DRUG USED TO TREAT DRUG USED TO TREAT THYROID DISEASETHYROID DISEASE

ROMEL Y. FELARCA,MD,DFM.ROMEL Y. FELARCA,MD,DFM.

DIPLOMATE IN FAMILY MEDICINEDIPLOMATE IN FAMILY MEDICINE

Anatomy of Thyroid GlandAnatomy of Thyroid Gland

PhysiologyPhysiology

The primary function of the thyroid is The primary function of the thyroid is production of the production of the hormoneshormones thyroxine thyroxine (T4)(T4), , triiodothyronine (T3)triiodothyronine (T3), and , and calcitonincalcitonin. .

Up to 40% of the T4 is converted to T3 by Up to 40% of the T4 is converted to T3 by peripheral organs such as the peripheral organs such as the liverliver, , kidneykidney, and , and spleenspleen. .

T3 is about ten times more active than T4 T3 is about ten times more active than T4 (Nussey and Whitehead 2001).(Nussey and Whitehead 2001).

HypothyroidismHypothyroidism

condition marked by decreased activity of condition marked by decreased activity of the glandthe gland

commonly marked by weight gaincommonly marked by weight gain

heat intolerance heat intolerance

lethargy lethargy

constipationconstipation

hair loss hair loss

skin changesskin changes

cardiac problemscardiac problems

Hashimoto's diseaseHashimoto's diseasealso called chronic lymphocytic also called chronic lymphocytic thyroiditis, is a common cause of an thyroiditis, is a common cause of an underactive thyroid (underactive thyroid (hypothyroidismhypothyroidism).). an autoimmune disorder and causes an autoimmune disorder and causes inflammation, which impairs your inflammation, which impairs your thyroid's ability to produce hormones. thyroid's ability to produce hormones. Then, your pituitary gland attempts to Then, your pituitary gland attempts to stimulate your thyroid gland to produce stimulate your thyroid gland to produce more thyroid hormones, causing your more thyroid hormones, causing your thyroid gland to enlarge. thyroid gland to enlarge.

GoiterGoiter

GoiterGoiter

Diffuse ,solitary and multinodularDiffuse ,solitary and multinodular

Thyroid Replacement HormonesThyroid Replacement Hormones

Actions: Hypothyroidism is treated by Actions: Hypothyroidism is treated by replacing the deficient T3 and T4 replacing the deficient T3 and T4 hormones.hormones.

LevothyroxineLevothyroxine

LiothyronineLiothyronine

LiotrixLiotrix

HyperthyroidismHyperthyroidism

marked by excessive function of the marked by excessive function of the thyroid glandthyroid gland

excessive sweatingexcessive sweating

weight lossweight loss

diarrhea diarrhea

palpitations palpitations

proximal muscle weakness proximal muscle weakness

neurological changesneurological changes

Graves' diseaseGraves' diseasean autoimmune disorder, is the most common an autoimmune disorder, is the most common cause of an overactive thyroid (cause of an overactive thyroid (hyperthyroidismhyperthyroidism). ). antibodies produced by your immune system antibodies produced by your immune system stimulate the thyroid to produce too much stimulate the thyroid to produce too much thyroxine. thyroxine. Normally, your immune system uses antibodies to Normally, your immune system uses antibodies to help protect against viruses, bacteria and other help protect against viruses, bacteria and other foreign substances that invade the body. foreign substances that invade the body. In Graves' disease, antibodies mistakenly attack In Graves' disease, antibodies mistakenly attack your thyroid gland and occasionally the tissue your thyroid gland and occasionally the tissue behind your eyes and the skin of your lower legs. behind your eyes and the skin of your lower legs. The overstimulation of your thyroid in Graves' The overstimulation of your thyroid in Graves' disease results in uniform and nonpainful swelling disease results in uniform and nonpainful swelling of the gland. of the gland.

Graves diseaseGraves disease

Antithyroid MedicinesAntithyroid Medicines

Iodine 131 Iodine 131 – Is a radioactive isotope of iodine.Is a radioactive isotope of iodine.– When administered, it is absorbed into When administered, it is absorbed into

the thyroid gland in high concentrations.the thyroid gland in high concentrations.– The liberated radioactivity destroys the The liberated radioactivity destroys the

hyperactive thyroid tissue, with hyperactive thyroid tissue, with essentially no damage to other tissues essentially no damage to other tissues in the body.in the body.

– Used to treat hyperthyroidism.Used to treat hyperthyroidism.

Antithyroid DrugsAntithyroid Drugs

propylthiouracil (PTU) propylthiouracil (PTU)

methimazole (MMI, Tapazole )methimazole (MMI, Tapazole )

Carbimazole (which is converted into MMI Carbimazole (which is converted into MMI in the body) is available in Europe, but in the body) is available in Europe, but not in the United States.not in the United States.

FUNCTION OF ANTITHYROID FUNCTION OF ANTITHYROID DRUGS  DRUGS 

decrease the production and blood levels decrease the production and blood levels of thyroxine (T4) and triiodothyronine of thyroxine (T4) and triiodothyronine (T3).(T3).Antithyroid drugs require at least three Antithyroid drugs require at least three weeks (usually six to eight weeks or weeks (usually six to eight weeks or longer) to lower thyroid hormone levels longer) to lower thyroid hormone levels because they only because they only block synthesis of block synthesis of new T4 and T3new T4 and T3; they do not alter the ; they do not alter the effects of the T3 and T4 that are already effects of the T3 and T4 that are already present in the thyroid and the blood present in the thyroid and the blood stream.stream.

Side effects of PTU & MethimazoleSide effects of PTU & Methimazole

Purpuric,maculopapular rashPurpuric,maculopapular rash

Headaches,salivary gland and LN Headaches,salivary gland and LN enlargement.enlargement.

Bone marrow suppressionBone marrow suppression

HepatotoxicityHepatotoxicity

NephrotoxicityNephrotoxicity

Drug interactionsDrug interactions

WarfarinWarfarin– Reduce dosage of anticoagulantsReduce dosage of anticoagulants

DigoxinDigoxin– Increase dosage of digoxinIncrease dosage of digoxin

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