an 11-year - old spayed female domestic shorthair cat with a history of hyperthyroidism treated with carbimazole for 7 months was presented for a check - up after a few episodes of vomiting .
the cat had been receiving prednisolone at 0.5 mg / kg po q12h for recent pancreatitis and concurrent inflammation of liver and small intestines confirmed by biopsies . clinical examination revealed pale mucous membranes with a capillary refill time of < 2 s. haematology showed severely decreased packed cell volume ( 16% ) , and increased prothrombin time ( 42 s ) , partial thromboplastin time ( > 120 s ) and fibrinogen serum concentration ( 3.5
morphological changes of thrombocytes in the absence of thrombocytopenia were also noted . in - saline agglutination test was positive .
feline leukaemia virus and feline immunodeficiency virus tests were negative . on the basis of these findings , immune - mediated anaemia secondary to chronic carbimazole administration
prednisolone was increased to 2 mg / kg po q24h and carbimazole tablets were stopped . despite close monitoring and intensive care ,
this report suggests that severe haemotoxicity may occur as a sequel of chronic carbimazole administration in cats .
routine bloodwork and accurate follow - up of cats under treatment with thyrotoxic therapy may be advisable , in order to detect haematological changes before lethal complications occur .
hyperthyroidism is one of the most common endocrine disease in cats , especially in middle - aged to older cats . owing to concurrent geriatric problems , which are likely to increase the risk of anaesthetic - related complications , medical treatment is often preferred over surgical thyroidectomy .
serious haematological side effects are a well - known complication for patients on thyrotoxic treatment , although only two cases of methimazole - induced haemotoxicity have been reported in cats .
we report a life - threatening haematological complication occurring in a cat after chronic carbimazole administration .
an 11-year - old spayed female domestic shorthair cat weighing 5.9 kg , with a history of hyperthyroidism treated with carbimazole for the past 7 months , was presented for a check - up after a few episodes of vomiting .
total thyroxine , haematology and biochemistry were monitored routinely every 3 months . since the beginning of the therapy ,
the treatment started on carbimazole 15 mg po q24h and the dosage was fixed accordingly with monitoring to reach a dose of 10 mg po q24h where the cat was stable .
the cat was also receiving prednisolone at 0.5 mg / kg po q12h for recent pancreatitis and concurrent inflammation of liver and small intestines , confirmed with biopsies . at presentation , the cat was alert and responsive .
its body condition score was 2/5 and the cat had gained 200  ; g in body weight during the previous month .
heart rate was 164 beats per minute , with no identifiable heart murmur and the lung sounds were clear .
blood was collected for a comprehensive panel and manual packed cell volume ( pcv ) .
g / l ; reference interval [ ri ] 6080 ) , mild hypoalbuminaemia ( 22  ; g / l ; ri 2546 ) and decreased creatinine serum concentration ( 69 mol / l ; ri 88177 ) .
serum total thyroxine was within normal limits for the species ( 45 nmol / l ; ri 1950  ; nmol / l ) but borderline for a cat on treatment with carbimazole .
reticulocyte count revealed a regenerative anaemia ( 0.17  ; 10/ml ) and on the blood smear red blood cells showed polychromasia and anisocytosis .
few lymphocytes appeared reactive with deeply basophilic cytoplasm and occasionally with abundant pale basophilic cytoplasm .
feline leukaemia virus ( felv ) and feline immunodeficiency virus ( fiv ) tests were negative ( idexx snap test ) .
a coagulative panel showed that prothrombin time ( 42 s ; ri 7.011.0 s ) , partial thromboplastin time ( > 120 s ; ri 13.020.0 s ) and fibrinogen serum concentration ( 3.5
abdominal ultrasound and t - fast were also normal and no pericardial , pleural or peritoneal effusion were found .
the liver appeared heterogeneous with no overt masses ; the spleen was homogenous and small .
the right kidney was 4.3 cm in length , the left one measured 3.7 cm and the architecture of both appeared normal .
based on these results , we could rule out the most common causes of immune - mediated anaemia and conclude that the haematological disorder was secondary to chronic carbimazole administration .
doxycycline was started at 5  ; mg / kg po q12h with the purpose of treating an undetected mycoplasma haemofelis infection .
omeprazole was also started at 1 mg / kg po q24h to prevent gastrointestinal ulceration due to the prednisolone immunosuppressive dose .
the possibility of a blood transfusion was mentioned to the owner , who declined the procedure owing to the potential for complications .
blood pressure was measured every 2 h , while pcv was monitored every 8 h. body temperature was maintained within normal ranges for the species by active warming . despite close monitoring and intensive care , the cat died the same evening of admission to the hospital .
differential diagnoses for immune - mediated anaemia in cats include infectious , neoplastic and chronic diseases , as well as drugs and toxins . in our case , the diagnostic investigations were suggestive of immune - mediated anaemia secondary to chronic carbimazole administration .
infectious diseases were excluded on the basis of the negative results for fiv and felv testing of serum .
furthermore , the cat was an indoor cat and had no possibility of contact with other cats .
there was no evidence of neoplastic disease , as corroborated by the ultrasonographic and radiographic findings , which failed to identify the presence of masses , organ enlargement or cavitary effusions .
a haematological disorder resulting from chronic disease can not be completely ruled out . a chronic pancreatitis , with concurrent inflammation of liver and small intestine ,
the coagulation abnormalities detected in this cat , namely the increased prothrombin time , partial thromboplastin time and fibrinogen serum concentration , together with the immunomediated origin of the anaemia , as confirmed by the positive in - saline agglutination test , seem to indicate the carbimazole toxicity as the most likely cause .
similar cases of severe anaemia caused by methimazole were treated by discontinuing the treatment , with no re - challenge with antithyroid drugs . alongside this
, it has been recommended to administer prednisolone ( 12 mg / kg po q1224h ) and doxycycline ( 5 mg / kg po q12h ) . in order to prevent gastric ulceration due to a high dose of prednisolone ,
proton pump inhibitors ( omeprazole 0.51.0 mg / kg po q24h ) must be used .
h2-receptor antagonists ( ranitidine 1 mg / kg po q12h ) can also be used to decrease pepsin and gastric acid secretions and so have a secondary efficacy .
clinical side effects typically associated with chronic carbimazole therapy include anorexia , vomiting and lethargy , but these signs are usually mild and transient , and similar to those reported with methimazole .
more serious side effects are reported for methimazole , such as hepatopathy , bleeding diathesis ( prolonged proteins induced by vitamin k absence or antagonists [ pivka ] clotting time ) and marked thrombocytopenia .
anaemia , including aplastic anaemia , was reported by chapman et al , after 3 years of treatment , and also by weiss in 2006 .
it is also of note that there may be synergistic side effects with the combination of other drugs , even if the severity is unknown .
when used concurrently , there may be a chance that carbimazole competes with this other drug for protein binding and so causes adverse side effects .
carbimazole is a well - studied thyrotoxic drug which is considered to have fewer life - threatening side effects than methimazole .
although carbimazole may be better tolerated in cats than methimazole , the potential for serious adverse reactions still exists . in order to detect them ,
mooney et al recommended carrying out a complete blood count every 2 weeks , at least for the first 3 months of therapy , when these reactions are most likely to occur .
owing to the rapid course of events , as well as to the severity of the condition at presentation , the cat died on the same night of admission to the hospital .
a closer follow - up of the cat during carbimazole treatment could have allowed for an earlier detection of the haematological changes , in order to undertake preventive measures before lethal complications occurred .
life - threatening side effects , occasionally reported with methimazole in cats , may occur also with carbimazole .
routine bloodwork and accurate follow - up of cats under treatment with thyrotoxic therapy may be advisable , in order to detect haematological changes before lethal complications occur .
 case summaryan 11-year - old spayed female domestic shorthair cat with a history of hyperthyroidism treated with carbimazole for 7 months was presented for a check - up after a few episodes of vomiting . 
 the cat had been receiving prednisolone at 0.5 mg / kg po q12h for recent pancreatitis and concurrent inflammation of liver and small intestines confirmed by biopsies . clinical examination revealed pale mucous membranes with a capillary refill time of < 2 s. haematology showed severely decreased packed cell volume ( 16% ) , and increased prothrombin time ( 42 s ) , partial thromboplastin time ( > 120 s ) and fibrinogen serum concentration ( 3.5 
 g / l ) . 
 morphological changes of thrombocytes in the absence of thrombocytopenia were also noted . in - saline agglutination test was positive . 
 abdominal radiographic and ultrasonographic examinations excluded the presence of organ abnormalities and peritoneal effusion . 
 blood biochemistry was unremarkable . 
 feline leukaemia virus and feline immunodeficiency virus tests were negative . on the basis of these findings , immune - mediated anaemia secondary to chronic carbimazole administration 
 was suspected . 
 prednisolone was increased to 2 mg / kg po q24h and carbimazole tablets were stopped . despite close monitoring and intensive care , 
 the cat died the same evening of admission to the hospital.relevance and novel informationthis report suggests that severe haemotoxicity may occur as a sequel of chronic carbimazole administration in cats . 
 routine bloodwork and accurate follow - up of cats under treatment with thyrotoxic therapy may be advisable , in order to detect haematological changes before lethal complications occur . 
Case summary
Relevance and novel information
Introduction
Case description
Discussion
Conclusions