Effects of methimazole on renal function in cats with hyperthyroidism

Abstract

The purpose of this study was to investigate the effects of methimazole on renal function in cats with hyperthyroidism. Twelve cats with naturally occurring hyperthyroidism and 10 clinically normal (i.e., control) cats were included in this study. All cats initially were evaluated with a history, physical examination, complete blood count, serum biochemistry profile, basal serum total thyroxine concentration, complete urinalysis, and urine bacterial culture. Glomerular filtration rate (GFR) was estimated by a plasma iohexol clearance (PIC) test. After initial evaluation, hyperthyroid cats were treated with methimazole until euthyroidism was achieved. Both groups of cats were then reevaluated by repeating the initial tests four to six weeks later. The mean (+/-standard deviation) pretreatment estimated GFR for the hyperthyroid cats was significantly higher (3.83+/-1.82 ml/kg per min) than that of the control cats (1.83+/-0.56 ml/kg per min). Control of the hyperthyroidism resulted in a significantly decreased mean GFR of 2.02+/-0.81 ml/kg per minute when compared to pretreatment values. In the hyperthyroid group, the mean increases in serum urea nitrogen (SUN) and creatinine concentrations and the mean decrease in the urine specific gravity after treatment were not statistically significant when compared to pretreatment values. Two of the 12 hyperthyroid cats developed abnormally high serum creatinine concentrations following treatment. These results provide evidence that cats with hyperthyroidism have increased GFR compared to normal cats, and that treatment of feline hyperthyroidism with methimazole results in decreased GFR.

Evaluation of the effects of nephrotomy on renal function in clinically normal cats

“…No standardized anesthetic protocols exist for estimating GFR in cats. Previous studies of renal function in cats involved nonanethestized animals 23,25,[31][32][33] or animals restrained by use of thiopental sodium, 34 pentobarbital sodium, 35,36 ketamine hydrochloride, 22,37 halothane, 20 tiletamine hydrochloride and zolazepam hydrochloride (telazole), 38 or medetomidine hydrochloride and butorphanol tartrate administration. 39 In our study, the first scintigraphic evaluation to estimate preoperative GFR was performed on cats anesthetized by use of isoflurane as a single agent to facilitate catheter placements, collection of samples, and restraint for scintigraphy.…”

American Association of Feline Practitioners: Senior Care Guidelines

“…Note that: -Hypertension may persist or even develop after treatment. 21,64,65 -Hypertension secondary to hyperthyroidism alone may self-correct when a euthyroid state is achieved. 18 -Renal function should be monitored.…”

Feline hyperthyroidism: diagnosis and treatment

“…Approximately 20-25% of feline hyperthyroidism cases without known chronic kidney disease will develop azotaemia, regardless of therapeutic modality, as a result of decline of glomerular filtration rate (Graves, 2010). Increases in serum creatinine concentrations occur in 15-50% of cats after treatment (Adams et al, 1997;Becker et al, 2000,;Slater et al, 2001;Williams et al, 2010). Evaluation of various parametres (urine specific gravity, blood urea nitrogen, creatinine concentration) before treatment are not useful in predicting potential development of post-treatment azotaemia (Riensce et al, 2008).…”