Carbimazole

Registered South African indications:

• Hyperthyroidism
• Thyrotoxicosis
• Preparation for thyroidectomy
• Treatment prior to and post radio-active ablative therapy

Contraindications

• Hypersensitivity to the active ingredient or any of its excipients
• Severe hepatic impairment
• Serious pre-existing haematological conditions

Cautions

• Pregnancy
• Breastfeeding
• Renal impairment
• Mild to moderate hepatic impairment
• Confusion or poor memory
• Intrathoracic goitre
• Women of child-bearing age
• Galactose intolerance
• Lapp lactase deficiency
• Glucose-galactose malabsorption

Forms avail. in SA and covered in this monograph: tab

Hyperthyroidism
Preparation for thyroidectomy in hyperthyroidism
Preparation for, and as concomitant therapy with, radio-iodine treatment

• Oral (tab): Initial: 20-60mg, dly; Titrate against thyroid function until patient euthyroid; Maintenance: 5-15mg, dly; Treatment duration: 6-18 months

Serial thyroid function monitoring is recommended in order to maintain a euthyroid state

Paed. forms avail. in SA and covered in this monograph: tab

Hyperthyroidism
Preparation for thyroidectomy in hyperthyroidism
Preparation for, and as concomitant therapy with, radio-iodine treatment

• Oral (tab): Initial: 15mg, dly; Titrate against thyroid function until patient euthyroid

Serial thyroid function monitoring is recommended in order to maintain a euthyroid state

Pregnancy

• Caution; positive evidence of risk in studies
• Carbimazole crosses the placenta but, provided the mother's dose is within the standard range, and her thyroid status is monitored; there is no evidence of neonatal thyroid abnormalities. Studies have shown that the incidence of congenital malformations is greater in the children of mothers whose hyperthyroidism has remained untreated than in those to whom treatment with carbimazole has been given
• However, very rare cases of congenital malformations have been observed following the use of carbimazole or its active metabolite methimazole during pregnancy. A causal relationship of these malformations, especially choanal atresia and aplasia cutis congenital, to transplacental exposure to carbimazole and methimazole cannot be excluded. Therefore, the use of carbimazole in non-pregnant women of childbearing potential should be based on individual risk/benefit assessment
• Cases of renal, skull, cardiovascular congenital defects, exomphalos, gastrointestinal malformation, umbilical malformation and duodenal atresia have also been reported. Therefore, carbimazole should be used in pregnancy only when no alternative is available. If carbimazole is used in pregnancy the dose of carbimazole must be regulated by the patient's clinical condition. The lowest dose possible should be used, and this can often be discontinued three to four weeks before term, in order to reduce the risk of neonatal complications. The blocking-replacement regimen should not be used during pregnancy since very little thyroxine crosses the placenta in the last trimester

Breastfeeding

• Caution; not recommended
• Carbimazole is secreted in breast milk and, if treatment is continued during lactation, the patient should not continue to breastfeed her baby

Renal Impairment

• Caution; no information available

Hepatic Impairment

• Mild to moderate: Caution; no dose adjustment recommended
• Severe: Contraindicated

Elderly

• No dose adjustment recommended

Porphyria Information

• Not yet classified (NC)

Drugs in Sport

• Permitted - No warnings

Central Nervous System Disorders

• Headache
• Neuritis
• Polyneuropathy
• Malaise

Gastrointestinal Disorders

• Nausea
• Mild gastric distress
• Ageusia
• Acute salivary gland swelling

Hepatobiliary Disorders

• Abnormal hepatic function tests
• Hepatitis
• Cholestatic hepatitis
• Cholestatic jaundice 
• Jaundice

Endocrine and Metabolic Disorders

• Insulin autoimmune syndrome

Musculoskeletal Disorders

• Myopathy
• Myalgia

Skin and Subcutaneous Tissue Disorders

• Bruising
• Skin rash
• Pruritus
• Urticaria
• Hair loss 
• Stevens-Johnson syndrome

Immune, Blood and Lymphatic System Disorders

• Fever
• Neutropenia
• Eosinophilia
• Leukopenia
• Agranulocytosis 
• Aplastic anaemia 
• Thrombocytopenia
• Haemolytic anaemia
• Generalised lymphadenopathy
• Angioedema
• Multi-system hypersensitivity reactions
• Bleeding

• Agents inducing agranulocytosis
• Anticoagulants
• Theophylline

• Thyroid function

Specific cases may require

•  Serum creatine phosphokinase

Carbimazole is rapidly metabolised to methimazole. Methimazole reduces the production of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) by preventing the thyroid peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin.

Tablet 5mg

• Neo-Mercazole (Pharmacare)