Anti-thyroid Drugs

Anti-thyroid Drugs

Q. 1

Which can be used in pregnancy ‑

 A >ACE inhibitors
 B >Aldosterone
 C >AT receptor antagonist
 D >Propylthiouracil
Q. 1

Which can be used in pregnancy ‑

 A >ACE inhibitors
 B >Aldosterone
 C >AT receptor antagonist
 D >Propylthiouracil
Ans. D

Explanation:

Propylthiouracil [Ref: K.D.T. 6/e. 251, 484, 488; Progress in obs & Gynae 18/e p. 52, 53, 54 (Studds)]

  • Propylthiouracil is the drug of choice for hyperthyroidism during pregnancy.

Antithyroid drugs in pregnancy

  • Propylthiouracil and methirnezole are both antithyroid drugs that cross the placenta and can lead to fetal goiter.
  • Methimazole has been associated with “cutis aplasia”.
  • Scalp defects cloanal atresia esophageal atresia and increased maternal side effects.
  • Because both medications are equally effective the drug of choice for hyperthyroidism in pregnancy is propylthiouracil.
  • Propylthiouracil is not available throughout the world and in those conditions methimazole may be substituted. Antihypertensives in pregnancy
  • Angiotensin converting enzyme inhibitor (ACE inhibitor) e.g., Enalapril, captopril can cause fetal renal tubular dysplasia in the second and third trimesters leading to oligohydramenios fetal limb contractures, craniofacial deformities and hypoplastic lung development.
  • A recent large cohort study found an increased risk of congenital malformations with isolated first trimester exposure to ACE inhibitors.
  • Infants exposed in utero to ACE inhibitors were at increased risk of cardiovascular and CNS malformations.
  • Angiotensin II receptor antagonists have been shown to have second and third trimester findings consistent with  ACE inhibitors and are not recommended in pregnancy.

Aldosterone

  • We have not got any literature on the use of Aldosterone during pregnancy.
  • We are not sure of it use during pregnancy.

Q. 2

A 47-year-old woman presents with complaints of nervousness and increased sensitivity to hot weather. She is diagnosed with hyperthyroidism and prescribed propylthiouracil. What is the principal mechanism by which this drug acts?

 A

Decreasing the efficacy of TSH binding to the thyroid TSH receptor

 B

Decreasing the rate of proteolysis of thyroglobulin

 C

Increasing the amount of 3,3′,5′-triiodothyronine (reverse T3; rT3)

 D

Inhibiting deiodination of thyroxine (T4)

Q. 2

A 47-year-old woman presents with complaints of nervousness and increased sensitivity to hot weather. She is diagnosed with hyperthyroidism and prescribed propylthiouracil. What is the principal mechanism by which this drug acts?

 A

Decreasing the efficacy of TSH binding to the thyroid TSH receptor

 B

Decreasing the rate of proteolysis of thyroglobulin

 C

Increasing the amount of 3,3′,5′-triiodothyronine (reverse T3; rT3)

 D

Inhibiting deiodination of thyroxine (T4)

Ans. D

Explanation:

Propylthiouracil works primarily by inhibiting the peripheral conversion of T4 to T3.

The thyroid extracts iodide from the plasma and, in an oxidative process, iodinated tyrosine residues in thyroglobulin molecules. Monoiodotyrosine and diiodotyrosine are formed and then coupled to produce either thyroxine (tetraiodothyronine, T4) or triiodothyronine (T3).

Proteolytic cleavage of thyroglobulin molecules leads to free T3 or T4, which is then released into the circulation; T3 is several times more potent than T4. Peripheral deiodination of T4 at the 5′ position leads to T3 formation (mainly in the liver); this step is inhibited by propylthiouracil.

Decreasing the efficacy of TSH binding, decreasing the rate of thyroglobulin proteolysis, increasing the amount of rT3 formation, and inhibiting the uptake of iodide into the thyroid, would all tend to decrease the formation of thyroid hormones in the thyroid itself.

Q. 3

Which of the following drug is not teratogenic?

 A

ACE inhibitors

 B

Aldosterone

 C

AT receptor antagonist

 D

Propylthiouracil

Q. 3

Which of the following drug is not teratogenic?

 A

ACE inhibitors

 B

Aldosterone

 C

AT receptor antagonist

 D

Propylthiouracil

Ans. D

Explanation:

Propylthiouracil is the drug of choice for hyperthyroidism during pregnancy. Carbimazole when used during pregnancy results in aplasia cutis of the neonate.

ACEI and ARBs when given during later half of pregnancy results in fetal growth retardation, hypoplasia of organs and fetal death. So it is contraindicated in pregnancy.


Q. 4

Antithyroid drug of choice in pregnancy is :

 A

Propyithiouracil

 B

Carbimazole

 C

Propranolol

 D

Lugol’s iodine

Q. 4

Antithyroid drug of choice in pregnancy is :

 A

Propyithiouracil

 B

Carbimazole

 C

Propranolol

 D

Lugol’s iodine

Ans. A

Explanation:

Ans. is a i.e. Propylthiouracil

Management of Hyperthyroidism during Pregnancy :

  • Medical management is the management of choice.°
  • Antithyroid drug of choice is propylthiouracil° because it :

—    Inhibits conversion of T, to -13°

—    Crosses placenta less rapidly than rnethimazole°

—    It is not associated with aplasia cutis seen with methimazole °

  • Both propylthiouracil and methimazole / carbimazole are however effective and safe°
  • Side effect of propyithiouracil : Transient leukopenia, Agranulocytosis and Fetal hypothyroidism
  • Side effect of methimazole/carbimazole : — Aplasia cutis

—    Esophageal atresia

—    Choanal atresia

  • Radio active iodine is an absolute contraindication in the treatment of thyrotoxicosis in pregnancy. Infect it should not be given to patients even wanting pregnancy within 1 year.

Surgical Management :

  • Thyroidectomy may be carried out after thyrotoxicosis has been brought under medical control.° Because of increased vascularity of thyroid gland during pregnancy, such surgery is more complicated than in non preg‑

nant state.

  • It is indicated in women who cannot adhere to medical treatment or in whom drug therapy proves toxic.

Q. 5

Drug of choice in thyrotoxicosis in pregnancy is :

 A

Carbimazole

 B

Lugol’s iodine

 C

Propranolol

 D

Radioactive iodine

Q. 5

Drug of choice in thyrotoxicosis in pregnancy is :

 A

Carbimazole

 B

Lugol’s iodine

 C

Propranolol

 D

Radioactive iodine

Ans. A

Explanation:

Carbimazole


Q. 6

Which of the following is true of propylthiouracil‑

 A

It is used in the treatment of myxedema

 B

It has a long half-life in the circulation

 C

It increases proteolysis of thyroglobulin

 D

It blocks thyroxine synthesis

Q. 6

Which of the following is true of propylthiouracil‑

 A

It is used in the treatment of myxedema

 B

It has a long half-life in the circulation

 C

It increases proteolysis of thyroglobulin

 D

It blocks thyroxine synthesis

Ans. D

Explanation:

Ans. is ‘d’ i.e., It blocks thyroxine synthesis

o Propylthiouracil blocks thyroxine synthesis by inhibiting thyroid peroxidase, and preventing oxidation of iodide/ iodotyrosyl residues, there by

  1. Inhibit iodination of tyrosine residue in thyroglobulin.
  2. Inhibit coupling of MIT and DIT to form T3 & T4.

o Propylthiouracil also inhibit the peripheral conversion of T4 to T3.

About other options

o It is a hypothyroid drug, cannot be used in myxedema (hypothyroidism).

  • It has a short VA – 1-2 hours.
  • It does not increase proteolysis of thyroxine.

Q. 7

Methimazole differ from propylthiouracil in all except-

 A

Is secreated into milk

 B

Has more volume of distribution

 C

More protein bound

 D

All

Q. 7

Methimazole differ from propylthiouracil in all except-

 A

Is secreated into milk

 B

Has more volume of distribution

 C

More protein bound

 D

All

Ans. C

Explanation:

Ans. is ‘c’ i.e., More protein bound


Q. 8

Plasma half life of carbimazole –

 A

4 hours

 B

8 hours

 C

16 hours

 D

24 hours

Q. 8

Plasma half life of carbimazole –

 A

4 hours

 B

8 hours

 C

16 hours

 D

24 hours

Ans. B

Explanation:

Ans. is ‘b’ i.e., 8 hours

o Half life of propylthiouracil : 1-2 hours o Half life of carbimazole : 6-10 hours


Q. 9

All of following inhibit peripheral conversion of T4 and T3 except –

 A

Propylthiouracil 

 B

Methimazole

 C

Proparanolal

 D

Amiodarone

Q. 9

All of following inhibit peripheral conversion of T4 and T3 except –

 A

Propylthiouracil 

 B

Methimazole

 C

Proparanolal

 D

Amiodarone

Ans. B

Explanation:

Ans is ‘b’ i.e. Methimazole

o Propylthiouracil, propranolal, amiodarone and glucocorticoids inhibit peripheral conversion of T4 and T3.

 


Q. 10

Drug which inhibits conversion of T4 to T3 is –

 A

Carbimazole

 B

Methimazole

 C

Propylthiouracil

 D

Lugol’s iodine

Q. 10

Drug which inhibits conversion of T4 to T3 is –

 A

Carbimazole

 B

Methimazole

 C

Propylthiouracil

 D

Lugol’s iodine

Ans. C

Explanation:

Ans. is ‘c’ i.e., Propylthiouracil


Q. 11

Drug of choice for thyroid storm is:       

March 2008

 A

Thiocayanates

 B

Perchlorates

 C

Propylthiouracil

 D

Radioactive iodine

Q. 11

Drug of choice for thyroid storm is:       

March 2008

 A

Thiocayanates

 B

Perchlorates

 C

Propylthiouracil

 D

Radioactive iodine

Ans. C

Explanation:

Ans. C: Propylthiouracil

Propylthiouracil is used in thyroid storm for its inhibitory action on peripheral conversion of T4 to more active T3. It is also used in patients developing adverse effects with carbimazole.


Q. 12

Which of the following is not true regarding carbimazole:      

September 2010

 A

Safely used in pregnancy

 B

More potent than propylthiouracil

 C

Single daily dose administration

 D

Does not inhibit peripheral conversion of T-4 to T-3

Q. 12

Which of the following is not true regarding carbimazole:      

September 2010

 A

Safely used in pregnancy

 B

More potent than propylthiouracil

 C

Single daily dose administration

 D

Does not inhibit peripheral conversion of T-4 to T-3

Ans. A

Explanation:

Ans. A: Safely used in pregnancy


Q. 13

Female on carbimazole therapy presents with sudden fever, rigors and sore throat. Which is the investigation of choice for this patient?

 A

Check blood counts

 B

Check C reactive protein

 C

Take throat Swab

 D

Treat for malaria

Q. 13

Female on carbimazole therapy presents with sudden fever, rigors and sore throat. Which is the investigation of choice for this patient?

 A

Check blood counts

 B

Check C reactive protein

 C

Take throat Swab

 D

Treat for malaria

Ans. A

Explanation:

Ans. is ‘a’ i.e., Check blood counts

The most common side effect of carbimazole is maculopapular pruritic rash, while most serious adverse effect is agranulocytosis which is reversible.

Patient in the given question presents with sudden onset fever, rigors and sore throat. Infection of any site which is sudden onset and rapidly progressive in a patient on carbimazole therapy the suspicion should be development of agranulocytosis, so it is essential to do blood counts.



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