Anti thyroid medicationsNuwan GunapalaRegistrar WD 21/40B

Overview Thyroid physiologyTreatment options

◦Thyoamides◦Iodide◦Steroids◦Lithium◦Other drugs

Thyroid physiologyThyroid hormones are iodine

containing amino acidsDietary Iodide are absorbed and

transfer in to thyroid.Some of iodide secret via bile

and reabsorb through enterohepatic circulation

Iodide enters to thyrocytes via sodium iodide symporter

Iodide enters to colloid through apical membrane via a transporter called pendrin

Thyroid peroxidase enzyme located at apical membrane of thyrocytes convert iodide to iodine and attach it to globulin - iodotyrosines

Iodotyrosines condensed to form tri and tetra iodotyrosines – thyroid peroxidase

When there is a need these T4 and T3 molecules released in to blood.

Thyoamides Mechanism of action

◦Inhibit thyroid peroxidase and prevents organification of iodine and condensation of iodotyrosines

Propylthiouracyl also inhibit peripheral conversion of T3

Thioamides CarbimazoleMethimazolePropylthiouracilMethylthiouracil

Characteristics of thioamides

Results appear later – 3 to 4 wks symptoms relieved and 3 to 4 mts BMR normalize

Long term results in thyroid hyperplasia

Methimazole is potent 10 times as propylthiouracil

Propylthiouracil is preferable in pregnancy:◦ It crosses the placenta less readily◦ Is not secreted in breast milk

Propylthiouracil has an early onset of action, so use in thyroid storm

Adverse reactions

1. Long-term use leads to thyroid hyperplasia;

2. Pruritic maculopapular rash is the most common

adverse reaction

3. The severe adverse reaction is agranulocytosis

IodideIn pharmacologic doses the major action

is to inhibit hormone release(Wolff–Chaikoff effect)

Improvement in thyrotoxic symptoms occurs within 2 -7 days, after that escape mechanism

Decrease of size & vascularity of the hyperplastic gland

Iodides in pregnancy should be avoided, since they cross the placenta and can cause fetal goiter

Clinical use

Treatment of hyperthyroidism

1. Operation preparation

2. Thyroid crisis.

Adverse reactions

1.Rash

2. Swollen salivary glands, mucous

membrane ulcerations

Lithium Reduce secretion of thyroglobulin in

to colloidAlso reduce release of hormones

from throglobulin in to circulation Indications

◦elevation of transaminases◦agranulocytosis ◦allergic reaction◦resistance to propylthiouracil therapy

Steroides Corticosteroids reduce T4 to

T3 conversion and possibly affect the autoimmune process in Graves’ disease

Use in Graves disease and thyroid storm

Also use in graves eye disease

Other drugsAmioderoneBarbiturates accelerate T4

breakdown (by enzyme induction) and are also sedative

Because thyrotoxic patients have an increased thyroid hormone enterohepatic circulation, cholesteramine has a role in treatment

Symptoms controlling drugsPropranolol will control

tachycardia, hypertension, and atrial fibrillation

Diltiazem, can control tachycardia in patients in whom beta-blockers are contraindicated