Estimation of glomerular filtration rate by plasma clearance of iohexol in healthy horses of various ages

The combination of trailer transport and exercise increases gastrointestinal permeability and markers of systemic inflammation in horses

BACKGROUND

Leaky gut syndrome (LGS) is an idiopathic disorder characterised by alterations in intestinal permeability and low-grade systemic inflammation. Factors contributing to development of LGS are not well-understood but physiological stressors such as exercise and transport may play a role which may be of pathophysiological relevance in horses.

OBJECTIVES

To characterise the combined effect of transport stress and exercise on gastrointestinal permeability, and to determine whether these effects are associated with increased inflammatory biomarkers in plasma.

STUDY DESIGN

Controlled, randomised and cross-over study.

METHODS

Horses (n = 8 per group) were given a gastrointestinal permeability tracer (iohexol; 5.6% solution; 1 ml/kg bwt) via nasogastric entubation prior to being assigned to a stressed (EX; 1 h of trailer transport immediately followed by 30 min moderate intensity exercise; n = 4) or sedentary control (CON; n = 4) group. Plasma samples were obtained prior to iohexol administration (P1), after transport (P2), at exercise cessation (P3), and at 1 (P4), 2 (P5), 4 (P6) and 8 (P7) hours after cessation of exercise and were analysed for iohexol, inflammatory biomarkers (SAA, LPS, IFABP and LBP) and tight junction proteins (zonulin). Faecal samples were collected at times corresponding to before and after stress from both groups and analysed for zonulin. Data were analysed using a 2-way RM ANOVA.

RESULTS

In EX horses, a significant increase in iohexol was observed at P2 (1.5 ± 0.24 μg/ml; p = 0.03), P3 (2.1 ± 0.29 μg/ml; p < 0.001), P4 (2.1 ± 0.17 μg/ml; p < 0.001) compared with P1 (0.7 ± 0.21 μg/ml); iohexol was significantly higher in EX than CON horses at P3 (p < 0.001), P4 (p < 0.001) and P5 (p = 0.003). LPS and SAA were significantly higher in EX than CON at P4 (p < 0.001) and P6 (p = 0.04), respectively.

MAIN LIMITATIONS

Data from our small sample size may not be generalisable to the larger equine population.

CONCLUSIONS

Combined transport and exercise increases gastrointestinal permeability and systemic SAA and LPS. The model described herein may be useful in further studies on the role of alterations in gastrointestinal permeability in equine disease.

Advanced Strategies of Drug Delivery via Oral, Topical, and Parenteral Administration Routes: Where Do Equine Medications Stand?

While the global market for veterinary products has been expanding rapidly, there is still a lack of specialist knowledge of equine pharmaceutics. In many cases, the basic structure of the gastrointestinal tract (GIT) and integumentary system of the horse shares similarities with those of humans. Generally, the dosage form developed for humans can be repurposed to deliver equine medications; however, due to physiological variation, the therapeutic outcomes can be unpredictable. This is an area that requires more research, as there is a clear deficiency in literature precedence on drug delivery specifically for horses. Through a careful evaluation of equine anatomy and physiology, novel drug delivery systems (NDDSs) can be developed to adequately address many of the medical ailments of the horse. In addition to this, there are key considerations when delivering oral, topical, and parenteral drugs to horses, deriving from age and species variation. More importantly, NDDSs can enhance the duration of action of active drugs in animals, significantly improving owner compliance; and ultimately, enhancing the convenience of product administration. To address the knowledge gap in equine pharmaceutical formulations, this paper begins with a summary of the anatomy and physiology of the equine gastrointestinal, integumentary, and circulatory systems. A detailed discussion of potential dosage-form related issues affecting horses, and how they can be overcome by employing NDDSs is presented.

Population Pharmacokinetic Model of Iohexol in Dogs to Estimate Glomerular Filtration Rate and Optimize Sampling Time

Monitoring iohexol plasma clearance is considered a useful, reliable, and sensitive tool to establish glomerular filtration rate (GFR) and early stages of kidney disease in both humans and veterinary medicine. The assessment of GFR based on iohexol plasma clearance needs repeated blood sampling over hours, which is not easily attainable in a clinical setting. The study aimed to build a population pharmacokinetic (Pop PK) model to estimate iohexol plasma clearance in a population of dogs and based on this model, to indicate the best sampling times that enable a precise clearance estimation using a low number of samples. A Pop PK model was developed based on 5 iohexol plasma samples taken from 5 to 180 minutes (min) after an intravenous iohexol nominal dose of 64.7 mg/kg from 49 client-owned dogs of different breeds, sexes, ages, body weights, and clinical conditions (healthy or presenting chronic kidney disease CKD). The design of the best sampling times could contain either 1 or 2 or 3 sampling times. These were discretized with a step of 30 min between 30 and 180 min. A two-compartment Pop PK model best fitted the data; creatinine and kidney status were the covariates included in the model to explain a part of clearance variability. When 1 sample was available, 90 or 120 min were the best sampling times to assess clearance for healthy dogs with a low creatinine value. Whereas for dogs with CKD and medium creatinine value, the best sampling time was 150 or 180 min, for CKD dogs with a high creatinine value, it was 180 min. If 2 or 3 samples were available, several sampling times were possible. The method to define the best sampling times could be used with other Pop PK models as long as it is representative of the patient population and once the model is built, the use of individualized sampling times for each patient allows to precisely estimate the GFR.

The Sick Adult Horse: Renal Clinical Pathologic Testing and Urinalysis

Clinicopathologic evaluation of renal function and renal disease in sick adult horses remains grounded in detection of azotemia, assessment of serum and urine electrolyte concentrations, and evaluation of urinalysis findings, including specific gravity, reagent strip analysis, and sediment examination. Because increases in serum or plasma urea nitrogen and creatinine concentrations are insensitive indicators of a decreased glomerular filtration rate, there is considerable interest in identifying novel biomarkers of renal function or injury in blood and urine, with serum symmetric dimethylarginine concentration being the most recent addition to the commercial market.

Estimation of glomerular filtration rate by plasma clearance of iohexol in healthy horses of various ages

Background

Plasma clearance of iohexol is a reliable method to assess the glomerular filtration rate (GFR). The relationship between aging and GFR in horses is unclear.

Hypothesis/Objectives

To compare GFR estimated by iohexol clearance in horses of different ages.

Animals

Twenty‐one clinically healthy horses were enrolled.

Methods

Prospective study. Groups: (A) composed by 8 young horses (≤14 years old) with serum creatinine <1.5 mg/dL, (B) by 7 aged horses (≥20 years old) with serum creatinine <1.5 mg/dL, and (C) by 6 aged horses (≥20 years old) with serum creatinine ≥1.5 mg/dL. Iohexol was injected (75.5 mg/kg) through an IV catheter, and plasma samples were collected 5, 30, and 90 minutes later. Plasma clearance of iohexol was obtained by the high‐performance liquid chromatography‐ultraviolet method.

Results

The GFR was 2., 2.1, and 1.45 mL/min/kg (median value) in Groups A, B, and C, respectively. Statistical analysis showed differences between Group A versus C for urea, Group A versus B and A versus C for creatinine, and A versus C for GFR.

Conclusions and Clinical Importance

Glomerular filtration rate was significantly reduced in aged horses with serum creatinine ≥1.5 mg/dL compared to young horses with creatinine <1.5 mg/dL; no differences were obtained between young and aged horses with creatinine <1.5 mg/dL. Glomerular filtration rate evaluation should be considered in aged horses even if the plasma creatinine values are normal.