What is the use of beta blockers in relieving of thyrotoxic symptoms
Propanolol/nadolol for rapid relief of symptom together with antithyroid drugs or radioactive iodine
Used in neonatal thyrotoxicosis and supraventricular arrhythmias due to hyperthyroidism
Lab result of thyroid function are not altered by beta blockers
Treatment of thyrotoxic crisis
IV of fluids Propanolol Hydrocortisone Iodine solution Carbimazole/propylthiouracil (through nasogastric tube)
Pregnancy and hyperthyroidism
Radioactive iodine therapy contraindicated
Blocking-replacement regimen is not suitable
Propylthiouracil remains the drug of choice for 1st trimester and carbimazole for 2nd trimester because of risk of hepatotoxicity with with the propylthiouracil
Both cross the placenta and high doses can cause fetal goitre and hypothesis
Presenting in milk affecting neonatal thyroid function so monitor neonatal development
Carbimazole indications
Hyperthyroidism
15-40 mg daily and continue until patient becomes euthyroid usually takes 4-8 weeks
Blocking-replacement therapy in combo with levothyroxine
40-60mg daily for 18months
Blocking replacement regimen
Used in graves hyperthyroidism to completely block the synthesis of thyroid hormone while replacing thyroid hormone
Dose equivalence of carbimazole and propylthiouracil
1mg of carbimazole equals 10mg propylthiouracil but dose may need adjustment according to response
Carbimazole side effects
Arthralgia
Gastro-Intestinal disturbances
Taste disturbance
Fever/malaise/sore throat/bruising/ mouth ulcers report because associated with bone marrow suppression
Rash and pruritus common and treated with antihistamines or switch to propylthiouracil
Propylthiouracil dosing
Initially 200-400mg daily in divided doses until euthyroid then reduce to 50-150mg daily in divided doses
Similar side effects to carbimazole
Reduce dose in hepatic impairment because hepatotoxic —monitor!
And reduced dose in renal impairment
Hypothyroidism and hashimoto’s thyroiditis (chronic lymphocytic thyroiditis) treatment
Levothyroxine
Liothyronine (more rapidly metabolised and more rapid effect)
Levothyroxine doses
18-64 years old: initiate with 50-100mg micro/day, adjust in steps of 25-50micro every 3-4 weeks
Maintenance: 100-200micro
Over 65 years old: initiate with 25micro/day, adjust in steps of 25micro every 4 weeks
Maintenance: 50-200micro
Blocking replacement therapy: 50-150micro for 18months
Hypothyroidism with cardiac disease: like over 65 years old
Levothyroxine cautions and contraindications
Contra: thyrotoxicosis
Cautions: CV disorders, diabetes insipidus/mellitus (dose of antidiabetic or insulin might need to increase), elderly, hypertension
Initiate corticosteroid therapy before starting levothyroxine
Monitoring/cautions with levothyroxine
CV disorders
➡️baseline ECG because changes induced by hypothyroidism can be confused with ischeamia
Initial dosage: if metabolism increases too rapidly(=diarrhoea,nervousness, rapid pulse, insomnia, tremors and angina pain)
➡️reduce dose or withhold for1-2 days and start at lower dose
Pregnancy
➡️levothyroxine requirements increase during pregnancy
Liothyronine dosing
10-20micro daily increased by 60micro daily in 2-3 divided doses
20-25micro equivalent to 100 levothyroxine
Any change in brand should be monitored cause non bio equivalent if not licensed brand in uk
Thyroid hormone interactions
Calcium salts: decrease absorption of levothyroxine
Ferrous fumarate: decreases absorption of levothyroxine (at least 2 hours apart)
Anti epileptics (phenytoin/phenobarbital/ carbamazepine) increase risk of hypothyroidism
Amiodarone: increase risk of thyroid dysfunction
Anticoagulants (coumarins): enhances anticoagulant effect
