Effects of the angiotensin converting enzyme inhibitor benazepril in cats with induced renal insufficiency

Bridging the gap-Rethinking the role of the adrenal gland in chronic kidney disease from the feline perspective

Chronic kidney disease (CKD) is the most common metabolic disease in domestic cats. Unlike humans and dogs, CKD in cats seems to have a highly complex and multifactorial etiology. Despite great effort being poured into research trying to elucidate possible pathways for the pathogenesis of CKD, there is still a lack of understanding regarding its initiating and progression factors. There is also a lack of therapeutic options for these patients, with most treatment plans relying on a low-phosphate diet, dietary protein modification and medical management of complications (e.g. hypertension) as they arise. In this review, we propose the hypothalamic-pituitary-adrenal (HPA) axis plays a central role in the development, pathophysiology and progression of feline chronic kidney disease. The adrenal glands and the hormones they secrete, in particular, may act as lynchpins in chronic kidney disease, mediating virtually every aspect of the disease: from the establishment of fibrosis and kidney damage to the development of hypertension and a pro-inflammatory status. By compiling the available research regarding the influence of adrenal hormones and the HPA axis, we hope to highlight possible future areas of scientific interest regarding feline CKD as well as possible aspects in which the cat may act as a model for research in human medicine.

Evolving value and validity of animal models in veterinary therapeutic research: Impact of scientific progress

In veterinary medicine, experimental in vivo animal models have long been integral to advancing our understanding of disease mechanisms and assessing the safety and efficacy of potential therapies. However, the value and validity of these models warrants reassessment in light of emerging scientific evidence, evolving standards in animal welfare, and the development of alternative methodologies. Such a reassessment is essential for maintaining ethical scientific practices and ensuring that research approaches remain both relevant and justifiable, especially as our awareness of animal pain, sentience, and consciousness deepens. While interspecies extrapolation of findings from these models poses challenges when applied to human medicine, what about cases where an animal species serves as both the experimental subject and the intended veterinary patient? Additionally, what alternative tools are potentially available to replace in vivo studies in these contexts? This commentary explores how veterinary research may improve efforts to meet the principles of the 3R's by integrating alternative in vitro and in silico models early in the investigative process and utilizing specialized tools within the target veterinary population during clinical trials.

The renin-angiotensin-aldosterone system in kidney diseases of cats and dogs

The renin-angiotensin-aldosterone system (RAAS) has a well-established key pathophysiologic role in kidney diseases, and pharmacotherapy targeting this system is a mainstay of treatment of affected human beings, cats, and dogs. Several studies have evaluated the circulating RAAS in animals with spontaneous or experimentally induced kidney diseases. Evidence supporting the activation of this system has been demonstrated in some - but not all - studies and individuals, and the interindividual variability in circulating RAAS markers is high. Advances over the last few decades have expanded our understanding of the system, which now includes the existence of a counterbalancing "alternative" RAAS and tissular renin-angiotensin systems (RASs), the latter regulated independently of the circulating endocrine RAAS. The local RAS in the kidney, termed the intrarenal RAS, is currently recognized as an important regulator of kidney function and mediator of kidney disease. In general, information on the intrarenal RAS is lacking in cats and dogs with kidney diseases; however, existing limited data suggest its activation. Despite the inconsistent evidence for circulating RAAS activation in chronic kidney diseases, RAAS inhibitors have proven effective for the treatment of its common comorbidities, systemic arterial hypertension and renal proteinuria, in both cats and dogs. Further research of the circulating RAAS, the intrarenal RAS, and the interplay between these systems in the context of kidney diseases in companion animals might contribute to the development or refinement of future treatment strategies.

Sodium glucose transporter 2 inhibitors: Will these drugs benefit non-diabetic veterinary patients with cardiac and kidney diseases?

Sodium glucose transporter type 2 (SGLT2) inhibitors have been introduced into human medicine where their beneficial effects go beyond the expected improvement in blood glucose control. These drugs appear to prevent progression of both cardiovascular and kidney diseases, not only in diabetic but also in non-diabetic human patients. As these drugs have received conditional approval for use in diabetic cats and are being used in other veterinary species, the intriguing question as to whether they will have similar cardioprotective and nephroprotective effects in dogs and cats is being asked. The primary mechanism(s) by which SGLT2 inhibitors are cardio- and nephroprotective remain to be fully characterized. This paper reviews these suggested mechanisms in the context of the pathophysiology of progressive cardiovascular and kidney diseases in dogs and cats with the goal of predicting which categories of non-diabetic veterinary patients these drugs might be of most benefit.

Use of amlodipine in the treatment of cats with systemic hypertension in Japan

An increase in systemic blood pressure causes bleeding and ischemia owing to peripheral vascular breakdown, leading to various forms of organ damage. The brain, eyes, kidneys, and cardiovascular system are known target organs for hypertension. To our knowledge, no reports in Japan describe, in detail, the types of antihypertensive drugs used to treat hypertension in cats or its underlying causes. Therefore, we aimed to investigate the use of antihypertensive drugs in domestic cats with hypertension in Japan, the causes of hypertension, and the vital prognosis of these patients. In the present survey, we found that amlodipine was used alone (60/80 cats) or concomitantly (20/80 cats) in all cat patients with hypertension in Japan. We also determined that blood pressure measurements were not yet routinely performed on cats at veterinary clinics in Japan. Furthermore, we have new information suggesting that amlodipine administration in cats with hypertension, which lowers systolic arterial pressure levels to within the normal range (<140 mmHg), may have a negative impact on their survival. Routine blood pressure measurements for cats during their regular health checkups can help identify hypertension, and proper interpretation of blood pressure readings can facilitate suitable treatment measures.

Feline comorbidities: The intermingled relationship between chronic kidney disease and hypertension

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is a highly prevalent disorder of senior cats. CKD is frequently diagnosed in association with hypertension, and the two conditions have an intermingled cause-and-effect relationship. Hypertensive target organ damage (TOD) to the eye, brain, heart and kidney significantly impacts the welfare of cats suffering from this comorbidity. Hypertension also drives proteinuria, which is an independent risk factor for progression and mortality in cats with CKD. Blood pressure monitoring and institution of effective antihypertensive treatment, where indicated, is therefore crucial in effective management of the feline CKD patient. Current guidelines recommend a target systolic blood pressure of <160 mmHg to minimise risk of TOD. Both amlodipine besylate and telmisartan are effective antihypertensive agents for use in these patients.

CLINICAL CHALLENGES

Clinical signs of hypertension may not be apparent to owners of affected cats until severe hypertensive TOD is present. Despite this, blood pressure monitoring in cats with CKD is still infrequently performed, and hypertension likely remains underdiagnosed in this population.

EVIDENCE BASE

This review is based upon evaluation of the currently available published literature, including relevant consensus statements. There is a large body of evidence supporting the association between hypertension and CKD in cats. However, significant aspects, such as the mechanisms behind this association, and effect of hypertension and antihypertensive treatment on mortality and progression of CKD, remain unclear. Further research is therefore required in order to improve understanding of these conditions.

Ocular fundus abnormalities in cats affected by systemic hypertension: Prevalence, characterization, and outcome of treatment

OBJECTIVES

To determine the prevalence of ocular fundus abnormalities in cats with a diagnosis of systemic hypertension, to characterize the abnormalities observed, and to evaluate ophthalmoscopic evolution during treatment with amlodipine besylate.

ANIMALS STUDIED

Cats diagnosed as affected by SHP in a 2-year period.

PROCEDURES

Systemic hypertension was assessed by oscillometric blood pressure measurement, and its etiology was also established. All the cats received an ophthalmic examination, and ocular lesions were classified with a score from 0 (no abnormalities) to 4 (severe abnormalities). All cats received amlodipine besylate by mouth, and those that showed fundus abnormalities were regularly rechecked from 7 to 365 days after diagnosis. Data were statistically analyzed to compare P_sys and P_dia with all the variables and to correlate P_sys and P_dia with the fundus score.

RESULTS

A total of 225 cats were enrolled in the study, and the prevalence of fundus abnormalities was 58.6% (21.2%: grade 1; 18.2%: grade 2; 36.4%: grade 3; and 24.2%: grade 4). Systemic hypertension was diagnosed concurrently with chronic renal failure (60.4%), hyperthyroidism (28.9%), both chronic renal failure and hyperthyroidism (7.6%), and hypertrophic myocardiopathy (3.1%). A significant effect of P_sys values on the fundus score was detected. Amlodipine therapy improved fundus abnormalities in 50% of cases at the 21-day follow-up.

CONCLUSIONS

This study showed that fundus abnormalities are common in hypertensive cats at the time of the systemic diagnosis, and most of the abnormalities are moderate to severe. Treatment with amlodipine appeared to improve ophthalmic lesions over time.

Aldosterone and the mineralocorticoid receptor in renal injury: A potential therapeutic target in feline chronic kidney disease

There is a growing body of experimental and clinical evidence supporting mineralocorticoid receptor (MR) activation as a powerful mediator of renal damage in laboratory animals and humans. Multiple pathophysiological mechanisms are proposed, with the strongest evidence supporting aldosterone-induced vasculopathy, exacerbation of oxidative stress and inflammation, and increased growth factor signalling promoting fibroblast proliferation and deranged extracellular matrix homeostasis. Further involvement of the MR is supported by extensive animal model experiments where MR antagonists (such as spironolactone and eplerenone) abrogate renal injury, including ischaemia-induced damage. Additionally, clinical trials have shown MR antagonists to be beneficial in human chronic kidney disease (CKD) in terms of reducing proteinuria and cardiovascular events, though current studies have not evaluated primary end points which allow conclusions to made about whether MR antagonists reduce mortality or slow CKD progression. Although differences between human and feline CKD exist, feline CKD shares many characteristics with human disease including tubulointerstitial fibrosis. This review evaluates the evidence for the role of the MR in renal injury and summarizes the literature concerning aldosterone in feline CKD. MR antagonists may represent a promising therapeutic strategy in feline CKD.

The Multicomponent, Multitarget Therapy SUC in Cats with Chronic Kidney Disease: A Multicenter, Prospective, Observational, Nonrandomized Cohort Study

BACKGROUND

We compared the natural multicomponent, multitarget therapy SUC (Solidago compositum ad us. vet., Ubichinon compositum and Coenzyme compositum, Heel GmbH, Baden-Baden, Germany) to the well-known angiotensin-converting enzyme inhibitor benazepril in a prospective, observational, nonrandomized, two-arm cohort study of cats with chronic kidney disease (CKD). The objective was to assess the tolerability and the effectiveness of SUC in cats with CKD.

MATERIAL AND METHODS

One hundred thirty-six cats were screened for CKD, and 70 cats were eligible for the study. Thirty-three cats were assigned to the SUC treatment, and 35 cats received benazepril. All cats were diagnosed with CKD. The follow-up period was 168 days. Response was assessed as an improved or stable serum creatinine from baseline to the end of the study. Additionally, a clinical summary score, as measure of quality of life, was evaluated.

RESULTS

Serum creatinine remained close to baseline in both study groups with slightly improved values in the SUC group. The clinical summary score improved significantly in the SUC group on days 3, 7, 28, 56 and 112, but not on day 168.

CONCLUSIONS

Within the limitations of the study, the results carry implications for the usefulness of SUC as an interesting new treatment option for feline CKD. The results indicate that SUC might be more effective if given at least twice weekly.

Evaluation of benazepril in cats with heart disease in a prospective, randomized, blinded, placebo-controlled clinical trial

Background

Heart disease is an important cause of morbidity and mortality in cats, but there is limited evidence of the benefit of any medication.

Hypothesis

The angiotensin‐converting enzyme inhibitor benazepril would delay the time to treatment failure in cats with heart disease of various etiologies.

Animals

One hundred fifty‐one client‐owned cats.

Methods

Cats with heart disease, confirmed by echocardiography, with or without clinical signs of congestive heart failure, were recruited between 2002 and 2005 and randomized to benazepril or placebo in a prospective, multicenter, parallel‐group, blinded clinical trial. Benazepril (0.5‐1.0 mg/kg) or placebo was administered PO once daily for up to 2 years. The primary endpoint was treatment failure. Analyses were conducted separately for all‐cause treatment failure (main analysis) and heart disease‐related treatment failure (supportive analysis).

Results

No benefit of benazepril versus placebo was detected for time to all‐cause treatment failure (P = .42) or time to treatment failure related to heart disease (P = .21). Hazard ratios (95% confidence interval [CI]) from multivariate analysis for benazepril compared with placebo were 1.00 (0.57‐1.74) for all‐cause failure, and 0.99 (0.50‐1.94) for forward selection and 0.93 (0.48‐1.81) for bidirectional selection models for heart disease‐related failure. There were no significant differences between groups over time after administration of the test articles in left atrium diameter, left ventricle wall thickness, quality of life scores, adverse events, or plasma biochemistry or hematology variables.

Conclusions and Clinical Relevance

Benazepril was tolerated well in cats with heart disease, but no evidence of benefit was detected.

Safety and efficacy of orally administered telmisartan for the treatment of systemic hypertension in cats: Results of a double-blind, placebo-controlled, randomized clinical trial

BACKGROUND

Information regarding the efficacy of telmisartan for feline systemic arterial hypertension is limited.

OBJECTIVES

To evaluate the safety and efficacy of PO administered telmisartan solution in hypertensive cats.

ANIMALS

Client-owned cats with indirect systolic arterial blood pressure (SBP) of 160-200 mm Hg, based on multiple measurements.

METHODS

This multicenter trial consisted a 28-day, prospective, randomized, double-blind, placebo-controlled, parallel group, efficacy phase and a 154-day extended-use telmisartan phase. Hypertensive cats were randomly assigned to receive 1.5 mg telmisartan/kg PO q12h for 14 days, followed by 2 mg telmisartan/kg PO q24h, or equivalent volume of placebo. Systolic blood pressure was measured on days 0, 14, and 28. Change in SBP compared to baseline was calculated for days 14 and 28. Telmisartan efficacy was defined as significant decrease in SBP at day 14 compared to placebo and a clinically relevant (>20 mm Hg) decrease in SBP at day 28.

RESULTS

Two-hundred twenty-one cats were included. On day 14, least squares mean (95% confidence interval) SBP decrease was significantly larger in telmisartan-treated (-23.3 mm Hg [-28.2 to -18.3]) versus placebo-treated (-7.5 mm Hg [-13.6 to -1.5]) cats (P = .0005). On day 28, telmisartan treatment resulted in a clinically relevant SBP decrease (-23.9 mm Hg [-27.8 to -20.0]), whereas placebo did not (-11.6 mm Hg [-17.4 to -5.9 mm Hg]). The decrease in SBP persisted over the 6-month trial in telmisartan-treated cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

Telmisartan significantly decreased SBP to a clinically relevant extent and was well tolerated in hypertensive cats.

Efficacy of long-term oral telmisartan treatment in cats with hypertension: Results of a prospective European clinical trial

Background

Efficacy of telmisartan in treating hypertension (HT) in cats has not been largely investigated.

Objective

Telmisartan oral solution effectively controls systolic arterial blood pressure (SABP) in hypertensive cats.

Animals

Two‐hundred eighty‐five client‐owned cats with systemic HT.

Methods

Prospective, multicenter, placebo‐controlled, randomized, double‐blinded study. Hypertensive cats diagnosed with SABP ≥160 mmHg and ≤200 mmHg without target‐organ‐damage were randomized (2 : 1 ratio) to receive 2 mg/kg telmisartan or placebo q24 PO. A 28‐day efficacy phase was followed by a 120‐day extended use phase. Efficacy was defined as significant difference in mean SABP reduction between telmisartan and placebo on Day 14 and group mean reduction in SABP of > 20 mmHg by telmisartan on Day 28 compared to baseline.

Results

Two‐hundred fifty‐two cats completed the efficacy and 144 cats the extended use phases. Mean SABP reduction at Day 14 differed significantly between groups (P < .001). Telmisartan reduced baseline SABP of 179 mmHg by 19.2 (95% confidence interval [CI]: 15.92‐22.52) and 24.6 (95% CI: 21.11‐28.14) mmHg at Days 14 and 28. The placebo group baseline SABP of 177 mmHg was reduced by 9.0 (95% CI: 5.30‐12.80) and 11.4 (95% CI: 7.94‐14.95) mmHg, respectively. Of note, 52% of telmisartan‐treated cats had SABP <150 mmHg at Day 28. Mean SABP reduction by telmisartan in severe (≥180 mmHg) and moderate HT (160‐179 mmHg) was comparable and persistent over time.

Conclusions and Clinical Importance

Telmisartan solution (PO) was effective in reducing SABP in hypertensive cats with SABP ≥160 mmHg and ≤200 mmHg.

ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats

An update to the 2007 American College of Veterinary Internal Medicine (ACVIM) consensus statement on the identification, evaluation, and management of systemic hypertension in dogs and cats was presented at the 2017 ACVIM Forum in National Harbor, MD. The updated consensus statement is presented here. The consensus statement aims to provide guidance on appropriate diagnosis and treatment of hypertension in dogs and cats.

Safety of Benazepril in 400 Azotemic and 110 Non-Azotemic Client-Owned Cats (2001-2012)

This retrospective study examined cats after initiation of benazepril therapy to determine the frequency of systemic hypotension or elevations in serum creatinine and/or potassium. Medical records review identified azotemic and non-azotemic cats prescribed benazepril. Blood pressure was recorded at the first available time after initiation of therapy. No cats experienced documented systolic systemic hypotension (<90 mmHg). Serum creatinine, and potassium when available, were recorded at baseline and in time windows after initiation of treatment: 1-30 days and 31-60 days. Blood chemistry results were screened for hyperkalemia (≥6.0 mEq/L). During the first 2 mo after starting benazepril therapy, there was a low incidence (3.7%) and clinically insignificant magnitude of hyperkalemia. Serum creatinine increases of greater than 30% from baseline were noted. This change was found in 11.0% of cats during the first 30 days of therapy and in 13.7% of cats from days 31-60 after initiation of therapy. The long-term survival of the cats that had >30% increases in creatinine from baseline was not statistically different from the survival of those that did not experience these increases, which suggests this finding may not be a reason to discontinue therapy. Benazepril appeared safe in a heterogeneous population of cats.

Pharmacodynamics of alacepril in healthy cats

Objectives The aims of this study were to investigate the pharmacodynamics of alacepril and to determine the appropriate dose for clinical usage in cats. Methods Six experimental cats were used. Each cat received alacepril orally at a single dose of 1 mg/kg, 2 mg/kg and 3 mg/kg. Blood samples were collected before administration and at 2, 4, 6, 8, 12, 24, 36, 48 and 72 h after administration to measure serum angiotensin converting enzyme (ACE) activity. Systolic blood pressure was also measured at the same time point. Results Dose-dependent inhibition of ACE activity was observed. Doses of 2 mg/kg and 3 mg/kg alacepril were considered to effectively inhibit ACE activity. There were no significant differences in systolic blood pressue among groups at any time point. Conclusions and relevance Alacepril 2-3 mg/kg q24h may be an appropriate dosage for clinical use in cats.

ISFM Consensus Guidelines on the Diagnosis and Management of Hypertension in Cats

Practical relevance: Feline hypertension is a common disease in older cats that is frequently diagnosed in association with other diseases such as chronic kidney disease and hyperthyroidism (so-called secondary hypertension), although some cases of apparent primary hypertension are also reported. The clinical consequences of hypertension can be severe, related to 'target organ damage' (eye, heart and vasculature, brain and kidneys), and early diagnosis followed by appropriate therapeutic management should help reduce the morbidity associated with this condition. Clinical challenges: Despite being a common disease, routine blood pressure (BP) monitoring is generally performed infrequently, probably leading to underdiagnosis of feline hypertension in clinical practice. There is a need to: (i) ensure BP is measured as accurately as possible with a reproducible technique; (ii) identify and monitor patients at risk of developing hypertension; (iii) establish appropriate criteria for therapeutic intervention; and (iv) establish appropriate therapeutic targets. Based on current data, amlodipine besylate is the treatment of choice to manage feline hypertension and is effective in the majority of cats, but the dose needed to successfully manage hypertension varies between individuals. Some cats require long-term adjuvant therapy and, occasionally, additional therapy is necessary for emergency management of hypertensive crises. Evidence base: These Guidelines from the International Society of Feline Medicine (ISFM) are based on a comprehensive review of the currently available literature, and are aimed at providing practical recommendations to address the challenges of feline hypertension for veterinarians. There are many areas where more data is required which, in the future, will serve to confirm or modify some of the recommendations in these Guidelines.

Current Understanding of the Pathogenesis of Progressive Chronic Kidney Disease in Cats

In cats with chronic kidney disease (CKD), the most common histopathologic finding is tubulointerstitial inflammation and fibrosis. However, these changes reflect a nonspecific response of the kidney to any inciting injury. The risk of developing CKD is likely to reflect the composite effects of genetic predisposition, aging, and environmental and individual factors that affect renal function over the course of a cat's life. However, there is still little information available to determine exactly which individual risk factors predispose a cat to develop CKD. Although many cats diagnosed with CKD have stable disease for years, some cats show overtly progressive disease.

Effect of benazepril, robenacoxib and their combination on glomerular filtration rate in cats

Background

Combined use of angiotensin-converting enzyme inhibitors and nonsteroidal anti-inflammatory drugs may induce acute kidney injury in humans, especially when combined with diuretics. The objective of this investigation was to evaluate the effects of benazepril, robenacoxib and their combination in healthy cats.

In each of two studies (study 1 followed by study 2), 32 healthy cats were randomised to one of four groups (n = 4 male and 4 female cats per group) in a parallel-group design. The groups received orally once daily for 7 days either placebo (control group), benazepril, robenacoxib or benazepril plus robenacoxib. In study 2, all groups received in addition 0.5 mg/kg furosemide twice daily by subcutaneous injection for 7 days.

Results

Benazepril, robenacoxib and their combination were well tolerated as evidenced from lack of clinical signs and no negative effects on body weight, feed consumption and clinical chemistry, haematology and urinalysis variables.

The primary endpoint of the study was the glomerular filtration rate (GFR), which was estimated from the plasma clearance of iohexol. In the absence of furosemide, GFR was significantly higher in cats receiving the combination of benazepril plus robenacoxib compared to the other three groups, and was also significantly higher in females receiving only benazepril compared to the control.

Administration of furosemide induced diuresis, reduced GFR and activated the renin-aldosterone-angiotensin system, evidenced from increased plasma renin activity and plasma aldosterone concentrations. Compared to the control group in cats treated with furosemide, GFR was increased by benazepril (females only) but decreased by robenacoxib (males only). Benazepril, robenacoxib and their combination significantly inhibited the increase in plasma aldosterone induced by furosemide.

Conclusions

The combination of benazepril and robenacoxib was well tolerated and either increased or had a neutral effect on GFR in healthy cats without or with concomitant furosemide. The combination of benazepril and robenacoxib reduced plasma aldosterone concentrations increased by furosemide. It is recommended to test the efficacy and safety of the combined use of benazepril and robenacoxib in cats with clinical disease, notably proteinuric chronic kidney disease.

Effect of benazepril and robenacoxib and their combination on glomerular filtration rate in dogs

Combined use of angiotensin-converting enzyme inhibitors and nonsteroidal anti-inflammatory drugs may induce acute kidney injury, especially when combined with diuretics. The objective of this investigation was to evaluate the effect of benazepril, robenacoxib and their combination in healthy dogs. In each of two studies (studies 1 and 2), 32 beagle dogs were randomized into one of four groups in a parallel-group design. Groups received once-daily oral treatment for 7 days with placebo, benazepril, robenacoxib or benazepril plus robenacoxib. In study 2, all dogs received additionally 2 mg/kg furosemide orally twice daily. The primary endpoint was the glomerular filtration rate (GFR) estimated from the plasma clearance of iohexol. Secondary endpoints included standard clinical monitoring and, in study 2, plasma renin activity, urine volume, specific gravity and aldosterone concentration and water intake. Administration of furosemide induced diuresis, reduced GFR and activated the renin-aldosterone-angiotensin system. Benazepril and robenacoxib, administered alone or in combination, were tolerated well, did not decrease GFR with or without co-administration of furosemide and significantly reduced urinary aldosterone concentrations. No increased risk of acute kidney injury was identified with the combination of benazepril and robenacoxib in healthy dogs. Different effects might occur in dogs with heart or renal disease.

Attenuation of the pressor response to exogenous angiotensin by angiotensin receptor blockers and benazepril hydrochloride in clinically normal cats

OBJECTIVE

To compare the attenuation of the angiotensin I-induced blood pressure response by once-daily oral administration of various doses of angiotensin receptor blockers (irbesartan, telmisartan, and losartan), benazepril hydrochloride, or lactose monohydrate (placebo) for 8 days in clinically normal cats.

ANIMALS

6 healthy cats (approx 17 months old) with surgically implanted arterial telemetric blood pressure-measuring catheters.

PROCEDURES

Cats were administered orally the placebo or each of the drug treatments (benazepril [2.5 mg/cat], irbesartan [6 and 10 mg/kg], telmisartan [0.5, 1, and 3 mg/kg], and losartan [2.5 mg/kg]) once daily for 8 days in a crossover study. Approximately 90 minutes after capsule administration on day 8, each cat was anesthetized and arterial blood pressure measurements were recorded before and after IV administration of each of 4 boluses of angiotensin I (20, 100, 500, and 1,000 ng/kg). This protocol was repeated 24 hours after benazepril treatment and telmisartan (3 mg/kg) treatment. Differences in the angiotensin I-induced change in systolic arterial blood pressure (ΔSBP) among treatments were determined.

RESULTS

At 90 minutes after capsule administration, only losartan did not significantly reduce ΔSBP in response to the 3 higher angiotensin doses, compared with placebo. Among drug treatments, telmisartan (3 mg/kg dosage) attenuated ΔSBP to a significantly greater degree than benazepril and all other treatments. At 24 hours, telmisartan was more effective than benazepril (mean ± SEM ΔSBP, 15.7 ± 1.9 mm Hg vs 55.9 ± 12.42 mm Hg, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that telmisartan administration may have advantages over benazepril administration for cats with renal or cardiovascular disease.

Chronic Kidney Disease in Aged Cats: Clinical Features, Morphology, and Proposed Pathogeneses

Chronic kidney disease (CKD) is the most common metabolic disease of domesticated cats, with most affected cats being geriatric (>12 years of age). The prevalence of CKD in cats exceeds that observed in dogs, and the frequency of the diagnosis of CKD in cats has increased in recent decades. Typical histologic features include interstitial inflammation, tubular atrophy, and fibrosis with secondary glomerulosclerosis. In contrast to people and dogs, primary glomerulopathies with marked proteinuria are remarkably rare findings in cats. Although a variety of primary renal diseases have been implicated, the disease is idiopathic in most cats. Tubulointerstitial changes, including fibrosis, are present in the early stages of feline CKD and become more severe in advanced disease. A variety of factors-including aging, ischemia, comorbid conditions, phosphorus overload, and routine vaccinations-have been implicated as factors that could contribute to the initiation of this disease in affected cats. Factors that are related to progression of established CKD, which occurs in some but not all cats, include dietary phosphorus intake, magnitude of proteinuria, and anemia. Renal fibrosis, a common histologic feature of aged feline kidneys, interferes with the normal relationship between peritubular capillaries and renal tubules. Experimentally, renal ischemia results in morphologic changes similar to those observed in spontaneous CKD. Renal hypoxia, perhaps episodic, may play a role in the initiation and progression of this disease.

Consensus recommendations for standard therapy of glomerular disease in dogs

Standard therapy forms the basic foundation for care of dogs with glomerular disease, as it is herein recommended for use in all affected animals regardless of causation of the disease. Consensus recommendations target the evaluation and management of proteinuria, inhibition of the renin-angiotensin-aldosterone system, modification in dietary intake with special consideration for those nutrients with renal effects, diagnosis and treatment of systemic hypertension, and evaluation and management of body fluid volume status in dogs with glomerular disease.

Plasma renin activity and aldosterone concentrations in hypertensive cats with and without azotemia and in response to treatment with amlodipine besylate

Background

Role of renin‐angiotensin aldosterone system (RAAS) in feline systemic hypertension is poorly understood.

Objectives

Examine plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) in normotensive and hypertensive cats with variable renal function and in response to antihypertensive therapy.

Animals

One hundred and ninety‐six cats >9 years from first opinion practice.

Methods

PRA, PAC, and aldosterone‐to‐renin ratio (ARR) were evaluated in cats recruited prospectively and grouped according to systolic blood pressure (SBP) and renal function (nonazotemic normotensive [Non‐Azo‐NT], nonazotemic hypertensive [Non‐Azo‐HT], azotemic normotensive [Azo‐NT], azotemic hypertensive [Azo‐HT]). Changes in PRA and PAC were evaluated with antihypertensive therapy (amlodipine besylate).

Results

Plasma renin activity (ng/mL/h; P = .0013), PAC (pg/mL; P < .001), and ARR (P = 0.0062) differed significantly among groups. PRA (ng/mL/h) was significantly lower in hypertensive (Non‐Azo‐HT; n = 25, median 0.22 [25th percentile 0.09, 75th percentile 0.39], Azo‐HT; n = 44, 0.33 [0.15, 0.48]) compared with Non‐Azo‐NT cats (n = 57, 0.52 [0.28, 1.02]). Azo‐HT cats had significantly higher PAC (n = 22, 149.8 [103.1, 228.7]) than normotensive cats (Non‐Azo‐NT; n = 26, 45.4 [19.6, 65.0], Azo‐NT; n = 18, 84.1 [38.6, 137.8]). ARR was significantly higher in Azo‐HT (n = 20, 503.8 [298.8, 1511]) than Azo‐NT cats (n = 16, 97.8 [77.0, 496.4]). Significant increase in PRA was documented with antihypertensive therapy (pretreatment [n = 20] 0.32 [0.15–0.46], posttreatment 0.54 [0.28, 1.51]), but PAC did not change.

Conclusions and Clinical Importance

Hypertensive cats demonstrate significantly increased PAC with decreased PRA. PRA significantly increases with antihypertensive therapy. Additional work is required to determine the role of plasma aldosterone concentration in the pathogenesis of hypertension and whether this relates to autonomous production or activation of RAAS without demonstrable increase in PRA.

Feline CKD: New horizons - where do we go from here?

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is common in humans as well as in cats, and is a significant human health problem. In feline medicine, despite recent research and improvements in our understanding of the condition, management remains limited by late diagnosis and an inadequate ability to prevent progression of disease. Investigation of future treatments that both delay the progression of CKD and manage clinical signs, and that are also easy and cost effective to administer, is desirable. To this end, we may learn from our colleagues in the medical profession.

AUDIENCE

CKD is commonly encountered in general practice and so all practitioners dealing with cats will benefit from understanding future treatment possibilities and interventions in the management of CKD.

EVIDENCE BASE

Large-scale medical studies have been performed to provide an evidence base for treatment decisions in human CKD. Several studies in cats have looked at various aspects of treatment and prognosis, but large-scale studies are needed to assess the benefits of treatments such as angiotensin-converting enzyme inhibitors and angiotensin receptor blockers.

CLINICAL CHALLENGES

Providing treatment that is effective, easy to administer and not cost-prohibitive is the challenge currently faced by clinicians in the management of feline CKD.

Feline CKD: Pathophysiology and risk factors--what do we know?

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is one of the most frequently encountered disorders in cats, having increased in prevalence in recent decades. Although the underlying cause is rarely identified, the common final outcome of feline CKD is tubulointerstitial fibrosis. Knowledge of CKD pathophysiology is necessary for optimal individualised patient management, especially with regard to diagnosis and treatment of extrarenal complications.

PATIENT GROUP

CKD is most common in senior and geriatric cats, but should be considered in any feline patient with ureterolithiasis, hyperthyroidism, retrovirus infection, systemic hypertension, cardiovascular disease or urinary tract infection.

EVIDENCE BASE

Most of our knowledge of the pathogenesis of CKD is extrapolated from human nephrology and experimental animal studies. There is, therefore, a need for further studies in cats. The prevalence of clinical signs in feline CKD is well documented. Several concurrent diseases associated with CKD have also been reported in cats, especially in the geriatric population, but there is no or only limited published evidence demonstrating a cause-and-effect relationship between most of these conditions and CKD. Studies performed over the past 15 years have nevertheless allowed identification of major risk factors (proteinuria, plasma phosphate and plasma creatinine) influencing the progression of feline CKD.

CLINICAL CHALLENGES

Clinical signs occur in the late stages of renal disease, so populations at higher risk of CKD should be screened routinely. CKD-associated complications (systemic hypertension, secondary renal hyperparathyroidism, hypokalaemia, anaemia, metabolic acidosis) must not be overlooked as they may affect the progression of disease. Disease progression is itself unpredictable and renal function may remain stable for extended periods. Most cats with early CKD do not progress to end-stage CKD before they die.

AUDIENCE

General practitioners play a major role in screening feline patients at risk of development or progression of CKD.

Feline CKD: Current therapies - what is achievable?

PRACTICAL RELEVANCE

Treatment of feline chronic kidney disease (CKD) tends to focus on minimising the adverse effects of reduced renal function, rather than addressing an underlying cause. Despite this, and the progressive nature of CKD, treatment can improve quality of life and enable many cats to have long survival times.

EVIDENCE BASE

Strong evidence supports the provision of renal diets, which are protein and phosphorus restricted; compliance is improved by gradual dietary transition. Additional phosphorus restriction is achieved by the use of phosphate binding agents, although it is unknown if these yield similar survival benefits to those provided by renal diets. Interventions to control hypokalaemia and hypertension in affected cats are important to prevent serious complications. Administration of benazepril to cats with proteinuric kidney disease has been shown to significantly improve their appetite but not their survival. As CKD progresses, many cats will benefit from treatment to control clinical signs of uraemic gastroenteritis and anaemia.

Hypertension in small animal kidney disease

Kidney disease is commonly associated with hypertension in dogs, cats and other species. There are multiple mechanisms underlying the development of renal hypertension including sodium retention, activation of the renin-angiotensin system and sympathetic nerve stimulation. The relative importance of these and other mechanisms may vary both between species and according to the type of kidney disease that is present. Consideration of underlying disease mechanisms may aid in the rational choice of therapy in hypertensive patients.

Feline systemic hypertension: Classification and pathogenesis

PRACTICAL RELEVANCE

the increased availability of indirect blood pressure monitoring devices in clinical practice over the past decade has highlighted the significance of systemic hypertension in the feline population. Without routine monitoring and appropriate intervention, cats with undiagnosed systemic hypertension may first be presented with sudden-onset blindness as a consequence of either hyphaema or retinal detachment.

CLINICAL CHALLENGES

the primary aim in the early diagnosis and treatment of systemic hypertension is prevention of hypertensive target organ damage (with respect to the eye, kidney, cardiovascular and central nervous systems, in particular). A prerequisite is a knowledge of the pathophysiological mechanisms and disease conditions that may contribute to the development of hypertension. This allows the clinician to determine those cases in which blood pressure assessment and longitudinal monitoring is essential and can assist in determining appropriate therapeutic strategies for control of blood pressure. Recent studies have also begun to explore the relationship that systemic hypertension may have with proteinuria and the progression of kidney disease.

PATIENT GROUP

the geriatric cat appears most susceptible to the development of systemic hypertension, and monitoring of systolic blood pressure is often advocated as part of a routine health screen in cats over 9-12 years old. Consideration must also be given to cats suspected of having an underlying disease such as chronic kidney disease or hyperthyroidism, or which are receiving therapeutic agents, irrespective of their age.

EVIDENCE BASE

much of our understanding of the pathogenesis of feline hypertension is extrapolated from studies performed in experimental animal models or in human patients, and interspecies differences are often poorly understood.

The cat with neurological manifestations of systemic disease. Key conditions impacting on the CNS

PRACTICAL RELEVANCE

A number of systemic diseases are associated with neurological deficits. Most systemic diseases that impact on the nervous system result in multifocal neurological signs; however, isolated deficits can also be observed. This article reviews the clinical signs, pathophysiology, diagnosis, treatment and prognosis of four important systemic diseases with neurological consequences: feline infectious peritonitis, toxoplasmosis, hypertension and hepatic encephalopathy.

CLINICAL CHALLENGES

Early recognition of systemic signs of illness in conjunction with neurological deficits will allow for prompt diagnosis and treatment. While neurological examination of the feline patient can undoubtedly be challenging, hopefully the accompanying articles in this special issue will enable the clinician to approach these cases with more confidence.

EVIDENCE BASE

The veterinary literature contains numerous reports detailing the impact of systemic disease on the nervous system. Unfortunately, very few references provide detailed descriptions of large cohorts of affected cats. This review summarises the literature underpinning the four key diseases under discussion.

Therapies for feline chronic kidney disease. What is the evidence?

Practical relevance Successful treatment and prevention of kidney disease in pet animals requires a multidimensional approach to identify and eliminate causes or exacerbating factors, provide professional examination and care on a regular basis, and plan and implement a comprehensive treatment program when necessary.

Evidence base Over the years, many therapeutic and preventive interventions have been developed or advocated for chronic kidney disease (CKD), but evidence of efficacy or effectiveness is often lacking or highly variable. Accordingly, the main objective of this systematic review was to identify and critically appraise the evidence supporting various approaches to managing feline CKD; namely, fluid therapy, calcitrioi therapy, antihypertensive therapy, ACE inhibitor therapy, erythropoietic hormone replacement therapy, potassium supplementation, antioxidant supplementation, alkalinization therapy, dietary phosphorus restriction and intestinal phosphate binders, therapeutic renal foods, assisted feeding, dialysis and renal transplantation.

Development of hypertension and effects of benazepril hydrochloride in a canine remnant kidney model of chronic renal failure

In order to determine whether hypertension would develop in dogs with chronic renal failure, we performed 7/8 renal ablation in 6 healthy dogs and compared pre- and post-ablation blood pressures determined by telemetry. One month after the renal ablation, blood urea nitrogen and creatinine were significantly increased (p<0.05), creatinine clearance was decreased (p<0.05), and blood pressure was increased significantly (p<0.05). Simultaneously, plasma renin activity, angiotensin I and II, and aldosterone were elevated significantly (p<0.05) compared with the values obtained from 11 healthy dogs with intact renal function. The dogs with induced renal failure and hypertension were administered an angiotensin-converting enzyme inhibitor, benazepril hydrochloride, once daily for 2 weeks at 2 mg/kg body weight, and changes in blood pressure and the renin-angiotensin-aldosterone (RAA) system were determined. During the administration of benazepril hydrochloride, blood pressure, angiotensin II and aldosterone decreased significantly (p<0.05) and, upon discontinuation of administration, increased to the pre-administration levels (p<0.05). Plasma renin activity and angiotensin I showed no significant changes throughout the administration study. These results provide experimental evidence that hypertension develops in dogs with chronic renal failure through mechanisms involving the RAA system and demonstrate that benazepril hydrochloride improves renal hypertension in dogs.

Pharmacokinetics and pharmacodynamics of ramipril and ramiprilat in healthy cats

The pharmacokinetics of ramipril and its active metabolite, ramiprilat, was determined in cats following single and repeated oral doses of ramipril (Vasotop tablets) (once daily for 9 days) at dose rates of 0.125, 0.25, 0.5 and 1.0 mg/kg. The pharmacodynamic effects were assessed by measuring plasma angiotensin-converting enzyme (ACE) activity. Maximum ramipril concentrations were attained within 30 min following a single dose and declined rapidly (concentrations were below the limit of quantification 4 h after treatment). Peak ramiprilat concentrations were detected at approximately 1.5 h. The apparent terminal half-life (t((1/2)beta)) was > or =20 h irrespective of the dose. Ramiprilat accumulated in plasma (ratio of accumulation 1.3 to 1.9 depending on the dose rate) following repeated administration. Steady-state conditions were attained after the second dose. Excretion was predominant in faeces (87%) and to a lesser extent in urine (11%). The rate and extent of absorption of ramipril as well as its conversion to ramiprilat were not significantly influenced by the presence of food in the gastrointestinal tract. Plasma-ACE activity was almost completely abolished 0.5-2.0 h after treatment, irrespective of the dose rate. Significant inhibition of ACE activity of 54.7 to 82.6% (depending on the dosage) was still present 24 h after treatment. Treatment was well-tolerated in all cats. Ramipril at a dose rate of 0.125 mg/kg once daily produces significant and long-lasting inhibition of ACE activity in healthy cats. The appropriateness of this dosage regime needs to be confirmed in diseased cats.

Persistent haematuria and proteinuria due to glomerular disease in related Abyssinian cats

Eight cases of glomerular disease in young, related Abyssinian cats are described. Haematuria was the most consistent feature. Six cats developed the nephrotic syndrome. The short-term prognosis was good for cats with haematuria and fair for cats with the nephrotic syndrome as oedema resolved in three of the six cats. Light microscopic examination of renal biopsies from three cats was considered normal or revealed only mild abnormalities. In the three cases subjected to necropsy, histological abnormalities included mild mesangial hypercellularity and adhesions between the glomerular tuft and Bowman's capsule consistent with a focal proliferative glomerulopathy. Further investigation into this glomerulopathy will require ultrastructural and immunohistochemical studies to characterise the glomerular abnormality and genetic analyses to investigate its potential to be an inherited disease. Glomerular disease, potentially a familial one, should be considered in the investigation of persistent haematuria or proteinuria in Abyssinian and related cats.

Pharmacologic Management of Feline Hyperthyroidism

Radioiodine is considered the treatment of choice for hyperthyroidism, but in some situations, methimazole therapy is preferred, such as in cats with preexisting renal insufficiency. Unfavorable outcomes from methimazole are usually attributable to side effects, such as gastrointestinal upset, facial excoriation, thrombocytopenia, neutropenia, or liver enzyme elevations. Because restoration of euthyroidism can lead to a drop in glomerular filtration rate, all cats treated with methimazole should be monitored with blood urea nitrogen and creatinine levels in addition to serum thyroxine (T(4)) and a complete blood cell count. Transdermal methimazole is associated with fewer gastrointestinal side effects and can be used in cats with simple vomiting or inappetence from oral methimazole. Hypertension may not resolve immediately when serum T(4) is normalized, and moderate to severe hypertension should be treated concurrently with atenolol, amlodipine, or an angiotensin-converting enzyme inhibitor.

Medical management of hyperthyroidism

Radioiodine is considered the treatment of choice for hyperthyroidism, but in some situations, methimazole therapy is preferred, such as in cats with pre-existing renal insufficiency. Methimazole blocks thyroid hormone synthesis, and controls hyperthyroidism in more than 90% of cats that tolerate the drug. Unfavorable outcomes are usually due to side effects such as gastrointestinal (GI) upset, facial excoriation, thrombocytopenia, neutropenia, or liver enzyme elevations; warfarin-like coagulopathy or myasthenia gravis have been reported but are rare. Because restoration of euthyroidism can lead to a drop in glomerular filtration rate, all cats treated with methimazole should be monitored with BUN and creatinine, in addition to serum T4, complete blood count, and liver enzymes. Transdermal methimazole is associated with fewer GI side effects, and can be used in cats with simple vomiting or inappetance from oral methimazole. Hypertension may not resolve immediately when serum T4 is normalized, and moderate to severe hypertension should be treated concurrently with-atenolol, amlodipine, or an ACE inhibitor. Alternatives to methimazole include carbimazole, propylthiouracil, or iodinated contrast agents.

Diurnal variations of blood pressure in cats

Blood pressure (BP) was analyzed invasively using the telemetry system in unanesthetized, unrestrained healthy adult mongrel cats. After surgical implantation of a telemetry transmitter, BP was transiently elevated due to the invasive nature of the surgery, but it was gradually decreased. BP was largely stabilized seven to ten days postsurgery. Once BP was settled, systolic, diastolic and mean BPs(2) were obtained at 5-min intervals in individual cats. Hourly averages of these BP values revealed a diurnal variation with two peaks at 8:00 and 19:00. We also found that BP was significantly higher when cats were active compared to when they were sleeping or at rest (p<0.05). The average 24-hr BP in 20 healthy cats was 118.4+/-11.0 (systolic), 78.0+/-8.7 (diastolic) and 94.8+/-9.5 mmHg (mean) by the telemetry system.

Effects of administration of fluids and diuretics on glomerular filtration rate, renal blood flow, and urine output in healthy awake cats

OBJECTIVES

To determine effects of commonly used diuretic treatments on glomerular filtration rate (GFR), renal blood flow (RBF), and urine output (UO) and compare 2 methods of GFR measurement in healthy awake cats.

ANIMALS

8 healthy cats.

PROCEDURE

In a randomized crossover design, cats were randomly allocated to 4 groups: control; IV administration of fluids; IV administration of fluids and mannitol; and IV administration of fluids, dopamine, and furosemide. Inulin and para-aminohippuric acid were used for determination of plasma clearance for GFR and RBF, respectively. Plasma clearance of technetium-Tc-99m-diethylenetriaminepentacetic acid (99mTc-DTPA) was also used for GFR determination.

RESULTS

Furosemide-dopamine induced the largest UO, compared with other groups. Both mannitol and fluid therapy increased RBF, compared with the control group. Mannitol, and not fluid therapy, increased RBF, compared with furosemide-dopamine. There were significant differences in GFR values calculated from 99mTc-DTPA and inulin clearances between the 2 groups. In all groups, use of 99mTc-DTPA caused underestimation of GFR, compared with use of inulin.

CONCLUSIONS AND CLINICAL RELEVANCE

In healthy awake cats, administration of furosemide-dopamine did not increase GFR or RBF despite increased UO. Fluid therapy and fluid therapy plus mannitol improved RBF. Determination of GFR by use of 99mTc-DTPA cannot always be substituted for inulin clearance when accurate measurement is required.