Pharma L2 Thyroid & Antithyroid Drugs Flashcards
Which drugs accelerate breakdown of thyroid hormones ?
Phenytoin, phenobarbital, rifampin
Which drugs cause primary hypothyroidism ?
Carbimazol, propyl-thyrouracil
Liothyronin (T3) & Levothyroxine (T4) PKs
1) TSH levels determine improvement
2) Levothyroxine stronger binding to plasma proteins—> long duration with slow onset
3) Drug if choice is Levothyroxine
Levothyroxine Food & drug interactions
1) Given on empty stomach (soybeans & walnuts decrease absorption)
2) 2-4 hrs before or after calcium or iron supplements (since they reduce absorption)
Enzyme inhibitors
1) Grapefruit
2) Cimetidine
3) ketoconazol
4) Erythromycin
5) ciprofloxacin
6) omeprazol
Enzyme inducers
Alcohol, phenobarbital, carbamazepine, rifampin, phenytoin
Which drugs decrease synthesis of hormones?
Thioamides: Carbimazole, propyl-thiouracil, methimazole
Thioamines MOA
1) inhibit TPO (inhibits Iodide ion oxidation to iodine)
2) inhibit Coupling
3) PTU inhibits peripheral deiodinase
Onset of Thioamines and why?
Delayed & slow because no effect on stored thyroglobulin
Which of the thioamines is teratogenic and which isn’t?
Methimazole (long HL) is teratogenic while PTU is not (Short HL highly ionized in blood)
What is the active form of carbimazole?
Methimazole
Thioamines S/E
Agranulocytosis (granulocyte deficiency), hepatotoxicity
Drug of choice in treating Hyperthyroidism ?
Methimazole
MOA of iodide (Lugol’s solution)
1) Inhibit T3 & T4 protease enzyme preventing its release from thyroglobulin
2) transient inhibition of iodination
3) reduce size and blood supply to the gland
Therapeutic use of Lugol’s solution
Not used as solo, used in thyroid storm and before surgery