Vidalta tablets are used to control over active thyroid glands (hyperthyroidism). This is a common condition of older cats, though it is unusual in young cats. Hyperthyroidism develops spontaneously over a period of time and results in a number of symptoms. Typically affected cats lose weight despite eating well. They may behave in a slightly agitated or over-active way, and will tend to have a fast heart rate, even when at rest. They may show vomiting or diarrhoea too. Vidalta tablets are designed to reduce the excess production of thyroid hormone from the thyroid glands. Vidalta are classed as a sustained release type of tablet. This helps to maintain their effectiveness over the whole day. It is important to try and give Vidalta tablets to cats whole, not crushed, for this to work most effectively.
Vidalta tablets can show side effects sometimes, such as vomiting or diarrhoea. Occasionally they cause dermatitis of the face and neck, resulting in small, itchy, sore patches. It might be necessary to reduce the dose or stop treatment if side effects are seen, so veterinary advice needs to be taken.
Each 10 mg prolonged-release tablet contains:
Active substance: Carbimazole 10.00 mg
Excipients: Red ferric oxide (E172) 0.25 mg
Each 15 mg prolonged-release tablet contains:
Active substance: Carbimazole15.00 mg
Excipients: Red ferric oxide (E172) 0.75 mg
For full list of excipients see Section “Pharmaceutical particulars”.
10 mg prolonged-release tablets: Round pink tablet with little spots.
15 mg prolonged-release tablets: Round dark pink tablet with little spots.
Treatment of hyperthyroidism and hyperthyroidism-associated clinical signs in cats.
Do not use in cats suffering from concurrent systemic diseases, such as severe primary liver disease or diabetes mellitus. Do not use in cats showing signs of auto-immune diseases and/or altered red or white blood cell counts, such as anaemia, neutropaenia or lymphopaenia.
Do not use in cats with platelet disorders (particularly thrombocytopaenia) or coagulopathies. Do not use in cats with hypersensitivity to mercaptoimidazoles (carbimazole or thiamazole (methimazole)). Please refer to section “Use during pregnancy or lactation”.
Thiamazole (methimazole), the active metabolite of carbimazole, inhibits thyroid hormone production and therefore cessation of treatment with carbimazole will result in a rapid (within 48 hours) return to pre-treatment thyroid hormone levels. Chronic administration is therefore necessary unless surgical or radiation-induced thyroidectomy is performed. A small proportion of cats with thyroid adenoma may fail to respond or have a poor response to treatment. Thyroid carcinoma is a rare cause of hyperthyroidism in the cat and medical management alone is not recommended in such cases as it is not curative.
Treatment should be adjusted according to the risk:benefit assessment for the individual case.Treatment of hyperthyroidism may result in a reduction in the glomerular filtration rate.This can lead to unmasking of pre-existent renal dysfunction. Treatment of hyperthyroidism may also induce an elevation of liver enzymes or a worsening of pre-existing hepatic disorders. Renal and liver function should therefore be monitored before and during treatment. Due to risk of leucopenia or haemolytic anaemia, haematology parameters should be monitored on a regular basis before and during treatment, preferably at each visit of the dose adjustment phase and maintenance phase (see Section "Amounts to be administered and administration route"). Any animal that suddenly appears unwell during therapy, particularly if they are febrile, should have a blood sample taken for routine haematology and biochemistry. Neutropenic animals (neutrophil counts <2.5 x 109/l) should be treated prophylactically with bactericidal antibiotics and supportive therapy. Doses above 20 mg have only been trialled in a small number of cats. Therefore, careful monitoring is recommended and the dose should be adjusted according to the risk:benefit assessment for the individual case.
Wash hands with soap and water after use and when handling litter used by treated animals. Do not handle this product if you are allergic to antithyroid products. Pregnant women should wear gloves when handling the product. Do not eat, drink or smoke while handling the tablet or used litter. In the case of accidental ingestion, seek medical advice immediately and show the package insert or the label to the physician. Carbimazole, as a prodrug of thiamazole (methimazole), may cause vomiting, epigastric distress, headache, fever, arthralgia, pruritus and pancytopaenia. Treatment is symptomatic. As carbimazole is a suspected human teratogen, women of child-bearing age should wear gloves when handling litter or vomit of treated cats.
Most frequent common adverse reactions encompass vomiting, diarrhoea, reduced appetite, loss of condition, lethargy, tachycardia, polydipsia, dehydration, and polyuria. Dermatological signs (pruritus, moist dermatitis, erythema, alopecia) have also been reported. These clinical signs are usually mild, adequately controlled by symptomatic therapy and do not require treatment discontinuation. However, if more severe clinical signs occur that do not respond to symptomatic therapy, the dose should be reduced or treatment stopped according to risk:benefit evaluation. In cases of serious adverse reactions, mortality, possibly due to the product, might occur if treatment is not discontinued. In some cases, signs of gastrointestinal bleeding such as bloody vomit, oral haemorrhage or dark feces can be observed. These signs should be considered as serious and require immediate action (dose reduction or treatment discontinuation). Weight loss, dyspnoea, aggressiveness, disorientation, ataxia or pyrexia have also been reported in rare cases. Treatment of hyperthyroidism may result in a reduction in the glomerular filtration rate. In severe cases, where azotaemia develops, temporary or permanent treatment discontinuation may be required. The treatment may induce increase of liver enzymes. Severe cases may require temporary or permanent treatment discontinuation. However, these elevations are usually reversible following drug discontinuation, although symptomatic therapy (nutritional and fluid support) may be required. Anaemia, increase or decrease in white blood cell count, neutrophilia, thrombocytopaenia, eosinophilia and/or lymphopaenia may also occur, in particular during the first 4-6 weeks of treatment. Treatment discontinuation may be required in case of persistent and marked disorder. In most of the cases, the abnormality will resolve spontaneously within 1 month after treatment discontinuation. Positive antinuclear antibody titres have also been reported. It appears that adverse reactions are reversible on cessation of treatment.
Laboratory studies in rats and mice have shown evidence of teratogenic and embryotoxic effects of thiamazole. The safety of the product was not assessed in pregnant or lactating cats. Furthermore, thiamazole crosses the placenta, distributes into milk and reaches approximately the same concentration as in maternal serum. Do not use in pregnant or lactating females.
Concomitant treatment with phenobarbital may reduce the clinical efficacy of carbimazole. The concomitant use of benzimidazole anthelmintics (fenbendazole or mebendazole) has been shown to reduce the hepatic oxidation of this therapeutic class and may therefore induce an increase of their circulating rates. Accordingly, co-administration of carbimazole with a benzimidazole is not recommended. Thiamazole may display immunomodulating properties. This should be taken into account when considering vaccination of the cat
For oral use only. Administration with food enhances bioavailability. The timing of treatment and its relation to feeding should be kept consistent from day to day. Do not break or crush Vidalta tablets as this will affect the sustained release property. The aim of treatment is to maintain total thyroxin concentrations (TT4) in the lower end of the reference range. Accordingly, the following dose recommendations for dosing during adjustment and maintenance phases are suggested. However dosing adjustment should be primarily based upon the clinical assessment of the individual cat. Monitoring of TT4, full haematology and liver and kidney parameters is advised at each recommended follow up visit (see sections "Special precautions for use" and "Adverse Reactions").
Adjustment phase The starting dose is a single daily oral administration of one tablet of 15 mg carbimazole per cat. Consideration could be given to a starting dose of Vidalta 10 mg daily where the TT4 concentration is only mildly increased, e.g. between 50 nmol/L and 100 nmol/L. With the recommended starting dose of one Vidalta 15 mg tablet once daily, total thyroxin concentration (TT4) may decrease to within the euthyroid range (TT4<50 nmol/L) shortly after treatment initiation. A dose adjustment may be required as early as 10 days of treatment. Dose adjustment should be also performed 3, 5 and 8 weeks after initiation of treatment, depending on both clinical and hormonal responses to treatment.
Maintenance phase Follow-up visits every 3 to 6 months are recommended. The dose should be adjusted individually based on clinical signs and total thyroxin concentration (TT4). It is advisable to check TT4 10-14 days after dose adjustment. The therapeutic dose of Vidalta ranges between 10 mg (one 10 mg tablet) and 25 mg (one 10 mg tablet and one 15 mg tablet) once daily. Some cats require doses of less than 10 mg carbimazole daily. Every other day dosing with 10 mg or 15 mg of carbimazole may be sufficient to control the disease. Dose increases should not be made in increments of greater than 5 mg. Doses above 20 mg have only been trialled in a small number of cats and should be used with caution.
In case of overdosage, adverse effects that may appear include, but are not limited to, weight loss, inappetence, vomiting, lethargy and less frequently signs of gastrointestinal bleeding such as haematemesis, oral haemorrhage, or haemorrhage of the intestinal tract. Coat and skin abnormalities (erythema, alopecia), as well as as haematological/biochemical changes (eosinophilia, lymphocytosis, neutropaenia, lymphopaenia, slight leucopaenia, agranulocytosis, thrombocytopaenia or haemolytic anaemia) may also appear. Hepatitis and nephritis have been reported. These adverse effects may become severe in case of chronic overdosing. In most cases, adverse effects are reversible upon treatment discontinuation and appropriate veterinary care. Total thyroxin concentrations (TT4) below the lower limit of the reference range may be observed during treatment although this is rarely linked to overt clinical signs. Decreasing the dose will lead to an increase of the TT4. Dose adjustment should not be made based on TT4 only (see Section “Amounts to be administered and Administration Route”). Please also refer to Section “Adverse Reactions”.
ATC Vet Code: QH 03 BB 01
Pharmacotherapeutic group: sulphur-containing imidazole derivatives.
Carbimazole is the prodrug of thiamazole (methimazole). Although carbimazole has inherent antithyroid activity, it is almost totally converted to thiamazole soon after its oral administration in vivo in humans and cats. Thiamazole results in dose-dependent inhibition of the thyroid peroxidase-catalysed reactions involved in thyroid hormone synthesis, including oxidation of iodide and iodination of tyrosyl residues in thyroglobulin, thereby inhibiting neosynthesis of thyroid hormones. Thiamazole also interferes with the coupling of iodotyrosines to iodothyronines via inhibition of thyroid peroxidase or by binding and altering the structure of thyroglobulin, this reaction being more sensitive to inhibition than the formation of iodotyrosines. The inhibitory action of thiamazole is reversible. Thiamazole does not inhibit the action of thyroid hormones already formed and present in the thyroid glands or bloodstream, or interfere with the effectiveness of administered exogenous thyroid hormone (iatrogenic hyperthyroidism). This explains why the length of the latency period until normalisation of serum concentrations of thyroxine and triiodothyronine, and thus to clinical improvement, differs between individuals.
Carbimazole is rapidly absorbed from the gastrointestinal tract after oral administration and hydrolysed in the gastrointestinal tract (or immediately after entering into the circulation) to the active metabolite thiamazole. The absolute bioavailability of thiamazole from carbimazole in Vidalta 15 mg tablets is 88%. Following oral administration of one tablet of Vidalta 10 mg to healthy fasted cats, maximum thiamazole concentrations are observed 3-4 hours after administration, with a mean peak concentration of thiamazole of 0.54-0.87 µg/ml. Following oral administration of one tablet of Vidalta 15 mg to healthy fasted cats, maximum thiamazole concentrations are observed 5-7 hours after administration, with a mean peak concentration of thiamazole of 0.72-1.13 µg/ml. For both strengths, the thiamazole concentration/time profile is devoid of pronounced peak and thiamazole persists in the circulation at least 20 and 24 hours for Vidalta 10 mg and Vidalta 15 mg, respectively. The presence of food in the gastrointestinal tract at the time of administration has been shown to increase the bioavailability of thiamazole. When tablets are administered with food, both Cmax and AUClast may be increased whereas tmax is not expected to change. No cumulative effects are observed upon repeated administration.The tissue distribution of mercaptoimidazoles has not been specifically studied in cats but has been fully described in rodents. Thiamazole is mainly concentrated in the thyroid and adrenal glands, and can be found to a lesser extent in the thymus, diaphragm, kidneys, brain, liver, colon, testes, small intestine, stomach and plasma. Mercaptoimidazoles have also been shown to cross the placental barrier. In rats, thiamazole is excreted mainly via the urine, and to a lesser extent in the faeces.
Hypromellose, Microcrystalline cellulose, Red ferric oxide (E 172), Silica colloidal anhydrous, Magnesium stearate and Talc.
Shelf life of the veterinary medicinal products as packaged for sale:
10 mg prolonged-release tablets: 18 months.
15 mg prolonged-release tablets: 24 months.
Do not store above 25°C. Store in the original container. Keep the container tightly closed to protect from moisture. Do not remove the desiccant.
High density polyethylene container of 30 or 100 tablets closed with polypropylene tamper-evident, child-resistant, screw cap bearing a desiccant. Cartons containing 1 or 6 containers. Not all pack sizes may be marketed.
Any unused veterinary medicinal product or waste materials derived from such veterinary medicinal product should be disposed of in accordance with local requirements.
21 December 2007.
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