Carbimazole
Encyclopedia
Carbimazole is used to treat hyperthyroidism
. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole
. Methimazole prevents the thyroid peroxidase
enzyme from coupling and iodinating the tyrosine residues on thyroglobulin
, hence reducing the production of the thyroid hormones T3 and T4 (thyroxine
).
, and then reduced to a maintenance dose of 5 - 15mg. Treatment is usually given for 12 - 18 months followed by a trial withdraw.
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 to Thyroid Binding Globulin (99% bound) has to be depleted before any beneficial clinical effect occurs.
(s).
Some azole drugs have adverse side-effects.
Some azole drugs may disrupt estrogen
production in pregnancy
, affecting pregnancy outcome.
http://informahealthcare.com/doi/abs/10.1081/ERC-120015045?cookieSet=1&journalCode=erc
es and pruritus are common, these can often be treated with antihistamine
s without stopping the carbimazole. For those patients where sensitivity reactions can not be controlled, propylthiouracil
may be used as an alternative.
Its most serious rare side effect is bone marrow suppression
causing neutropenia
and agranulocytosis
. This may occur at any stage during treatment and without warning. Patients are advised to immediately report symptoms of infection, especially sore throats
, so that a full blood count test may be arranged. If this confirms a low neutrophil count then the drug must be discontinued immediately, allowing for usually a prompt recovery. However failure to report suggestive symptoms or delays in considering the possibility of immunosuppression and its testing, can lead to fatalities.
Should be used with caution in pregnancy as crosses the placenta barrier.
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole
Methimazole
Methimazole is an antithyroid drug, and part of the thioamide group.-Indications:...
. Methimazole prevents the thyroid peroxidase
Thyroid peroxidase
Thyroid peroxidase or thyroperoxidase is an enzyme expressed mainly in the thyroid that liberates iodine for addition onto tyrosine residues on thyroglobulin for the production of thyroxine or triiodothyronine , thyroid hormones. In humans, thyroperoxidase is encoded by the TPO...
enzyme from coupling and iodinating the tyrosine residues on thyroglobulin
Thyroglobulin
Thyroglobulin is a 660 kDa, dimeric protein produced by and used entirely within the thyroid gland. In earlier literature, Tg was referred to as colloid....
, hence reducing the production of the thyroid hormones T3 and T4 (thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
).
Clinical use
Therapy for hyperthyroidism generally starts at a high daily dose of 15 - 40mg continued until the patient has normal thyroid functionThyroid function tests
Thyroid function tests is a collective term for blood tests used to check the function of the thyroid.TFTs may be requested if a patient is thought to suffer from hyperthyroidism or hypothyroidism , or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy...
, and then reduced to a maintenance dose of 5 - 15mg. Treatment is usually given for 12 - 18 months followed by a trial withdraw.
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 to Thyroid Binding Globulin (99% bound) has to be depleted before any beneficial clinical effect occurs.
Precautions
Some people are allergic to azoleAzole
An azole is a class of five-membered nitrogen heterocyclic ring compounds containing at least one other non-carbon atom of either nitrogen, sulfur, or oxygen. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs with fewer...
(s).
Some azole drugs have adverse side-effects.
Some azole drugs may disrupt estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
production in pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, affecting pregnancy outcome.
http://informahealthcare.com/doi/abs/10.1081/ERC-120015045?cookieSet=1&journalCode=erc
Side Effects
Whilst rashRash
A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...
es and pruritus are common, these can often be treated with antihistamine
Antihistamine
An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...
s without stopping the carbimazole. For those patients where sensitivity reactions can not be controlled, propylthiouracil
Propylthiouracil
Propylthiouracil or 6-n-Propylthiouracil is a thioamide drug used to treat hyperthyroidism by decreasing the amount of thyroid hormone produced by the thyroid gland...
may be used as an alternative.
Its most serious rare side effect is bone marrow suppression
Bone marrow suppression
Bone marrow suppression or myelotoxicity or myelosuppression, is the decrease in cells responsible for providing immunity, carrying oxygen, and those responsible for normal blood clotting is a serious side effect of chemotherapy and certain drugs affecting the immune system such as azathioprine...
causing neutropenia
Neutropenia
Neutropenia, from Latin prefix neutro- and Greek suffix -πενία , is a granulocyte disorder characterized by an abnormally low number of neutrophils, the most important type of white blood cell...
and agranulocytosis
Agranulocytosis
Granulopenia, also known as Agranulosis or Agranulocytosis, is an acute condition involving a severe and dangerous leukopenia , most commonly of neutrophils causing a neutropenia in the circulating blood. It represents a severe lack of one major class of infection-fighting white blood cells...
. This may occur at any stage during treatment and without warning. Patients are advised to immediately report symptoms of infection, especially sore throats
Pharyngitis
Pharyngitis is an inflammation of the throat or pharynx. In most cases it is quite painful, and is the most common cause of a sore throat.Like many types of inflammation, pharyngitis can be acute – characterized by a rapid onset and typically a relatively short course – or chronic....
, so that a full blood count test may be arranged. If this confirms a low neutrophil count then the drug must be discontinued immediately, allowing for usually a prompt recovery. However failure to report suggestive symptoms or delays in considering the possibility of immunosuppression and its testing, can lead to fatalities.
Should be used with caution in pregnancy as crosses the placenta barrier.