Methimazole

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Methimazole
Systematic (IUPAC) name
1-methyl-3H-imidazole-2-thione
Identifiers
CAS number	60-56-0
ATC code	?
PubChem	1349907
DrugBank	APRD00002
Chemical data
Formula	C4H6N2S
Mol. mass	114.17 g/mol
Physical data
Melt. point	146 °C (295 °F)
Solubility in water	2.75 mg/mL (20 °C)
Pharmacokinetic data
Bioavailability	93%
Protein binding	None
Metabolism	Hepatic
Half life	5-6 hours
Excretion	Renal
Therapeutic considerations
Pregnancy cat.	D (US)
Legal status	℞-only(US)
Routes	Oral

Methimazole is an antithyroid drug similar in action to propylthiouracil, and part of the thioamide group.

Contents 1 Indications 2 Mechanisms of Action 3 Adverse Effects 3.1 General Side Effects 4 Drug Warnings 4.1 Before taking Methimazole

[edit] 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 is also taken before thyroid surgery or radioactive iodine therapy, to lower thyroid hormone levels and minimize the effects of thyroid manipulation.

[edit] Mechanisms of Action

Thioamides inhibit many steps in the synthesis of thyroid hormones, including the addition of iodide to thyroglobulin by the enzyme thyroperoxidase, a necessary step in the synthesis of thyroxine.

Notably, they do 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.

[edit] Adverse Effects

Healthcare providers need to be notified immediately if fever or sore throat develop 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 (specifically, neutropenia, which indicates a deficiency of neutrophils). A complete blood count (CBC) with differential is required to confirm the suspicion, and the drug discontinued.

[edit] General Side Effects

Although side effects from methimazole are not common (~5%), they can occur. Tell your healthcare provider if any of these symptoms are severe or persist:

• 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 platelets

Experiencing sore throat, fever, headache, chills, unusual bleeding, skin eruptions or jaundice requires patients to notify treating physician.

[edit] Drug Warnings

[edit] Before taking Methimazole

• Tell your healthcare provider and pharmacist if you are allergic to methimazole, propylthiouracil, lactose, or any other drugs.
• Tell your healthcare provider and pharmacist what prescription and nonprescription medications you are taking, especially anticoagulants ('blood thinners') such as warfarin (Coumadin), beta blockers such as propranolol (Inderal), diabetes medications, digoxin (Lanoxin), theophylline (Theobid, Theo-Dur), and vitamins.
• Tell your healthcare provider if you have or have ever had any blood disease, such as decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia), or aplastic anemia, or liver disease (hepatitis, jaundice).
• Tell your healthcare provider if you are pregnant, plan to become pregnant, or are breast-feeding. An alterntive anti-thyroid drug, propylthiouracil is often substituted during pregnancy or breast-feeding. If you become pregnant while taking methimazole, discuss with your healthcare provider whether you should switch to propylthiouracil with your healthcare provider. Early studies suggested that methimazole may harm the fetus, although more recent studies suggest this may not be the case.
• If you are having surgery, including dental surgery, tell the healthcare provider or dentist that you are taking Methimazole.