Methimazole
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Methimazole
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| Systematic (IUPAC) name | |
| 1-methyl-3H-imidazole-2-thione | |
| Identifiers | |
| CAS number | |
| ATC code | ? |
| PubChem | |
| DrugBank | |
| 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 | |
| Routes | Oral |
Methimazole (also known as Tapazole) is an antithyroid drug similar in action to propylthiouracil, and part of the thioamide group.
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[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] Mechanism 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
Although side effects from methimazole are not common (~5%), they can occur. 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, 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 platelets
[edit] Drug interactions
[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 alternative 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. 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.
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