A 35 years old woman came with complaints of heat intolerance, retraction of upper eyelid
and menstrual irregularities. Her T3 , T4 , FT4 & FT3 are elevated while TSH is suppressed.
Answer the following:
(a) Which drugs can be administered to reduce the thyroid activity in this patient. 2 mark(s)
(b) What is its mechanism of action. 2 mark(s)
(c) Which drug is preferred, if the patient is pregnant. 1 mark(s)
(d) What is the route of administration of I131. 1 mark(s)
Q26 marksEssays
Answer
This clinical picture (heat intolerance, lid retraction, menstrual irregularity, elevated T3/T4/FT4/FT3 with suppressed TSH) is consistent with hyperthyroidism (thyrotoxicosis).
(a) Drugs to reduce thyroid activity
Carbimazole / Methimazole
Propylthiouracil
(b) Mechanism of action
Thioamides inhibit the enzyme thyroid peroxidase, blocking iodine organification (incorporation of iodine into tyrosine residues) and coupling of iodotyrosines (MIT/DIT) to form T3/T4 — reducing new thyroid hormone synthesis
Propylthiouracil additionally inhibits peripheral conversion of T4 to the more active T3
(c) Preferred drug in pregnancy
Propylthiouracil (preferred, particularly in the first trimester — carbimazole/methimazole carry a small risk of aplasia cutis and choanal/oesophageal atresia)
