Endocrinology Book

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Antithyroid Drug

Aka: Antithyroid Drug, Thioamide, Thionamide, Propylthiouracil, PTU, Methimazole, Tapazole
  1. See Also
    1. Hyperthyroidism
    2. Hyperthyroidism Management
  2. Indications
    1. Hyperthyroidism in children and adolescents
    2. Pregnancy (PTU)
    3. Severe Grave's Disease (e.g. Thyroid Storm)
    4. Subclinical Hyperthyroidism
  3. Mechanism
    1. Thionamides block T3 and T4 synthesis (by inhibiting Thyroid peroxidase)
  4. Dose: Grave's Disease
    1. Target dose to Free T4 high end of normal range
    2. Methimazole (Tapazole)
      1. Preferred first-line agent
      2. Advantages over Propylthiouracil (PTU)
        1. Once daily dosing
        2. Decreases T4 and T3 levels more rapidly
        3. Much safer than PTU
          1. Lower risk of Agranulocytosis at moderate doses
          2. Does not carry the same liver toxicity risk as PTU
      3. Dosing: Hyperthyroidism
        1. Start: 10-30 mg PO qd
        2. Titrate Methimazole dose down after 4-6 weeks
          1. Goal: maintain normal Thyroid function
          2. Dose: reduce to 5-10 mg per day
      4. Dosing: Other
        1. Subclinical Hyperthyroidism: 5 mg PO qd
    3. Propylthiouracil (PTU)
      1. Indications (reasons to use PTU instead of Methimazole)
        1. Lactation
        2. Pregnancy (both PTU and Methimazole are Category D)
          1. Use PTU in first trimester
          2. Use Methimazole in second and third trimester
      2. Dosing: Hyperthyroidism
        1. Start: 100 mg po tid
        2. Maximum: 150 mg every 6-8 hours
        3. Titrate PTU dose down after 4-6 weeks
          1. Goal: maintain normal Thyroid function
          2. Dose: reduce to 50-100 mg per day
      3. Dosing: Other
        1. Thyroid Storm: 1 gram load, then 300 mg PO q6 hours
        2. Subclinical Hyperthyroidism: 50-100 mg PO qd
  5. Adverse effects (3 per 1000 patients)
    1. Drug-Induced Agranulocytosis (more common with PTU)
      1. Risk increases over age 40 years
      2. Occurs in 0.17% of those on Methimazole
      3. Presentation: Infection (e.g. Pharyngitis)
      4. Course
        1. Resolves within 2-3 weeks after drug stopped
        2. Severe, refractory course may occur
      5. Contraindication to further Antithyroid Drugs
    2. Jaundice
      1. Cholestatic Jaundice
      2. Occurs more commonly with Methimazole
    3. Hepatitis
      1. Occurs with both Methimazole and Propylthiouracil (PTU)
      2. Methimazole associated hepatitis
        1. Incidence: 3.17 per 1000 person-years
        2. Acute Hepatic Failure: 0.32 per 1000 person-years
      3. Propylthiouracil (PTU) is associated with severe liver injury
        1. Adults: 1 in 10,000
        2. Children: 1 in 2,000
    4. Vasculitis
    5. Lupus-like syndrome
    6. Aplastic Anemia
    7. Rash or Pruritus
      1. Switch from PTU to Methimazole if severe
    8. Arthralgia or Polyarthritis
    9. Fever
    10. Congenital abnormalities possible with Methimazole
  6. Monitoring
    1. Repeat examination every 3 months
    2. Pregnancy Test before starting therapy
    3. Lab Testing while on antithyroid medications: Monthly for 6 to 12 months
      1. Complete Blood Count (CBC)
        1. Obtain at baseline
        2. Repeat if Pharyngitis or fever occur (need not be done without symptoms or signs)
      2. Liver Function Tests
        1. Obtain at baseline and if symptoms develop
      3. Thyroid Function Tests (baseline, then every 4-8 weeks, then after stabilizing, every 3 months)
        1. Thyroid Stimulating Hormone (TSH) after stabilizing, once on every 3 month schedule
        2. Free T4
        3. Free T3
    4. Lab Testing after completing antithyroid medications
      1. Obtain Thyroid Function Tests every 1-3 months for 6-12 months
    5. Indications to discontinue medication (via taper)
      1. Total treatment course of 12-18 months AND
      2. TSH normalized for 6-12 months
    6. Indications to consider Thyroid ablation
      1. Inadequate suppression at 12 months from initiation
  7. Efficacy: Predictors of Relapse (occurs in 30-70% of cases within first year)
    1. Tobacco abuse
    2. Large Goiter
    3. Thyroid Stmulating Antibody high at end of treatment
  8. References
    1. Kravets (2016) Am Fam Physician 93(5): 363-70 [PubMed]
Medication Costs
propylthiouracil (on 5/17/2017 at Medicaid.Gov Pharmacy Drug pricing)
PROPYLTHIOURACIL 50 MG TABLET Generic $0.62 each
methimazole (on 5/17/2017 at Medicaid.Gov Pharmacy Drug pricing)
METHIMAZOLE 10 MG TABLET Generic $0.13 each
METHIMAZOLE 5 MG TABLET Generic $0.11 each
FPNotebook does not benefit financially from showing this medication data or their pharmacy links. This information is provided only to help medical providers and their patients see relative costs. Insurance plans negotiate lower medication prices with suppliers. Prices shown here are out of pocket, non-negotiated rates. See Needy Meds for financial assistance information.

Methimazole (C0025644)

Definition (MSH) A thioureylene antithyroid agent that inhibits the formation of thyroid hormones by interfering with the incorporation of iodine into tyrosyl residues of thyroglobulin. This is done by interfering with the oxidation of iodide ion and iodotyrosyl groups through inhibition of the peroxidase enzyme.
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D008713
SnomedCT 37656002, 404864000
LNC LP18583-2, MTHU004698
English 1 Methyl 2 mercaptoimidazole, 1-Methyl-2-mercaptoimidazole, Mercasolyl, Mercazolyl, Merkazolil, Methimazole, Methylmercaptoimidazole, Methymazol, Thiamazole, Thimazol, Tiamazol, 2H-Imidazole-2-thione, 1,3-dihydro-1-methyl-, methimazole, METHIMAZOLE, Methimazole preparation, methimazole (medication), Methimazole [Chemical/Ingredient], tiamazol, thiamazole, Methimazole (substance), Methimazole (product), Thiamazole preparation
Swedish Metimazol
Spanish preparado de metimazol, metimazol (sustancia), metimazol, preparado de metimazol (sustancia), preparado de tiamazol, metimazol (producto), Metimazol, Tiamazol
Czech methimazol
Finnish Metimatsoli
Russian METIMAZOL, MERKAZOLIL, TIMAZOL, МЕРКАЗОЛИЛ, МЕТИМАЗОЛ, ТИМАЗОЛ
Japanese チアマゾール, メルカプトメチルイミダゾール, メルカゾール, チマゾール, メチマゾール
Croatian METIMAZOL
Polish Metimazol
French Thiamazol, Thiamazole
German Methimazol, Methymazol, Thiamazol
Italian Metimazolo
Portuguese Metimazol, Tiamazol
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Propylthiouracil (C0033511)

Definition (NCI) A thiourea derivative with antithyroid property. Propylthiouracil (PTU) interferes with the oxidation of iodine possibly by interaction with peroxidase or a peroxidase-mediated complex reaction, thereby inhibiting synthesis of thyroid hormones tri-iodothyronine (T3) and thyroxine (T4). In addition, this agent inhibits the Type I 5'-deiodinase (D1), an enzyme involved in the peripheral conversion of thyroxine to tri-iodothyronine. This results in decreased plasma triodothyronine concentrations and decreased entrance of thyroxine into cells thereby reducing thyroid hormone activity.
Definition (MSH) A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534)
Definition (PDQ) A thiourea derivative with antithyroid property. Propylthiouracil (PTU) interferes with the oxidation of iodine possibly by interaction with peroxidase or a peroxidase-mediated complex reaction, thereby inhibiting synthesis of thyroid hormones tri-iodothyronine (T3) and thyroxine (T4). In addition, this agent inhibits the Type I 5'-deiodinase (D1), an enzyme involved in the peripheral conversion of thyroxine to tri-iodothyronine. This results in decreased plasma triodothyronine concentrations and decreased entrance of thyroxine into cells thereby reducing thyroid hormone activity. Check for "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=39288&idtype=1" active clinical trials or "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=39288&idtype=1&closed=1" closed clinical trials using this agent. ("http://nciterms.nci.nih.gov:80/NCIBrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&code=C781" NCI Thesaurus)
Concepts Pharmacologic Substance (T121) , Nucleic Acid, Nucleoside, or Nucleotide (T114)
MSH D011441
SnomedCT 3814009, 387203007
LNC LP17868-8, MTHU012366
English 6-Propyl-2-Thiouracil, Propylthiouracil, 4(1H)-Pyrimidinone, 2,3-dihydro-6-propyl-2-thioxo-, 6 Propyl 2 Thiouracil, propylthiouracil, Propylthiouracil preparation, anti-thyroid agents propylthiouracil (propylthiouracil), propylthiouracil (medication), PTU (propylthiouracil), PROPYLTHIOURACIL, Propylthiouracil [Chemical/Ingredient], 6-Propyl-2-thiouracil, PTU preparation, Propylthiouracil product, Propylthiouracil (product), Propylthiouracil (substance)
Swedish Propyltiouracil
Spanish preparado de propiltiouracilo, preparado de PTU, preparado de propiltiouracilo (producto), preparado de propiltiouracilo (sustancia), propiltiouracilo (producto), propiltiouracilo (sustancia), propiltiouracilo, Propiltiouracilo
Czech propylthiouracil
Finnish Propyylitiourasiili
Russian PROPILTIOURATSIL, ПРОПИЛТИОУРАЦИЛ
Polish Propylotiouracyl
Japanese チウラジール, プロピルチオウラシル, プロパジール
French Propylthiouracile
German Propylthiouracil
Italian Propiltiouracile
Portuguese Propiltiouracila
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Thioamides (C0039875)

Definition (CSP) compounds of the type R-(C=S)-N=.
Definition (MSH) Organic compounds containing the radical -CSNH2.
Concepts Organic Chemical (T109)
MSH D013854
SnomedCT 406762005
English Thioamides, Thioamides [Chemical/Ingredient], thioamides, thioamide, Thioamide (substance), Thioamide
Swedish Tioamider
Czech thioamidy
Finnish Tioamidit
Russian TIOAMIDY, ТИОАМИДЫ
Polish Tioamidy
Spanish tioamida (sustancia), tioamida, Tioamidas
French Thioamides
German Thioamide
Italian Tioamidi
Portuguese Tioamidas
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Antithyroid Agents (C0040125)

Definition (MSH) Agents that are used to treat hyperthyroidism by reducing the excessive production of thyroid hormones.
Definition (CSP) any agent or substance which suppresses, prevents or opposes the biosynthesis of thyroid hormones.
Concepts Pharmacologic Substance (T121) , Hormone (T125)
MSH D013956
SnomedCT 5067008, 418416001
English Antagonists, Thyroid, Antithyroid Drugs, Drugs, Antithyroid, Thyroid Antagonists, thyroid inhibitor, Agents, Antithyroid, Antithyroid Agents, THYROID ANTAG, ANTITHYROID AGENTS, anti-thyroid agents, anti-thyroid agents (medication), thyroid antagonists, [HS852] ANTITHYROID AGENTS, antithyroid drug, inhibitors thyroid, antithyroid agents, antithyroid preparations, antithyroid drugs, Thyroid Antagonist, ANTITHYROID PREPARATIONS, Thyroid antagonists, Antithyroid drugs, Antithyroid agent (product), Antithyroid agent, Thyroid inhibitor preparation, antithyroid agent, Antithyroid preparation, NOS, Thyroid inhibitor preparation, NOS, Antithyroid Agent, Antithyroid agent (substance)
Spanish agente antitiroideo (sustancia), agente antitiroideo, Antitiroideos, Agentes Antitiroideos, Efecto Antitiroideo, preparado antitiroideo (producto), preparado antitiroideo (sustancia), preparado antitiroideo, preparado inhibidor tiroideo, Antagonistas Tiroideos
French Anti-thyroïdiens, Agents antithyroïdiens, Thyréostatiques, Médicaments antithyroïdiens, Agents anti-thyroïdiens, Médicaments anti-thyroïdiens, Antithyroïdiens
Swedish Tyreostatika
Czech thyreostatika, tyreostatika, antithyreoidní látky
Finnish Tyreostaatit
Italian Sostanze antitiroidee, Antagonisti tiroidei, Farmaci antitiroidei
Russian TIREOIDNYKH GORMONOV ANTAGONISTY, STRUMOGENNYE FAKTORY, ANTITIREOIDNYE VESHCHESTVA, АНТИТИРЕОИДНЫЕ ВЕЩЕСТВА, СТРУМОГЕННЫЕ ФАКТОРЫ, ТИРЕОИДНЫХ ГОРМОНОВ АНТАГОНИСТЫ
Japanese 甲状腺拮抗物質, 抗甲状腺薬, 甲状腺腫誘発物質, 抗甲状腺剤, 甲状腺きっ抗剤
Croatian ANTITIREOIDNE TVARI
Polish Tyreostatyki, Goitrogeny, Środki przeciwtarczycowe, Strumigeny
Portuguese Antitireóideos, Antitireoidianos, Efeito Antitireóideo, Agentes Antitireoidianos, Agentes Antitireóideos, Antagonistas Tireóideos
Norwegian Thyreoideaantagonister, Antithyreoideapreparater, Tyreostatika
German Antithyreodika, Thyreostatika
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Tapazole (C0728778)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D008713
English tapazole, Tapazole, Eli Lilly Brand of Methimazole, Jones Brand of Methimazole
Sources
Derived from the NIH UMLS (Unified Medical Language System)


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