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

Case report: Resolution of oligo-anuric acute kidney injury with furosemide administration in a cat following lily toxicity

Objective

To describe the successful outcome of a case of oligo-anuric acute kidney injury in a cat secondary to lily ingestion.

Case summary

A 12-week-old intact male domestic short-hair cat weighing 1.64 kg (3.6 lb) presented with a 12-h duration of vomiting and lethargy after exposure to lilies of the genera Lilium species 24 h prior to presentation. Severe azotemia (Creatinine 5.8 mg/dL, BUN > 100 mg/dL) and hyperkalemia (9.36 mmol/L) were noted on the day of presentation. Treatment of hyperkalemia was instituted with calcium gluconate, lactated ringers solution, dextrose, regular short-acting insulin, albuterol, and sodium bicarbonate, Oliguria to anuria was highly suspected based on a lack of urine production 21 h after hospitalization with intravenous fluid administration and a static bladder size. The cat was administered 4 mg/kg of furosemide, and urinated at 6 h following administration and continued to produce over 6 ml/kg/h of urine in the next 24 h. Two days following furosemide administration, the cat's hyperkalemia and azotemia resolved. The cat was discharged after 4 days of hospitalization, and a recheck revealed no persistent azotemia or hyperkalemia.

Unique information

Anuric acute kidney injury secondary to lily toxicity is associated with a poor prognosis, and the only treatment modality previously described is hemodialysis. The cat in this report was successfully managed with medical intervention and furosemide administration, with complete resolution of the acute kidney injury.

Methods for Assessment of the Glomerular Filtration Rate in Laboratory Animals

Background

The glomerular filtration rate (GFR), as the benchmark of renal function, has been widely used in clinical practice and basic medical research. Currently, most researchers still rely on endogenous markers, such as plasma creatinine, blood urea nitrogen, and cystatin C, to evaluate renal function in laboratory animals. While inexpensive and simple to use, methods based on endogenous markers are often inaccurate and susceptible to several internal physiological factors. Thus, it is necessary to establish a method to precisely assess the GFR, especially when detecting early changes in GFR during acute kidney injury, and hyperfiltration usually caused by pregnancy or diabetic nephropathy. In addition, laboratory animals have higher tolerance for invasive procedures than humans, allowing novel technologies to be applied on them for GFR monitoring. In recent years, significant progress has been made in developing new methods to assess GFR in animals. However, no publication has reviewed these techniques.

Summary

This article summarized the majority of methods used to assess the GFR in animals in recent decades and discussed their working principles, workflows, advantages, and limitations, providing a wealth of reference and information for researchers interested in studying the kidney function in animals and developing techniques to monitor the GFR.

Development and validation of an ultra-high performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of iohexol, p-aminohippuric acid and creatinine in porcine and broiler chicken plasma

In order to study the renal function, in terms of glomerular filtration and effective renal plasma flow, in broiler chickens and pigs, an ultra-high performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of iohexol, p-aminohippuric acid (PAH) and exogenously administered creatinine in plasma was developed and validated. Sample preparation consisted of a deproteinization step using methanol for porcine plasma and an Ostro™ Protein Precipitation & Phospholipid Removal Plate was used for broiler chicken plasma. Chromatographic separation was achieved on a Hypersil Gold aQ column using 0.1% formic acid in water and 0.1% formic acid in methanol as mobile phases. The total run time was limited to 10 min. Matrix-matched calibration curves for iohexol and PAH were prepared and good linearity (r ≥ 0.9973; gof ≤ 6.17%) was achieved over the concentration range tested (0.25-90 μg/mL). Limits of quantification were 0.25 μg/mL for iohexol and PAH. Water was used as surrogate matrix for analysis of creatinine in plasma. This surrogate calibration curve showed good linearity over the concentration range tested (0.25-90 μg/mL) (r ≥ 0.9979; gof ≤ 5.66%). For creatinine, the relative lower limit of quantification was 201.03 ± 49.20% and 60.14 ± 7.64% for chicken and porcine plasma, respectively. The results for within-day and between-day precision and accuracy fell within the specified ranges. This straightforward, cost-effective and rapid method, determining iohexol, PAH and creatinine within one single chromatographic run, has been successfully used for the analysis in porcine and broiler chicken plasma samples in order to determine the renal function of these species.

Mechanisms of triple whammy acute kidney injury

Pre-renal acute kidney injury (AKI) results from glomerular haemodynamic alterations leading to reduced glomerular filtration rate (GFR) with no parenchymal compromise. Renin-angiotensin system inhibitors, such as angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor antagonists (ARAs), non-steroidal anti-inflammatory drugs (NSAIDs) and diuretics, are highly prescribed drugs that are frequently administered together. Double and triple associations have been correlated with increased pre-renal AKI incidence, termed "double whammy" and "triple whammy", respectively. This article presents an integrative analysis of the complex interplay among the effects of NSAIDs, ACEIs/ARAs and diuretics, acting alone and together in double and triple therapies. In addition, we explore how these drug combinations alter the equilibrium of regulatory mechanisms controlling blood pressure (renal perfusion pressure) and GFR to increase the odds of inducing AKI through the concomitant reduction of blood pressure and distortion of renal autoregulation. Using this knowledge, we propose a more general model of pre-renal AKI based on a multi whammy model, whereby several factors are necessary to effectively reduce net filtration. The triple whammy was the only model associated with pre-renal AKI accompanied by a course of other risk factors, among numerous potential combinations of clinical circumstances causing hypoperfusion in which renal autoregulation is not operative or is deregulated. These factors would uncouple the normal BP-GFR relationship, where lower GFR values are obtained at every BP value.

Plasma exogenous creatinine clearance in clinically healthy cats: comparison with urinary exogenous creatinine clearance, tentative reference intervals and indexation to bodyweight

Glomerular filtration rate (GFR) is considered to be the best indicator of overall kidney function. The major objectives of this study were to compare plasma exogenous creatinine clearance (PECC) with a reference method, to establish reference intervals (RIs) for PECC and to assess the effects of indexation of GFR to bodyweight (BW) in cats. PECC was compared with urinary clearance of exogenous creatinine (UECC) in six clinically healthy domestic shorthair cats (experiment 1). Tentative RIs were determined according to current guidelines and the effects of indexation to BW and of covariables on GFR were assessed in 43 clinically healthy cats of various breeds (experiment 2). PECC was 15% higher than UECC (P <0.01), but the two estimates were strongly correlated (r(2)=0.97, P = 0.001). RIs for PECC were 6.4-21.3 mL/min or 1.2-4.9 mL/min/kg. The absolute (i.e. non-indexed) GFR value was not dependent on BW. Thus, indexation of GFR to BW in cats would not standardize the GFR value, but could introduce bias in clinical interpretation. Significant effects of breed, plasma protein concentration and plasma albumin concentration on GFR were demonstrated. Plasma concentrations of urea and creatinine, when assessed separately, were also weakly correlated with GFR in healthy cats. These combined findings contribute to a better understanding of renal function assessment in cats.

Measurement of glomerular filtration rate in cats: methods and advantages over routine markers of renal function

PRACTICAL RELEVANCE

Routinely used markers of renal function in clinical practice include urea and creatinine. However, these are insensitive markers, particularly in the early stages of kidney disease. Measurement of glomerular filtration rate (GFR) is regarded as the most sensitive index of functioning renal mass. It may be useful for feline patients in varying clinical scenarios; for example, where a more accurate measurement of renal function may aid diagnosis, to enable response to therapeutic interventions to be more closely monitored, or to evaluate renal function prior to the use of nephrotoxic or renally cleared drugs.

CLINICAL CHALLENGES

Traditional methods of measuring GFR, such as renal clearance or multisample plasma clearance techniques, are generally impractical for clinical use. Limited sampling and single sample plasma clearance methods using the filtration marker iohexol have been validated in cats. These have the advantages of reduced stress to cats associated with repeated sampling and reduced costs of analysis, and therefore offer greater clinical utility. Attempts to develop an estimated GFR (eGFR) formula similar to that used in human patients have been made in cats, although currently an accurate and reliable formula is not available.

AUDIENCE

This review presents the basis for the theoretical understanding and practical measurement of GFR for any veterinary practitioner wishing to obtain a more accurate and sensitive assessment of renal function than routinely used markers provide.

EVIDENCE BASE

The review draws evidence from peer-reviewed publications, the author's PhD thesis and also clinical experience.

Feline acute kidney injury: 2. Approach to diagnosis, treatment and prognosis

PRACTICAL RELEVANCE

Feline acute kidney injury (AKI) is a commonly recognized problem in small animal practice that requires prompt diagnosis and directed therapy. There are many treatment methods with which practitioners should be familiar, including medical options, surgical interventions and renal replacement therapy (dialysis). It is important to know which option is most appropriate for each cause and stage of AKI to deliver the most effective therapy.

CLINICAL CHALLENGES

AKI can cause vague clinical signs, but a vast array of life-threatening sequelae. Rapid recognition of potential complications and knowledge of treatment options is imperative for successful management. Feline patients also require an understanding of their unique physiology as it relates to the therapeutic plan.

AUDIENCE

This two-part review article is directed at small animal practitioners as well as specialists. Part 2 discusses the diagnosis of AKI in cats using physical examination findings, clinicopathologic results and imaging modalities. The treatment of AKI and its sequelae is also reviewed, with information on recent advances in this area.

EVIDENCE BASE

While there is very limited data comparing the outcomes of various treatment options, there is literature addressing the use of several medications, as well as renal replacement therapy, in cats.

An overview of glomerular filtration rate testing in dogs and cats

Determination of glomerular filtration rate (GFR) is a valuable, yet underused, diagnostic tool for evaluating renal function in dogs and cats. This article first reviews the hormonal and hemodynamic factors which contribute to GFR, followed by a description of considerations when selecting a pharmacokinetic model and methods of animal-to-animal standardization. The best-characterized existing GFR markers, including creatinine, radiolabeled markers, and iohexol, are reviewed in depth, as well as alternative but lesser used techniques. A weighted means analysis of reported GFR measurements in healthy dogs and cats and a review of selected studies that have examined GFR alterations in animals with naturally occurring and experimental diseases provide the reader with preliminary guidelines on expected GFR results in these species and disease conditions.

Single-dose pharmacokinetics of oxytetracycline and penicillin G in tammar wallabies (Macropus eugenii)

The pharmacokinetics of oxytetracycline and penicillin G was investigated in tammar wallabies (Macropus eugenii). Groups of eight healthy tammar wallabies were administered i.v. oxytetracycline hydrochloride (40 mg/kg), i.m. long-acting-oxytetracycline (20 mg/kg), i.v. sodium penicillin G (30 mg/kg), or i.m. procaine/benzathine penicillin G (30 mg/kg). Plasma concentrations of oxytetracycline were determined using high-performance liquid chromatography. Pharmacokinetic parameters were comparable to those reported for eutherians of equivalent size and suggest that the practice of adjusting allometrically scaled doses to account for the lower metabolic rate of marsupials may not be valid. Long-acting oxytetracycline and penicillin G both demonstrated depot effects. However, the plasma concentrations achieved question the therapeutic efficacy of the long-acting preparations.

Evaluation of serum iohexol clearance for use in predicting carboplatin clearance in cats

OBJECTIVE

To determine whether a glomerular filtration rate (GFR) assay based on serum iohexol clearance can be used to predict carboplatin clearance in cats.

ANIMALS

10 cats with tumors.

PROCEDURES

GFR was measured concurrently by use of plasma clearance of technetium Tc 99m-labeled diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) to yield GFR(99mTc-DTPA) and serum clearance of iohexol to yield GFR(Iohexol). A single dose of carboplatin was administered IV as a bolus. Dose was calculated by use of a target value for the area under the plasma platinum concentration-versus-time curve (AUC(Target)) and estimation of platinum clearance (CL(PT)) derived from GFR(99mTc-DTPA) as follows: dose = AUC(Target) x 2.6 x GFR(99mTc-DTPA) x body weight, where AUC(Target) is 2.75 min.mg.mL(-1). Plasma platinum concentrations were measured via atomic absorption spectrophotometry. Values for GFR(99mTc-DTPA) and GFR(Iohexol) were compared by use of least-squares regression and Bland-Altman analysis. Least-squares regression was used to determine whether CL(PT) could be predicted from GFR(99mTc-DTPA) or GFR(Iohexol) (or both).

RESULTS

GFR(99mTc-DTPA) and GFR(Iohexol) were strongly correlated (r = 0.90), but GFR(Iohexol) values were significantly larger by a factor of approximately 1.4. Platinum clearance had a significant linear relationship to GFR(99mTc-DTPA) (CL(PT) = 2.5 x GFR(99mTc-DTPA)) and to GFR(Iohexol) (CL(PT) = [1.3 x GFR(Iohexol)] + 1.4).

CONCLUSIONS AND CLINICAL RELEVANCE

In cats, serum iohexol clearance was an accurate predictor of CL(PT) and can be used to calculate the carboplatin dose as follows: dose = AUC(Target) x ([1.3 x GFR(Iohexol)] + 1.4) x body weight.

Comparison of plasma clearance of exogenous creatinine, exo-iohexol, and endo-iohexol over a range of glomerular filtration rates expected in cats

The study investigated plasma clearance of exogenous creatinine (PECCT), exo-iohexol (PexICT) and endo-iohexol (PenICT) in six healthy cats, four cats with chronic kidney disease (CKD) and six hyperthyroid (HT) cats to assess potential differences in glomerular filtration rate (GFR) measurement over a wide range of GFR values. The PECCT, PexICT and PenICT were performed in a combined protocol. There was a significant difference between PexICT and PenICT and PECCT in healthy cats. Differences between clearance techniques are suggested to be correlated to range in GFRs and should be taken into account when GFR is measured.

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.