Effects of tourniquet number and exsanguination on amikacin concentrations in the radiocarpal and distal interphalangeal joints after low volume intravenous regional limb perfusion in horses

Pharmacokinetics of amikacin after intravenous, intra-articular, and combined intravenous and intra-articular administration in healthy neonatal foals

BACKGROUND

Pharmacokinetics of amikacin administered IV to neonatal foals are described, but little data are available regarding the plasma concentrations contributed by concurrent intra-articular (IA) administration.

HYPOTHESIS/OBJECTIVES

Compare the pharmacokinetics of amikacin when the total dose is administered IV compared to being divided between IV and IA routes of administration in neonatal foals and predict the plasma concentrations from various combined IV and IA dosing regimens.

ANIMALS

Eight healthy neonatal foals.

METHODS

Foals received 3 amikacin treatment protocols: (1) IV-only (25 mg/kg q24h IV), (2) concurrent IV and IA (16.7 mg/kg q24h IV and 8.3 mg/kg q24h into 1 tarsocrural joint), and (3) IA-only (8.3 mg/kg q24h into 1 tarsocrural joint). Protocols were administered for 3 days beginning at 7, 14, and 21 days of age. Plasma concentrations ≥53 μg/mL at 30 minutes were considered therapeutic for isolates with intermediate susceptibility.

RESULTS

Foal age was a significant variable. The IV-only protocol met or exceeded the 30-minute plasma concentrations considered therapeutic (mean μg/mL [95% confidence interval, CI]) in 7- to 9-day-old (54.0 [52.2-56.9]), 14- to 16-day-old (58.1 [55.2-61.0]), and 21- to 23-day-old (66.6 [63.7-69.6]) foals. Concurrent IV and IA protocol did not reach the 30-minute concentration considered therapeutic in 7- to 9-day-old foals (46.5 [43.6-49.4]) but did in 14- to 16-day-old (62.9 [60.0-65.8]) and 21-to 23-day-old (62.6 [59.7-65.6]) foals.

CONCLUSIONS AND CLINICAL IMPORTANCE

Concurrent IV and IA administration of amikacin produces 30-minute plasma concentrations considered therapeutic in foals 14 to 23 days old, but concentrations observed in younger foals might be below those considered therapeutic for isolates with intermediate susceptibility to amikacin.

Phenylbutazone concentrations in synovial fluid following administration via intravenous regional limb perfusion in the forelimbs of six adult horses

Background

Pain management is critical to equine welfare with non-steroidal anti-inflammatory drugs (NSAID) commonly used in horses. However, systemic NSAID use is limited by harmful gastrointestinal and renal side effects. Intravenous regional limb perfusion (IVRLP) is a technique used in horses that produces high, local antibiotic concentrations while limiting systemic circulation. NSAID-IVRLP would be a novel method of local pain management while limiting systemic NSAID side effects. To date, NSAID-IVRLP administration has not been reported in horses. This study aimed to identify the pharmacokinetics and local complications associated with using the NSAID phenylbutazone (PBZ) for IVRLP in six standing adult horses.

Methods

PBZ-IVRLP, at a dose of 2.2 mg/kg PBZ, was performed in a randomly assigned forelimb cephalic vein in 6 standing, healthy adult horses. A placebo-IVRLP was performed in the contralateral forelimb for comparison. Systemic serum and radiocarpal joint synovial fluid PBZ concentrations were identified at various timepoints (before IVRLP T-0 h, just after tourniquet removal T-0.5, 1.5, 3, 5, 12, 16, and 24 h post IVRLP) for non-compartmental pharmacokinetic analysis and concentration over time curves. Local complications associated with PBZ-IVRP were evaluated for up to 7 days following PBZ-IVRLP using physical and ultrasonographic assessment. On day 7 horses were humanely euthanized with histology performed on both forelimbs at PBZ-IVRLP and placebo-IVRLP administration sites.

Results

Non-compartmental pharmacokinetics for PBZ, and its major metabolite oxyphenbutazone (OBZ), were determined for serum and synovial fluid. Synovial PBZ concentrations (mean ± SD; 1.9 ± 2.1 μg/mL) were significantly lower (p = 0.03; CI,0.46-7.36) than serum PBZ concentrations (5.8 ± 5.1 μg/mL) at any time point. Physical and ultrasonographic measurements were not significantly different between PBZ- and placebo-IVRLP forelimbs. The most common histologic findings included focal deep dermal/subcutaneous hemorrhage and edema. Two horses showed perivasculitis and one horse showed a resolving thrombus in the cephalic vein of the PBZ-IVRLP limb. This horse also had severe perivasculitis and fibrinosuppurative dermatitis/panniculitis in the placebo-IVRLP limb.

Conclusion

PBZ-IVRLP pharmacokinetics at a 2.2 mg/kg dose showed no benefit compared to systemic PBZ administration in standing adult horses. Local complications associated with PBZ-IVRLP were similar to placebo-IVRLP on physical and ultrasonographic evaluation.

Regional antibiotic perfusion through the lateral saphenous vein in two horses with septic calcaneal osteitis

In this case report, two horses with chronic refractory infections in the tuber calcanei were successfully managed via intravenous antibiotic regional limb perfusion through the lateral saphenous vein after failure of conventional treatment approaches, including surgery and intravenous regional limb perfusion using the cranial branch of the medial saphenous vein. Surgical delay in these cases may have allowed the development of chronic infection, which prevented the conventional regional perfusion from working effectively. The spatial difference of the vessels relative to the tuber calcanei possibly contributed to the treatment outcome in these horses. This report describes a novel approach for regional antimicrobial perfusion to the equine plantar hock region using the lateral saphenous vein.

Effects of regional limb perfusion technique on concentrations of antibiotic achieved at the target site: A meta-analysis

Intravenous regional limb perfusions (RLP) are widely used in equine medicine to treat distal limb infections, including synovial sepsis. RLPs are generally deemed successful if the peak antibiotic concentration (Cmax) in the sampled synovial structure is at least 8–10 times the minimum inhibitory concentration (MIC) for the bacteria of interest. Despite extensive experimentation and widespread clinical use, the optimal technique for performing a successful perfusion remains unclear. The objective of this meta-analysis was to examine the effect of technique on synovial concentrations of antibiotic and to assess under which conditions Cmax:MIC ≥ 10. A literature search including the terms “horse”, “equine”, and “regional limb perfusion” between 1990 and 2021 was performed. Cmax (μg/ml) and measures of dispersion were extracted from studies and Cmax:MIC was calculated for sensitive and resistant bacteria. Variables included in the analysis included synovial structure sampled, antibiotic dose, tourniquet location, tourniquet duration, general anesthesia versus standing sedation, perfusate volume, tourniquet type, and the concurrent use of local analgesia. Mixed effects meta-regression was performed, and variables significantly associated with the outcome on univariable analysis were added to a multivariable meta-regression model in a step-wise manner. Sensitivity analyses were performed to assess the robustness of our findings. Thirty-six studies with 123 arms (permutations of dose, route, location and timing) were included. Cmax:MIC ranged from 1 to 348 for sensitive bacteria and 0.25 to 87 for resistant bacteria, with mean (SD) time to peak concentration (Tmax) of 29.0 (8.8) minutes. Meta-analyses generated summary values (θ) of 42.8 x MIC and 10.7 x MIC for susceptible and resistant bacteria, respectively, though because of high heterogeneity among studies (I² = 98.8), these summary variables were not considered reliable. Meta-regression showed that the only variables for which there were statistically significant differences in outcome were the type of tourniquet and the concurrent use of local analgesia: perfusions performed with a wide rubber tourniquet and perfusions performed with the addition of local analgesia achieved significantly greater concentrations of antibiotic. The majority of arms achieved Cmax:MIC ≥ 10 for sensitive bacteria but not resistant bacteria. Our results suggest that wide rubber tourniquets and concurrent local analgesia should be strongly considered for use in RLP and that adequate therapeutic concentrations (Cmax:MIC ≥ 10) are often achieved across a variety of techniques for susceptible but not resistant pathogens.

Effect of perfusate volume on amikacin concentrations after saphenous intravenous regional limb perfusion in standing, sedated horses

OBJECTIVE

To determine the influence of perfusate volume on synovial fluid amikacin concentrations in the joints of the hind limb after standing saphenous intravenous regional limb perfusion (IVRLP).

STUDY DESIGN

Randomized crossover design.

ANIMALS

Six adult horses.

METHODS

Saphenous IVRLP was performed in 6 standing horses with 1 g of amikacin diluted with 0.9% NaCl to volumes of 10 ml, 60 ml, and 120 ml. Samples of synovial fluid from the tarsocrural, metatarsophalangeal, and hind limb distal interphalangeal joints were collected at 15 and 30 min after perfusate administration. Concentrations of 40 μg/ml and 160 μg/ml were considered therapeutic for susceptible and resistant pathogens, respectively.

RESULTS

No difference in synovial fluid amikacin concentrations was detected between volumes in any joint (P = .4). All synovial fluid amikacin concentrations were higher at 30 min compared to 15 min (P = .003). All median synovial fluid amikacin concentrations at 30 min were > 40 μg/ml using the 60 ml and 120 ml volumes. Synovial fluid amikacin concentrations >40 μg/ml were only reached in the hind limb distal interphalangeal joint when the 10 ml volume was used. All median synovial fluid amikacin concentrations observed were < 160 μg/ml.

CONCLUSIONS

Target concentrations for pathogens that were considered susceptible were consistently reached with perfusate volumes of 60 ml and 120 ml. However, median synovial fluid amikacin concentrations did not reach target levels for resistant pathogens.

CLINICAL SIGNIFICANCE

Perfusate volumes of 60 ml or 120 ml are recommended to treat infections due to susceptible pathogens in the joints of the distal hind limb. These results justify investigation of saphenous IVRLP with different perfusate volumes using higher doses of amikacin.

Increasing tourniquet number has no effect on amikacin concentration within the radiocarpal joint in horses undergoing intravenous regional limb perfusion

OBJECTIVE

To determine whether IV regional limb perfusion (IVRLP) performed in the cephalic vein with a wide rubber tourniquet (WRT) applied proximal and distal to the carpus results in a higher peak concentration (Cmax) of amikacin in the radiocarpal joint (RCJ), compared with the Cmax for IVRLP using a single WRT proximal to the carpus.

Animals

7 healthy adult horses.

Procedures

Horses underwent IVRLP using standing sedation with 2 g of amikacin sulfate diluted to 60 mL by use of saline (0.9% NaCl) solution in the cephalic vein with 2 different tourniquet techniques; proximal WRT (P) and proximal and distal WRT (PD). Synovial fluid was collected from the RCJ at 5, 10, 15, 20, 25, and 30 minutes after IVRLP. Tourniquets were removed after the 30-minute sample was collected. Blood samples from the jugular vein were collected at 5, 10, 15, 20, 25, 29, and 31 minutes after IVRLP. Amikacin concentration was quantified by a fluorescence polarization immunoassay. Median peak concentration (Cmax) of amikacin and time to maximum drug concentration (Tmax) within the RCJ were determined.

Results

Median peak concentration in the RCJ was 1331.4 μg/mL with technique P and 683.1 μg/mL with technique PD. Median Tmax occurred at 30 minutes with technique P and 25 minutes with technique PD. No significant (Cmax, P = 0.18; Tmax, P = 0.6) difference in amikacin Cmax or Tmax between techniques was detected.

Clinical Relevance

Placement of 2 WRTs offers no advantage to a single proximal WRT when performing IVRLP to deliver maximal amikacin concentrations to the RCJ using IVRLP.

Intravenous Regional Limb Perfusion in Standing and Recumbent Horses: A Comparative Radiographic Study

Although pharmacokinetic studies of drugs administered by intravenous regional limb perfusion (IRLP) to treat equine orthopedic infections suggest efficient drug distribution in the limbs, it remains unclear whether drug perfusion is affected by the position of the horse during the procedure. This study compared the perfusion of a radiopaque contrast into tissues of the extremities of horses maintained in standing and recumbent positions during an IRLP. Radiopaque contrast was administered through IRLP into the cephalic vein of 10 healthy adult horses under general anesthesia and right lateral recumbency (RG) or under sedation and standing (SG). The same animals were used in both groups, respecting a two-week washout period. Sequential radiographic images were performed immediately at the beginning of contrast administration (T0) and after 10, 20, 30, 40, and 50 minutes. Tourniquets were removed after 30 minutes. The time required for the contrast to reach the hooves was compared between groups. Contrast reached the hooves faster in SG (114 ± 15 seconds) compared with RG (236 ± 29 seconds) (P < 0.5). SG showed more uniform perfusion of the limb vessels, whereas RG showed more deposition of the contrast in the lateral digital vein, with smaller amounts reaching the hooves. From T10 onward, soft tissue radiopacity increased, albeit more markedly in standing than in recumbent animals, remaining until T50. Contrast radiography evidenced that IRLP performed in standing position leads to a quicker and more uniform perfusion of the vasculature and a more noticeable diffusion to the tissues than in recumbent horses.

Time to Peak Concentration of Amikacin in the Antebrachiocarpal Joint Following Cephalic Intravenous Regional Limb Perfusion in Standing Horses

OBJECTIVE

 The aim of this study was to determine the time (T_max) to the maximum concentration (C_max) of amikacin sulphate in synovial fluid of the radiocarpal joint (RCJ) following cephalic intravenous regional limb perfusion (IVRLP) using 2 g of amikacin sulphate.

METHODS

 Cephalic IVRLP was performed with 2 g of amikacin sulphate diluted in 0.9% NaCl to a total volume of 100 mL in six healthy adult mixed breed mares. An Esmarch's rubber tourniquet was applied for 30 minutes and the antibiotic solution was infused through a 23-gauge butterfly catheter. Synovial fluid was collected from the RCJ prior to the infusion and at 5, 10, 15, 20, 25 and 30 minutes after completion of IVRLP. The tourniquet was removed after the last arthrocentesis. Synovial fluid amikacin sulphate concentrations were determined by liquid chromatography/tandem mass spectrometry.

RESULTS

 The calculated mean T_max occurred at 15 minutes (range: 10-20 minutes) post-perfusion. The highest synovial fluid amikacin sulphate concentration was noted at 10 minutes in 2 horses, 15 minutes in 2 horses and 20 minutes in 2 horses. The highest mean concentration was 1023 µg/mL and was noted at 20 minutes. Synovial mean concentrations were significantly different between 15 and 30 minutes.

CLINICAL SIGNIFICANCE

 In this study no T_max occurred after 20 minutes; thus, 30 minutes of tourniquet application time appear to be excessive. The 20 minutes duration of tourniquet application appears sufficient for the treatment of the RCJ in cephalic IVRLP using 2 g amikacin sulphate in a total volume of 100 mL.

Synovial butorphanol concentrations and mechanical nociceptive thresholds after intravenous regional limb perfusion in standing sedated horses

OBJECTIVE

To determine synovial butorphanol concentrations and mechanical nociceptive threshold (MNT) changes after butorphanol intravenous regional limb perfusion (IVRLP).

STUDY DESIGN

Experimental ANIMALS: Six adult horses.

METHODS

Cephalic IVRLP was performed with 10 mg butorphanol in sedated horses with a wide rubber tourniquet and a total volume of 30 mL. Radiocarpal synovial fluid and serum concentrations along with MNT were evaluated prior to and 0.5, 1, 2, 4, and 6 hours after IVRLP. Butorphanol concentrations were determined with liquid chromatography coupled to tandem mass spectrometry positive electrospray ionization.

RESULTS

Butorphanol concentrations reached mean (SD) peak concentrations of 9.47 ng/mL (±12.00) in synovial fluid and 3.89 ng/mL (3.29) in serum 30 minutes after IVRLP. Concentrations remained above baseline for 4 hours in synovial fluid (P ≤ .017) and for 2 hours in serum (P ≤ .016). The only difference in MNT was detected 1 hour after IVRLP, when MNT were higher in controls than in treated horses (P = .047).

CONCLUSION

Butorphanol IVRLP seemed well tolerated and resulted in measurable levels of butorphanol in the radiocarpal synovial fluid of five of six horses.

CLINICAL SIGNIFICANCE

Intravenous regional limb perfusion appears to be a viable alternative to administer butorphanol, but additional investigation is required to evaluate the dose and local concentrations required for analgesia.

Subtourniquet pressures generated by application of wide-rubber tourniquets in standing, sedated horses

OBJECTIVE

To determine the influence of location and movement on subtourniquet pressure (STP) generated by application of a wide-rubber tourniquet (WRT) on equine limbs.

STUDY DESIGN

Randomized experimental cross-over design.

ANIMALS

Six standing, sedated horses.

METHODS

Horses were sedated with detomidine hydrochloride (0.2 μg/kg IV), and 4 investigators applied WRTs to the antebrachium (AB), gaskin (GK), and midmetacarpus (MC) of each horse in a predetermined, randomized order. Subtourniquet pressure was consequently measured at 10-minute intervals (T0, T10, T20, T30) for 30 minutes. Indirect systolic blood pressure (SBP) was measured presedation, postsedation, and throughout the tourniquet application period. Target STP was established as SBP + 100 mm Hg. Limb movements at each location were classified as none, low, moderate, or high, on the basis of counts and magnitude.

RESULTS

Mean STP did not change with time (P = .93) and exceeded SBP by 163 mm Hg (95% CI 122-205), 185 mm Hg (95% CI 156-214), and 402 mm Hg (95% CI 351-454) at the AB, GK, and MC, respectively. Mean STP at each location exceeded the target STP in 59 of 70 (81%) of the trials. Limb movements affected STP generated by tourniquets at the AB (P = .04) and MC (P < .0001) but not at the GK (P = .67).

CONCLUSION

Wide-rubber tourniquets applied at the AB, GK, and MC generated STP >100 mm Hg above SBP for 30 minutes in standing, sedated horses.

CLINICAL SIGNIFICANCE

Wide-rubber tourniquets as applied in this study can achieve and maintain the current recommended STP (SBP + 100 mm Hg) for equine IV regional limb perfusion. Number and magnitude of limb movement can decrease STP over time, potentially reducing the efficacy of a WRT.