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| Clinical data | |
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| Trade names | Neo-Mercazole, Anti-Thyrox, etc. |
| AHFS/Drugs.com | International Drug Names |
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| Routes of administration | By mouth |
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| Pharmacokinetic data | |
| Protein binding | 85% |
| Eliminationhalf-life | 5.3h |
| Excretion | Kidney >90% |
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| CompTox Dashboard(EPA) | |
| ECHA InfoCard | 100.040.762 |
| Chemical and physical data | |
| Formula | C7H10N2O2S |
| Molar mass | 186.23 g·mol−1 |
| 3D model (JSmol) | |
| Melting point | 122 to 125 °C (252 to 257 °F) |
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Carbimazole (brand names Neo-Mercazole, Anti-Thyrox, etc.) is used to treathyperthyroidism. Carbimazole is apro-drug as after absorption it is converted to the active form,methimazole. Methimazole preventsthyroid peroxidase enzyme from iodinating and coupling thetyrosine residues onthyroglobulin, hence reducing the production of the thyroid hormonesT3 and T4 (thyroxine).
It is on theWorld Health Organization's List of Essential Medicines.[2]
Medical therapy for hyperthyroidism typically involves either titrating the dose of carbimazole until the patient becomes euthyroid or maintaining a high dose of carbimazole to suppress endogenous thyroid production, and then replacing thyroid hormone with levothyroxine ("block and replace"). Treatment is usually given for 18–24 months followed by a trial withdraw.[3]
The onset of anti-thyroid effect is rapid but the onset of clinical effects on thyroid hormone levels in the blood is much slower. This is because the large store of pre-formed T3 and T4 in the thyroid gland and bound tothyroid binding globulin (99% bound) has to be depleted before any beneficial clinical effect occurs.
Whilstrashes andpruritus are common, these can often be treated withantihistamines without stopping the carbimazole. For those patients where sensitivity reactions cannot be controlled,propylthiouracil may be used as an alternative; cross-sensitivity between these drugs is rare.
Its most serious rare side effect isbone marrow suppression causingneutropenia andagranulocytosis. This may occur at any stage during treatment and without warning; monitoring of white cell count is not useful. Patients are advised to immediately report symptoms of infection, such assore throat or fever, so that afull blood count test may be arranged. If this confirms a low neutrophil count, discontinuation of the drug leads to recovery. However failure to report suggestive symptoms or delays in considering the possibility of immunosuppression and its testing, can lead to fatalities.
Some people are allergic toazole(s). Some azole drugs have adverseside-effects. Some azole drugs may disruptestrogen production inpregnancy, affecting pregnancy outcome.[4][verification needed]
Carbimazole should be used judiciously in pregnancy as it crosses the placenta. It has (rarely) been associated with congenital defects, includingaplasia cutis of the neonate but is not contra-indicated. However, it more predictably may cause fetalhypothyroidism so (in minimal doses) it can be used in order to control maternalhyperthyroidism. There are reported cases of goiter andchoanal atresia in fetus.[5] Furthermore, breast feeding is possible but only if lowest effective dose is used and neonatal development is closely monitored.
For the above reasons, it is preferable to usePTU in pregnancy, especially in the first trimester, with the possibility of changing to carbimazole for the second and third trimesters.[6]
