Methimazole

Not to be confused with metamizole .

Methimazole

Systematic (IUPAC) name
1-methyl-3H-imidazole-2-thione
Clinical data
AHFS/Drugs.com	monograph
MedlinePlus	a682464
Pregnancy cat.	D (US)
Legal status	℞-only (US)
Routes	Oral
Pharmacokinetic data
Bioavailability	93%
Protein binding	None
Metabolism	Hepatic
Half-life	5-6 hours
Excretion	Renal
Identifiers
CAS number	60-56-0 Y
ATC code	H03BB02
PubChem	CID 1349907
DrugBank	APRD00002
ChemSpider	1131173 Y
UNII	554Z48XN5E Y
KEGG	D00401 Y
ChEBI	CHEBI:50673 Y
ChEMBL	CHEMBL1515 Y
Chemical data
Formula	C4H6N2S
Mol. mass	114.17 g/mol
SMILES	eMolecules & PubChem
InChI InChI=1S/C4H6N2S/c1-6-3-2-5-4(6)7/h2-3H,1H3,(H,5,7) Y Key:PMRYVIKBURPHAH-UHFFFAOYSA-N Y
Physical data
Melt. point	146 °C (295 °F)
Solubility in water	2.75 mg/mL (20 °C)
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Methimazole (also known as Tapazole or Thiamazole or MMI) is an antithyroid drug^[1], and part of the thioamide group.

Indications

Methimazole is a drug used to treat hyperthyroidism, a condition that usually occurs when the thyroid gland is producing too much thyroid hormone. It may also be taken before thyroid surgery to lower thyroid hormone levels and minimize the effects of thyroid manipulation.

Mechanism of action

Methimazole inhibits the addition of iodine to thyroglobulin by the enzyme thyroperoxidase, a necessary step in the synthesis of triiodothyronine (T3) and thyroxine (T4).

It does not inhibit the action of the sodium-dependent iodide transporter located on follicular cells' basolateral membranes. Inhibition of this step requires competitive inhibitors such as perchlorate and thiocyanate.

It acts at CXCL10.^[2]

Adverse effects

It is important to monitor any symptoms of fever or sore throat while taking methimazole; this could indicate the development of agranulocytosis, an uncommon but severe side effect resulting from a drop in the white blood cell count (to be specific, neutropenia, a deficiency of neutrophils). A complete blood count (CBC) with differential is performed to confirm the suspicion, in which case the drug is discontinued. Administration of recombinant human granulocyte colony-stimulating factor (rhG-CSF) may increase recovery.

Other side effects include

• skin rash
• itching
• abnormal hair loss
• upset stomach
• vomiting
• loss of taste
• abnormal sensations (tingling, prickling, burning, tightness, and pulling)
• swelling
• joint and muscle pain
• drowsiness
• dizziness
• decreased white blood cells
• decreased platelet
• Aplasia cutis congenita (prenatal exposure)

Drug interactions

Adverse effects may occur for individuals who:

• Take anticoagulants ('blood thinners') such as warfarin (Coumadin), diabetes medications, digoxin (Lanoxin), theophylline (Theobid, Theo-Dur), and vitamins
• Have ever had any blood disease, such as decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia), or aplastic anemia, or liver disease (hepatitis, jaundice)
• Are pregnant, or going to become pregnant, or are breast-feeding. An alternative anti-thyroid drug, propylthiouracil, is often substituted during pregnancy or breast-feeding. If pregnancy occurs while taking methimazole, switching to propylthiouracil may be an alternative. Early studies suggested that methimazole may harm the fetus; however, more recent studies suggest this may not be the case.^{[citation needed]}
• Are going to have surgery, including dental surgery.

See also

• Graves' disease

References

1. ^ Nakamura H, Noh JY, Itoh K, Fukata S, Miyauchi A, Hamada N (June 2007). "Comparison of methimazole and propylthiouracil in patients with hyperthyroidism caused by Graves' disease". The Journal of clinical endocrinology and metabolism 92 (6): 2157–62. doi:10.1210/jc.2006-2135. PMID 17389704. http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=17389704. 
2. ^ Crescioli C, Cosmi L, Borgogni E, et al. (October 2007). "Methimazole inhibits CXC chemokine ligand 10 secretion in human thyrocytes". J. Endocrinol. 195 (1): 145–55. doi:10.1677/JOE-07-0240. PMID 17911406. http://joe.endocrinology-journals.org/cgi/pmidlookup?view=long&pmid=17911406.