Medical Management and Monitoring of the Hyperthyroid Cat, Survey of UK General Practitioners

Higgs P., Murray J. and Hibbert A.

Conference Proceedings, (2013). British Small Animal Veterinary Congress: p.1-2

Feline hyperthyroidism is commonly managed with anti­thyroid medication, however, consensus regarding monitoring of treated cats is currently lacking. This study aimed to evaluate how veterinarians monitor for drug efficacy, adverse drug reactions and co­morbid diseases including chronic kidney disease (CKD) and hypertension. General practitioners working in practices that were registered with the RCVS as having feline patients were contacted by email or post, and adverts were placed in veterinary media. During a six week period, beginning 21st August 2012, 603 veterinarians completed an online survey comprising 34 questions covering demographics, general approach to management, radioiodine, medical and surgical therapy.

Regarding the formulation of oral therapy, 51.6% preferred sustained release carbimazole, 40.5% methimazole whilst 6.5% had no specific preference. Neomercazole® (standard carbimazole) was preferred by 1.5% but is unlicensed for cats. Regarding formulation of a monitoring protocol, 37.8% followed practice protocol, 37.1% designed their protocol according to owner desires and 22.7% followed datasheet guidelines.
Concerning target T4 levels, 48.4% aimed for the lower half of the reference interval (RI), 32.3% anywhere within RI, 13.1% within the top half of RI, and 0.5% above the RI, whilst 3.4% evaluated efficacy by physical assessment only. Chi­squared analysis revealed that, in the presence of CKD, respondents were more likely (P < 0.001) to target T4 levels within the upper half of (40.3%), or above (9.8%) RI, when compared with targets for routine cases. Assessment for unmasking of CKD after initiating treatment was not routinely performed; 29% of respondents did not evaluate renal parameters (urea, creatinine), 53.1% did not perform urinalysis. Once stabilised, body weight was the most commonly monitored parameter, with greater than 95% of veterinarians assessing this at least every six months. Serum thyroxine (T4) was evaluated by 80.8%, renal parameters by 71.2%, systolic blood pressure by 40.4% and urinalysis by 36.9% at least every six months. Adverse reactions were described by 67.0% of respondents within the previous six months. Vomiting (69.1%), anorexia (47.0%) and facial pruritus (44.8%) were most common. Anaemia, thrombocytopenia or neutropenia, were described by 28.4% of respondents, although only 47.3% routinely assessed haematology during the period of stabilisation. Current monitoring strategies may result in CKD and hypertension remaining undetected and inadequate suppression of T4 levels in cats with concurrent CKD. The variability in monitoring practices may also result in delayed recognition of potentially significant haematological abnormalities.