Influence of Differences in Body Weight and Volume Management on Experimental Results in Porcine Models

Pharmacokinetics of glucagon after intravenous, intraperitoneal and subcutaneous administration in a pig model

Introduction

There is increasing scientific evidence to substantiate using low‐dose glucagon as a supplement to insulin therapy in artificial pancreata for diabetes mellitus type 1. The delivery of both these hormones intraperitoneally would mimic normal physiology. However, our knowledge of the pharmacological properties of glucagon after intraperitoneal administration is limited. This study compared the pharmacokinetics of glucagon after intraperitoneal, subcutaneous and intravenous administration and the pharmacodynamic effects of glucagon on glucose metabolism after intraperitoneal and subcutaneous administration in a pig model.

Materials and methods

Twelve pigs were included. Glucagon was administered intraperitoneally, subcutaneously and intravenously in a randomised order. Arterial samples were collected every 2–10 min for 150 min to determine plasma glucagon and blood glucose concentrations.

Results

The bioavailability of glucagon was significantly lower after intraperitoneal compared with subcutaneous administration with a median difference (95% confidence interval) of 13% (4–22). The effect of glucagon on glucose metabolism was equal after intraperitoneal and subcutaneous administration.

Conclusions

Intraperitoneal glucagon administration resulted in lower systemic glucagon exposure than subcutaneous administration without loss of efficiency. We interpret this as evidence of a major first‐pass metabolism of glucagon in the liver.

Pharmacokinetics of Intraperitoneally Delivered Glucagon in Pigs: A Hypothesis of First Pass Metabolism

Background and Objective

Artificial pancreases administering low-dose glucagon in addition to insulin have the scope to improve glucose control in patients with diabetes mellitus type 1. If such a device were to deliver both hormones intraperitoneally, it would mimic normal physiology, which may be beneficial. However, the pharmacokinetic properties of glucagon after intraperitoneal administration are not well known. Hence, the current study aims to evaluate the relationship between the amount of intraperitoneally delivered glucagon and pharmacokinetic variables in a pig model.

Methods

Pharmacokinetic data was retrieved from experiments on 19 anaesthetised pigs and analysed post hoc. The animals received a single intraperitoneal bolus of glucagon ranging from 0.30 to 4.46 µg/kg. Plasma glucagon was measured every 2–10 min for 50 min.

Results

Peak plasma concentration and area under the time–plasma concentration curve of glucagon correlated positively with the administered dose, and larger boluses provided a relatively greater increase. The mean (standard deviation) time to maximum glucagon concentration in plasma was 11 (5) min, and the mean elimination half-life of glucagon in plasma was 19 (7) min.

Conclusions

Maximum plasma concentration and area under the time–plasma concentration curve of glucagon increase nonlinearly in relation to the intraperitoneally administered glucagon dose. We hypothesise that the results are compatible with a satiable first-pass metabolism in the liver. Time to maximum glucagon concentration in plasma and the elimination half-life of glucagon in plasma seem independent of the drug dose.

Intraperitoneal and subcutaneous glucagon delivery in anaesthetized pigs: effects on circulating glucagon and glucose levels

Glucagon is a pancreatic hormone and increases the blood glucose levels. It may be incorporated in a dual hormone artificial pancreas, a device to automatically and continuously control blood glucose levels of individuals with diabetes. Artificial pancreas systems have been developed for use in the subcutaneous tissue; however, the systems are not fully automated due to slow dynamics. The intraperitoneal space is therefore investigated as an alternative location for an artificial pancreas. Glucose dynamics after subcutaneous and intraperitoneal glucagon delivery in ten anaesthetized pigs were investigated. The pigs received intraperitoneal boluses of 0.3 µg/kg and 0.6 µg/kg and a subcutaneous bolus of 0.6 µg/kg in randomized order. They also received an intraperitoneal bolus of 1 mg given at the end of the experiments to test the remaining capacity of rapid glucose release. Six pigs were included in the statistical analysis. The intraperitoneal glucagon bolus of 0.6 µg/kg gave a significantly higher glucose response from 14 to 30 min compared with the subcutaneous bolus. The results indicate that glucagon induces a larger glucose response after intraperitoneal delivery compared with subcutaneous delivery and is encouraging for the incorporation of glucagon in an intraperitoneal artificial pancreas.

Effect of intravenous albumin infusion on brain salicylate concentration

BACKGROUND

Salicylate poisoning appears to result in death, despite supportive care, once a critical brain salicylate concentration is reached. The binding of salicylate to albumin is saturable; free plasma salicylate concentrations rise disproportionately to total drug levels. Because unbound salicylate distributes into the brain, the authors questioned whether an intravenous (i.v.) infusion of albumin would cause a redistribution of salicylate from the brain back into the plasma, which might allow enough time for hemodialysis to be instituted.

OBJECTIVES

To determine if i.v. albumin infusion would lower brain salicylate concentrations through redistribution in a porcine model of acute salicylate poisoning.

METHODS

In a randomized controlled trial, 17 swine under anesthesia and controlled ventilation received 400 mg/kg of sodium salicylate i.v. over 15 minutes. At 60 minutes, nine animals received 1.25 g/kg albumin (25% solution) i.v. over 15 minutes, while eight control animals received an equal volume of normal saline (5 mL/kg). Arterial pH was maintained between 7.45 and 7.55. Serial measurements of serum albumin as well as free and total salicylate concentrations were obtained, and urine was collected for measurement of total salicylate excretion. At 180 minutes, animals were killed and brains harvested for measurement of brain salicylate concentrations.

RESULTS

Average peak serum total salicylate concentrations of 105.5 and 109 mg/dL were achieved in control and albumin-treated animals, respectively. Albumin infusion was accompanied by statistically significant increases in serum total salicylate concentrations (median from 79.5 to 86.9 mg/dL at 75 minutes), while levels decreased slightly in control animals. Serum free salicylate concentrations decreased slightly in albumin-treated animals, but the difference was not statistically significant. Median brain salicylate concentrations were about 14% lower in the albumin treatment group (17.8 mg/100 g brain) compared with controls (20.5 mg/100 g brain); this approached statistical significance (p = 0.075). Median urinary salicylate excretion was higher in the albumin-treated group (0.83 vs. 0.48 g; p = 0.072), with similar urinary pH and volumes in both groups.

CONCLUSIONS

In this animal model of salicylate poisoning, i.v. infusion of 1.25 g/kg albumin was accompanied by a 14% decline in median brain salicylate concentrations, which approached statistical significance.

Dual-lumen catheters for continuous venovenous hemofiltration: limits for blood delivery via femoral vein access and a potential alternative in an experimental setting in anesthetized pigs

Introduction

Small intravascular volume, pathophysiological hemorheology, and/or low cardiac output [CO] are assumed to reduce available blood flow rates via common dual-lumen catheters (except for those with a right atrium catheter tip position) in the critically ill patient. We performed an experimental animal study to verify these assumptions.

Methods

Anesthetized, ventilated pigs (35 to 50 kg) were allocated to different hemorheological conditions based on the application of different volume substitutes (that is, colloids and crystalloids, n = 6 to 7 per volume substitute). In a second step, allocation to the final study group was performed after the determination of the highest values for access flow (Qa) via an axial dual-lumen catheter (11 French, 20 cm long, side holes) placed in the femoral vein. High Qa rates (>300 ml/minute) were allocated to the dual-lumen catheter group; low Qa rates were switched to a 'dual-vein approach' using an alternative catheter (8.5-French sheath) for separate blood delivery. Hemodynamics (CO and central venous pressure [CVP]) and blood composition (blood cell counts, plasma proteins, and colloid osmotic pressure) were measured. Catheter tip positions and vessel diameters were exemplified by computed tomography.

Results

Forty-four percent of the animals required an alternative vascular access due to only minimal Qa via the dual-lumen catheter. Neither hemorheologically relevant aspects nor CO and CVP correlated with the Qa achievable via the femoral vein access. Even though the catheter tip of the alternative catheter provided common iliac vein but not caval vein access, this catheter type enabled higher Qa than the dual-lumen catheter positioned in the caval vein.

Conclusion

With respect to the femoral vein approach, none of the commonly assumed reasons for limited Qa via the arterial line of an axial dual-lumen catheter could be confirmed. The 8.5-French sheath, though not engineered for that purpose, performed quite well as an alternative catheter. Thus, in patients lacking right jugular vein access with tip positioning of large-French dual-lumen catheters in the right atrium, it would be of interest to obtain clinical data re-evaluating the 'dual-vein approach' with separate blood delivery via a tip-hole catheter in order to provide high-volume hemofiltration.

HYDROXYETHYL STARCH 130 KD/0.4 AND ALBUMIN IMPROVE CVVH BIOCOMPATIBILITY WHEREAS GELATIN AND HYDROXYETHYL STARCH 200 KD/0.5 LEAD TO ADVERSE SIDE EFFECTS OF CVVH IN ANESTHETIZED PIGS

Both fluid management and renal replacement therapies play a fundamental role in the treatment of critically ill patients. In a recent in vitro study, we have shown specific interactions of different colloids and the hemocompatibility of hemofilters. The present study was performed to compare the five most common fluids for volume resuscitation, i.e., normal saline (SAL), hydroxyethyl starch 130 kd/0.4 (HES130), hydroxyethyl starch 200 kd/0.5 (HES200), albumin (ALB), and gelatin (GEL) with respect to their interaction with continuous venovenous hemofiltration (CVVH) in anesthetized domestic pigs.

METHODS

Animals (n = 63) were allocated randomly to the fluid type and the respective subgroups, which were divided into control and CVVH groups (n = 6 ndash; 7 per group). Bolus infusion of group specific fluid was followed by a bolus of heparin and the initiation of hemofiltration in CVVH groups. Thereafter, fluids were infused at constant rates, and heparin application was adjusted to keep the activated clotting time at 200 to 250 s. Hemodynamics, airway pressures, pulmonary gas exchange, diuresis, creatinine clearance, and blood cell counts were investigated during the entire procedure (10 ndash; 12 hours).

RESULTS

Basics of in vivo effects of SAL, HES130, and ALB were not altered during CVVH. HES130 and ALB enabled stable hemocompatibility, diuresis, and hemodynamics in the respective groups. In contrast, organ functions were significantly different between control and CVVH groups when animals were treated with GEL or HES200. In particular, during CVVH, HES200 led to reduced platelet counts, deteriorated hemodynamics, and increasing airway pressures during CVVH. GEL led to increasing airway pressures, a decrease in pulmonary gas exchange, deteriorated hemodynamics, altered renal histomorphology, reduced platelet counts, and reduced hemoglobin.

CONCLUSIONS

Direct in vivo effects of colloids in anaesthetized and ventilated pigs are not predictable for their effects during CVVH. Interaction between CVVH and every volume substitute occur in a highly specific manner. This observation could be helpful to explain contradictory study results and should be considered for future study designs.