Comparison of intraosseous or intravenous infusion for delivery of amikacin sulfate to the tibiotarsal joint of horses

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.

A Descriptive Study of the Clinical Presentation, Management, and Outcome of Horses with Acute Soft Tissue Trauma of the Tarsus and the Association with Synovial Involvement

Simple Summary

The hock is commonly involved in traumatic injuries in horses and due to the large number of synovial structures located in the region, this frequently results in synovial infection which is a major and potentially life-threatening complication in horses. The aim of this retrospective study was to describe the clinical presentation, diagnostic procedures, management, and outcome of cases with acute soft tissue trauma to the hock and to identify the clinical features that were associated with synovial infection in these cases. This study found that increased synovial effusion, severe lameness on admission, and the persistence of lameness as well as certain wound locations were more commonly associated with a diagnosis of synovial infection. Advanced diagnostic modalities such as radiographs, ultrasonography, and measurements of inflammatory markers aided in establishing the correct diagnosis. The duration of systemic antimicrobial treatment was shorter than previously reported and many cases received local antimicrobial treatment at the site of injury, which may have improved its efficacy. At the time of discharge, while lameness was still present in some cases, the overall survival was excellent. This study describes the clinical features and treatment of these commonly encountered injuries, and this knowledge may benefit clinicians in the future.

Abstract

The tarsus is one of the most common areas of traumatic injury with associated synovial involvement (SI) in horses. The aim of this retrospective study was to describe the clinical presentation, diagnostic procedures, management (emphasizing the type, duration, and route of antimicrobial administration), and outcome of cases with acute soft tissue trauma to the tarsal region. The presenting clinical features, the results of diagnostic modalities, and the initial response to therapy were assessed for their usefulness to predict SI. Medical records of 72 cases were included and SI was diagnosed in 34 cases (47.2%). Increased synovial effusion, lameness on admission (OR = 4.1; 95%CI 1.0–16.4), persistent lameness (OR = 5.7; 95%CI 1.8–17.9), increased blood SAA values (≥200 mg/L) from initial to second measurement (OR = 4.3; 95%CI 1.2–15.5), and wound location on the plantar/plantarolateral/plantaromedial compared to the lateral aspect of the tarsus (OR = 7.0; 95%CI 1.6–30.9) were associated with SI. Radiographs, ultrasonography, and the use of pressure testing when a wound was present proved to be useful in correctly diagnosing SI. The median duration of systemic antimicrobial administration was 8 (IQR: 5 to 9) days and most horses received local antimicrobial therapy. This study highlights several relevant clinical features and their association with SI and emphasizes the usefulness of local antimicrobial therapy in these cases.

Evaluation of totally implantable catheters in healthy horses

BACKGROUND

For horses requiring prolonged daily cephalic intravenous regional limb perfusion (IVRLP), the use of a totally implantable catheter (TIC) could be indicated to reduce complications associated with frequent venipuncture or external catheterization. This study aims to evaluate the implantation technique of the TIC in the cephalic vein of horses for IVRLP, describe the complications associated with the device's placement and use, and assess its viability up to 60 days after implantation. Totally implantable catheters, cut to 15 cm (n = 5) and 46 cm (n = 5) in length, were implanted into one cephalic vein in ten adult horses (n = 10). Twenty-four hours following placement, IVRLP with contrast was performed via the TIC and evaluated with radiography. Physical examinations, lameness evaluation, hematologic assessment, and the catheter patency tests were performed at scheduled intervals for the duration of catheterization (7-60 days).

RESULTS

Catheters were implanted without difficulty and allowed for IVRLP 24 h post implantation. Complications resulted in removal of the catheters, with four maintained for 7 days, three in place for 15 days, and three catheters maintained for 60 days. Complications included lameness, limb swelling, catheter kinking, and venous thrombosis.

CONCLUSIONS

The implantation technique of the TIC in the cephalic vein of horses is feasible and requires minimal technical effort. Although TIC allows venous access without the need for repeated venipuncture, its long-term use presents complications. For horses requiring prolonged daily cephalic IVRLP, the use of a TIC could be indicated. However, the high incidence of venous thrombosis may limit clinical application.

Synovial Concentration of Trimethoprim-Sulphadiazine Following Regional Limb Perfusion in Standing Horses

Simple Summary

Trimethoprim-sulphadiazine is a first line antimicrobial drug recommended for use in equine orthopedic infections such as deep wounds, ulcerative lymphangitis and septic arthritis. The pharmacokinetics of trimethoprim-sulphadiazine, when delivered through intravenous regional limb perfusion, has not been previously described. This study aimed at describing the pharmacokinetics and safety of the administration of trimethoprim-sulphadiazine through a single cephalic vein injection. Several horses in the study suffered from severe vasculitis, and the resulting synovial fluid concentration of trimethoprim-sulphadiazine over time was low. In light of these findings, the administration of trimethoprim-sulphadiazine to horses using regional limb perfusion via cephalic appears unwarranted.

Abstract

The aim of this study was to investigate the safety and pharmacokinetics of trimethoprim-sulphadiazine administered via intravenous regional limb perfusion (IVRLP) into the cephalic vein. According to the hypothesis, the drug could be administered without adverse effects and the synovial concentrations would remain above the minimum inhibitory concentration (MIC) for trimethoprim-sulphadiazine (0.5 and 9.5 µg/mL) for 24 h. Ten (n = 10) horses underwent cephalic vein IVRLP with an Esmarch tourniquet applied for 30 min. Four grams (4 g) of trimethoprim-sulphadiazine (TMP-SDZ) were diluted at 0.9% NaCl for a total volume of 100 mL. Synovial fluid and blood samples were obtained immediately before IVRLP and at 0.25, 0.5, 2, 6, 12 and 24 h after the initiation of IVRLP. Trimethoprim and sulphadiazine concentrations were determined using a method based on liquid chromatography/tandem mass spectrometry. The C_max (peak drug concentration) values were 36 ± 31.1 and 275.3 ± 214.4 µg/mL (TMP and SDZ). The respective t_max (time to reach C_max) values were 20 ± 7.8 and 26.4 ± 7.2 min. The initial synovial fluid concentrations were high but decreased quickly. No horse had synovial concentrations of trimethoprim-sulphadiazine above the MIC at 12 h. Severe vasculitis and pain shortly after IVRLP, lasting up to one week post-injection, occurred in five out of 10 horses. In conclusion, IVRLP with trimethoprim-sulphadiazine cannot be recommended due to the low concentrations of synovial fluid over time and the frequent severe adverse effects causing pain and discomfort in treated horses. Thus, in cases of septic synovitis with bacteria sensitive to trimethoprim-sulphadiazine, other routes of administration should be considered.

Time required to achieve maximum amikacin concentration in the synovial fluid of the tarsocrural joint following administration of the drug by intravenous regional limb perfusion in horses

OBJECTIVE

To determine the median time to maximum concentration (t_max) of amikacin in the synovial fluid of the tarsocrural joint following IV regional limb perfusion (IVRLP) of the drug in a saphenous vein of horses.

ANIMALS

7 healthy adult horses.

PROCEDURES

With each horse sedated and restrained in a standing position, a 10-cm-wide Esmarch tourniquet was applied to a randomly selected hind limb 10 cm proximal to the point of the tarsus. Amikacin sulfate (2 g diluted with saline [0.9% NaCl] solution to a volume of 60 mL) was instilled in the saphenous vein over 3 minutes with a peristaltic pump. Tarsocrural synovial fluid samples were collected at 5, 10, 15, 20, 25, and 30 minutes after completion of IVRLP. The tourniquet was removed after collection of the last sample. Amikacin concentration was quantified by a fluorescence polarization immunoassay. Median maximum amikacin concentration and t_max were determined.

RESULTS

1 horse was excluded from analysis because an insufficient volume of synovial fluid for evaluation was obtained at multiple times. The median maximum synovial fluid amikacin concentration was 450.5 μg/mL (range, 304.7 to 930.7 μg/mL), and median t_max was 25 minutes (range, 20 to 30 minutes). All horses had synovial fluid amikacin concentrations ≥ 160 μg/mL (therapeutic concentration for common equine pathogens) at 20 minutes after IVRLP.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that, in healthy horses, maintaining the tourniquet for 20 minutes after IVRLP of amikacin in a saphenous vein was sufficient to achieve therapeutic concentrations of amikacin in the tarsocrural joint.

Comparison of plasma and intra-articular gentamicin levels after intravenous administration in healthy horses

Septic arthritis is considered one of the most severe disorders that affect horses’ joints. Therapy is intended to eliminate the microorganisms that cause this infection. The intravenous administration of antibiotics is an easily performed technique, but there is no guarantee that the antibiotics will reach the joint milieu at high concentrations and remain elevated for a certain period of time. This study aimed to determine and compare the levels of gentamicin in the plasma and synovial fluid of healthy horses after intravenous administration for seven days. Five horses received 6.6 mg/kg intravenous gentamicin every 24 h for seven consecutive days. Blood and synovial fluid samples were collected from the right metacarpal-phalangeal joint before the start of the treatment (T0) and after 6 h (T6), 12 h (T12), and every 24 h during antibiotic therapy for seven days (D1 to D7). The levels of gentamicin in serum and synovial fluid were quantified by Enzyme-Linked Immunosorbent Assay (ELISA). The intravenous administration of 6.6 mg/kg of gentamicin, in horses, after a period of 24 h, promotes synovial fluid concentrations below the MIC of the drug, in spite of reaching high plasma concentrations of gentamicin, daily mean serum concentration which was 29-fold higher than the minimum inhibitory concentration (MIC) of the drug. The intravenous administration every 24 h during seven consecutive days did not cause systemic side effects, such as hepatic or renal injury.

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.

Intravenous and intraosseous regional limb perfusion of ceftiofur sodium in an avian model

OBJECTIVE

To assess whether IV regional limb perfusion (IVRLP) and intraosseous regional limb perfusion (IORLP) of ceftiofur sodium resulted in clinically relevant drug concentrations in the synovial fluid of the tibiotarsal-tarsometatarsal joint of chickens (ie, an avian model) and to determine whether one of those techniques was superior to the other.

ANIMALS

12 healthy adult hens.

PROCEDURES

Birds were randomly assigned to receive ceftiofur sodium (2 mg/kg) by the IVRLP (n = 4), IORLP (4), or IM (control; 4) route once daily for 6 consecutive days. Blood and tibiotarsal-tarsometatarsal synovial fluid samples were collected 15 minutes after ceftiofur administration on predetermined days for quantification of ceftiofur concentration. Plasma and synovial fluid ceftiofur concentrations were compared among the 3 groups.

RESULTS

All 4 birds in the IVRLP group developed mild to moderate bruising around the injection site, but this bruising did not prohibit completion of the prescribed treatment regimen. No adverse effects were observed in any of the other birds. The mean plasma and synovial fluid ceftiofur concentrations exceeded the therapeutic threshold for most common bacterial pathogens (> 1.0 μg/mL) at all sample acquisition times for all 3 groups. The mean synovial fluid ceftiofur concentration for the IVRLP group was significantly greater than that for the IORLP and control groups at all sample acquisition times.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that IVRLP may be a safe and effective technique for antimicrobial administration to birds with joint infections, contaminated wounds, pododermatitis, and other musculoskeletal infections of the distal aspect of a limb.

Surgical site infection associated with equine orthopedic internal fixation: 155 cases (2008-2016)

OBJECTIVE

To determine the prevalence of surgical site infection (SSI) after internal fixation and to identify risk factors for SSI and nonsurvival.

STUDY DESIGN

Retrospective study.

ANIMALS

One hundred fifty-five horses with long bone fractures or arthrodesis treated by internal fixation at 1 hospital between 2008-2016.

METHODS

Signalment, diagnosis, surgical repair, surgeon, surgical time, antimicrobial use, SSI onset, bacterial identification, and adjunct treatments were recorded. Perioperative variables were analyzed to identify risk factors associated with outcomes.

RESULTS

Surgical-site infection was reported in 22 of 155 (14.2%) horses, which is lower than what has been previously reported (P = .003). Horses with fetlock arthrodesis or ulnar fracture were more likely to develop SSI. Local prophylactic antimicrobial therapy was associated with an increased risk of SSI. Horses with SSI were 12 times (P < .0001) less likely to survive to discharge than horses without SSI. Horses with a fetlock or carpal arthrodesis or those with radial/humeral/femoral fractures were less likely to survive. No association was identified between open fractures, open reduction and internal fixation, or surgical times and SSI.

CONCLUSION

The prevalence of SSI in this population was lower than what has been previously reported. Horses with fetlock or carpal arthrodesis or radial/humeral/femoral fractures were at increased risk for SSI and/or nonsurvival to discharge. A protective role of local antimicrobial therapy for SSI could not be established.

CLINICAL RELEVANCE

The impact of SSI on outcomes of cases of equine internal fixation remains substantial. Identification of cases at higher risk of SSI should influence surgical technique, postoperative management, and early intervention when SSI is suspected. Additional investigation is warranted regarding local antimicrobial therapy.

The John N. Insall Award: Higher Tissue Concentrations of Vancomycin Achieved With Intraosseous Regional Prophylaxis in Revision TKA: A Randomized Controlled Trial

BACKGROUND

In primary TKA, prophylaxis with low-dose vancomycin through intraosseous regional administration (IORA) achieves tissue concentrations six to 10 times higher than systemic administration and was shown to provide more effective prophylaxis in an animal model. However, in revision TKA, the presence of a tibial implant may compromise IORA injection, and tourniquet deflation during a prolonged procedure may lower tissue concentrations.

QUESTIONS/PURPOSES

(1) Does low-dose IORA reliably provide equal or higher tissue concentrations of vancomycin compared with systemic IV administration in revision TKA? (2) Are tissue concentrations of vancomycin after IORA maintained for the duration of the revision TKA despite a period of tourniquet deflation? (3) Is there any difference in early postoperative (< 6 weeks) complications between IORA and systemic IV administration in revision TKA?

METHODS

Twenty patients undergoing aseptic revision TKA were randomized to two groups. The IV group received 1 g systemic IV prophylactic vancomycin. The IORA group received 500 mg vancomycin as a bolus injection into a tibial intraosseous cannula below an inflated thigh tourniquet before skin incision. In all patients receiving IORA, intraosseous tibial injection was technically possible despite the presence of a tibial implant. Mean procedure length was 3.5 hours in both groups. Mean initial tourniquet inflation was 1.5 hours with a second inflation for a mean of 35 minutes during cementation. During the procedure, subcutaneous fat and bone samples were taken at regular intervals. Tissue vancomycin concentrations were measured using high-performance liquid chromatography.

RESULTS

Overall geometric mean tissue concentration of vancomycin in fat samples was 3.7 μg/g (95% confidence interval [CI], 2.6-5.2) in the IV group versus 49.3 μg/g in the IORA group (95% CI, 33.2-73.4; ratio between means 13.5; 95% CI, 8.2-22.0; p < 0.001); mean tissue concentrations in femoral bone were 6.4 μg/g (95% CI, 4.5-9.2) in the IV group versus 77.1 μg/g (95% CI, 42.4-140) in the IORA group (ratio between means 12.0; 95% CI, 6.2-23.2; p < 0.001). Vancomycin concentrations in the final subcutaneous fat sample taken before closure were 5.3 times higher in the IORA group versus the IV group (mean ± SD, 18.2 ± 11.6 μg/g IORA versus 3.6 ± 2.5 μg/g; p < 0.001). The intraarticular concentration of vancomycin on postoperative Day 1 drain samples was not different between the two groups with the numbers available (mean 4.6 μg/L in the IV group versus 6.6 μg/g in the IORA group; mean difference 2.0 μg/g; 95% CI, 6.2-23.2; p = 0.08).

CONCLUSIONS

IORA administration of vancomycin in patients undergoing revision TKA resulted in tissue concentrations of vancomycin five to 20 times higher than systemic IV administration despite the lower dose. High tissue concentrations were maintained throughout the procedure despite a period of tourniquet deflation. These preliminary results justify prospective cohort studies, which might focus on broader safety endpoints in more diverse patient populations. We believe that these studies should evaluate patients undergoing revision TKA in particular, because the risk of infection is greater than in patients undergoing primary TKA.

LEVEL OF EVIDENCE

Level I, therapeutic study.

SUCCESSFUL TREATMENT OF DIGITAL OSTEITIS BY INTRAVENOUS REGIONAL PERFUSION OF CEFTIOFUR IN AN AFRICAN ELEPHANT (LOXODONTA AFRICANA)

A 41-yr-old African elephant ( Loxodonta africana ) presented with a swollen third digit of the left forelimb and a 2-cm hole in the pad. Corrective trimming, topical treatments, and an oral antibiotic resulted in apparent resolution; however, it reoccurred after 4 mo. Radiographs suggested bone lysis in the third phalanx, with the primary differential diagnosis being septic osteitis. Flushing with metronidazole solution and intravenous regional perfusion (IVRP) of the foot were commenced. A tourniquet was applied just above the carpus, an interdigital vein was identified by ultrasound, and into this vein 2 g (20 ml) of ceftiofur sodium solution, followed by 60 ml of heparinized saline, was administered. The foot was kept raised for 25 min and then the tourniquet was removed. IVRP was repeated every other day for 70 treatments over 6 mo. Healing occurred, which was confirmed radiographically. IVRP offers an excellent treatment modality in a well-trained elephant.

The Effect of Perfusate Volume on Amikacin Concentration in the Metacarpophalangeal Joint Following Cephalic Regional Limb Perfusion in Standing Horses

OBJECTIVE

To determine the influence of 3 perfusate volumes on amikacin concentration in the metacarpophalangeal joint following cephalic regional limb perfusion (RLP) in standing horses.

ANIMALS

Seven healthy horses.

METHODS

Three perfusate volumes (100, 60, and 30 mL), containing 2 grams of amikacin, were tested during intravenous RLP at the cephalic vein, placing the tourniquet at mid antebrachium, in standing sedated horses. Synovial fluid was collected from the metacarpophalangeal joint before perfusion and at 30 and 120 minutes after perfusion. Serum samples were taken from the jugular vein at the same time points. Samples were analyzed for amikacin concentrations and a repeated measures ANOVA, followed by least squares difference pairwise comparisons to identify differences in amikacin concentration across perfusate volumes. Differences were considered significant at P<.05.

RESULTS

The mean amikacin concentration in synovial fluid at 30 minutes after perfusion was significantly higher following perfusate volume of 100 mL (579 μg/mL), compared to volumes of 60 mL (227 μg/mL) or 30 mL (282 μg/mL) (P<.05). When a threshold of 160 μg/mL was used, more horses reached the synovial therapeutic threshold following perfusate volume of 100 mL (100%), than horses receiving 60 mL (43%) and 30 mL (57%) at 30 minutes after injection.

CONCLUSION

The use of 100 mL volume for RLP at the cephalic vein in standing horses resulted in higher concentration of amikacin in the synovial fluid and is recommended for use in clinical cases.

Evaluation of intravenous regional perfusion with amphotericin B and dimethylsulfoxide to treat horses for pythiosis of a limb

BACKGROUND

Treatment for horses with pythiosis of a limb is challenging. This study aims to evaluate the effects of administering amphotericin B in a 10 % solution of dimethylsulfoxide by intravenous regional limb perfusion (IRLP) to treat horses for cutaneous pythiosis of a limb.

RESULTS

All 15 of the horses treated had complete resolutions of their lesion between 6 to 9 weeks after a single IRLP treatment. No complications were observed at the site of venipuncture for IRLP. Before initiation of treatment, there was anemia and marked leucocytosis which resolved following treatment. Serum biochemistry showed no significant changes.

CONCLUSIONS

IRLP administration of amphotericin B in a 10 % DMSO solution was easily performed, relatively inexpensive and an effective treatment for treating horses for pythiosis of a limb and resolved the infection with no complications.

Evaluation of regional limb perfusion with chloramphenicol using the saphenous or cephalic vein in standing horses

Regional limb perfusion (RLP) significantly decreases morbidity and mortality associated with distal limb injuries in horses. There is an urgent need for finding additional effective antimicrobial drugs for use in RLP. In this study, we tested the pharmacokinetics (PK) of chloramphenicol in RLP. Eight horses participated in the study, which was approved by the University Animal Care and Use Committee. The cephalic and the saphenous veins were used to perfuse the limbs. Synovial samples were collected from the metacarpo/metatarsophalangeal (MCP/MTP) joint. The Friedman Test was applied for assessing change in PK concentration over time, for all time points. The Wilcoxon Signed Ranks Test was used to test the difference between PK concentration in joint & serum as well as concentration in joint vs. MIC. The comparison of measurements between measurements taken on hind vs. front legs was carried out using the Mann-Whitney Test. A P-value of 5% or less was considered statistically significant. After RLP, the concentration of chloramphenicol in the synovial fluid of the MCP/MTP joint using either the cephalic or the saphenous vein was initially far above the minimal inhibitory concentration (MIC) of most susceptible pathogens and remained above the MIC for approximately 6 h. The results indicate that performing RLP using the cephalic and saphenous veins enables reaching concentrations of chloramphenicol in the MCP/MTP joint that are well above the MIC of most susceptible pathogens. The chloramphenicol concentrations achieved in the synovial fluid of the MCP/MTP joint in the current study were between 1.5 (MTP) and 7 (MCP) times the MIC of MRSA in horses. These results are encouraging since MRSA infections are becoming far more common, causing considerable morbidity. To the best of our knowledge, this is the first study to evaluate the pharmacokinetics of chloramphenicol following RLP in the horse and the results are positive.

The Mark Coventry Award: Higher tissue concentrations of vancomycin with low-dose intraosseous regional versus systemic prophylaxis in TKA: a randomized trial

BACKGROUND

In response to increasing antibiotic resistance, vancomycin has been proposed as an alternative prophylactic agent in TKA. However, vancomycin requires a prolonged administration time, risks promoting further antibiotic resistance, and can cause systemic toxicity. Intraosseous regional administration (IORA) is known to achieve markedly higher antibiotic concentrations than systemic administration and may allow the use of a lower vancomycin dose.

QUESTIONS/PURPOSES

We assessed whether low-dose IORA vancomycin can achieve tissue concentrations equal or superior to those of systemic administration in TKA and compared complications between patients treated with IORA and intravenous vancomycin.

METHODS

We randomized 30 patients undergoing primary TKA to receive 250 or 500 mg vancomycin via IORA or 1 g via systemic administration. IORA was performed as a bolus injection into a tibial intraosseous cannula below an inflated thigh tourniquet immediately before skin incision. Subcutaneous fat and bone samples were taken during the procedure and antibiotic concentrations measured.

RESULTS

The overall mean tissue concentration of vancomycin in subcutaneous fat was 14 μg/g in the 250-mg IORA group, 44 μg/g in the 500-mg IORA group, and 3.2 μg/g in the systemic group. Mean concentrations in bone were 16 μg/g in the 250-mg IORA group, 38 μg/g in the 500-mg IORA group, and 4.0 μg/g in the systemic group. One patient in the systemic group developed red man syndrome during infusion.

CONCLUSIONS

Low-dose IORA vancomycin results in tissue concentrations equal or superior to those of systemic administration. IORA optimizes timing of vancomycin administration, and the lower dose may reduce the risk of systemic side effects while providing equal or enhanced prophylaxis in TKA.

Clinical and pharmacokinetic effects of regional or general anaesthesia on intravenous regional limb perfusion with amikacin in horses

REASONS FOR PERFORMING STUDY

Antimicrobial i.v. regional limb perfusion (IV-RLP) is clinically performed on anaesthetised or sedated horses with or without regional anaesthesia. To date, no scientific data are available on the clinical and pharmacokinetic effects of these anaesthetic protocols on antimicrobial IV-RLP, which is believed to result in better tourniquet efficiency due to decreased movement.

OBJECTIVE

To determine the effects of regional or general anaesthesia on the clinical and synovial pharmacokinetic parameters of amikacin administered by IV-RLP to horses.

STUDY DESIGN

Experimental crossover study.

METHODS

Eight healthy horses received 4 treatments of amikacin IV-RLP in a randomised, blinded, crossover design: standing sedation without regional anaesthesia (CNT); standing sedation with i.v. regional anaesthesia; standing sedation with perineural regional anaesthesia (PNA); or general anaesthesia. Synovial fluid amikacin concentrations were measured over 24 h and regional pharmacokinetic parameters calculated. Heart and respiratory rates, visual analogue scale of discomfort, number of times the limb was lifted and number of additional sedations administered were recorded. Analysis of variance crossover analysis was applied with significance level at P < 0.05.

RESULTS

Amikacin concentrations and regional pharmacokinetic parameters did not differ significantly among treatments. Visual analogue scores (mean ± s.d.) were significantly lower with PNA (19 ± 15) vs. i.v. regional anaesthesia (69 ± 36) or CNT (81 ± 13; P < 0.001). Significantly less lifting of the limb (mean ± s.d.) occurred with PNA (20 ± 20) vs. CNT (54 ± 22; P < 0.04).

CONCLUSIONS

Perineural regional anaesthesia before IV-RLP was most effective in providing comfort to standing, sedated horses without significantly affecting the regional pharmacokinetic parameters of amikacin. High variability of synovial amikacin concentrations was present. The use of general anaesthesia for IV-RLP is not justified based on this study.

Surgical treatment of distal tarsal joint luxations in three horses

The clinical signs, radiographic findings, surgical treatment, and outcome of three horses with luxation of the distal tarsal joints are reported. Two patients showed luxations of the tarsometatarsal joint whereas luxation of the proximal intertarsal joint was found in one case. Open reduction, followed by internal fixation was performed in two horses and closed reduction with a transfixation pin cast was performed in the third. The treatment in all three cases resulted in a satisfactory clinical outcome.

Clinical use of antimicrobial regional limb perfusion in horses: 174 cases (1999-2009)

OBJECTIVE

To describe the clinical use of regional limb perfusion with antimicrobials (A-RLP), complications, and outcome in a large series of patients.

DESIGN

Retrospective case series.

ANIMALS

174 horses.

PROCEDURES

Medical records of horses treated with A-RLP between 1999 and 2009 were reviewed. Signalment, primary complaint, horse use, etiology, duration of clinical signs, previous treatment, structures involved, concurrent conditions, A-RLP characteristics, additional treatments, complications, and outcome were recorded. At long-term follow-up, 2 outcomes were investigated: survival rate and return to previous use at the same or higher level. Univariate and multivariate logistic regression analyses were conducted.

RESULTS

Group 1 (96 horses) included septic synovitis. Group 2 (50 horses) included extrasynovial lacerations (23 horses) and fresh, minimally contaminated intrasynovial lacerations without evidence of established synovial infection (27 horses). Group 3 (28 horses) included miscellaneous other conditions. Only minor complications were reported in 12.26% of horses that received IV (n = 155) and 33% of horses that received intraosseous (27) A-RLP. Horses with septic synovitis had a lower survival rate (53.43%) than did horses with lacerations (91.89%). Within group 2, no significant differences in short- or long-term outcomes were found between horses with extrasynovial and fresh, minimally contaminated intrasynovial lacerations. For the horses returning to previous use, 80% of horses with septic synovitis and 72.72% of horses with lacerations were performing at the same or higher level at the time of follow-up.

CONCLUSIONS AND CLINICAL RELEVANCE

The results of the present study indicated that A-RLP is a safe technique with minimal adverse effects. The IV route presented fewer complications than intraosseous injection. Horses with infection of synovial structures had a lower survival rate than did those with acute, minimally contaminated intrasynovial lacerations. The latter had a similar prognosis for horses with extrasynovial lacerations treated with A-RLP.

Higher cefazolin concentrations with intraosseous regional prophylaxis in TKA

BACKGROUND

Prophylactic antibiotics reduce the risk of deep infection after primary TKA. However, conventional systemic dosing may not provide adequate tissue concentrations against more resistant organisms such as coagulase-negative staphylococci. Regional intravenous administration of antibiotics after tourniquet inflation achieves far higher tissue concentrations but requires foot vein cannulation. The intraosseous route may offer a rapid and reliable method of regional administration.

QUESTIONS/PURPOSES

We compared tissue concentrations of cefazolin achieved with systemic versus regional intraosseous administration.

METHODS

Twenty-two patients undergoing primary TKA were randomized into two groups. Group 1 received 1 g cefazolin systemically 10 minutes before tourniquet inflation. Group 2 received 1 g cefazolin intraosseously in 200 mL of normal saline through a tibial cannula after tourniquet inflation and before skin incision. Subcutaneous fat and femoral bone samples were taken at set intervals during the procedure and antibiotic concentrations measured using a validated technique involving high-performance liquid chromatography.

RESULTS

The overall mean tissue concentration of cefazolin in subcutaneous fat was 186 ug/g in the intraosseous group and 11 ug/g in the systemic group. The mean tissue concentration in bone was 130 ug/g in the intraosseous group and 11 ug/g in the systemic group. These differences were consistent across all sample time points throughout the procedure.

CONCLUSIONS

Intraosseous regional administration can achieve concentrations of antibiotic in tissue an order of magnitude higher than systemic administration. Further work is required to determine if this translates into increased efficacy in preventing infection, particularly against coagulase-negative staphylococci.

Indwelling cephalic or saphenous vein catheter use for regional limb perfusion in 44 horses with synovial injury involving the distal aspect of the limb

OBJECTIVE

To describe indwelling cephalic or saphenous vein catheter use for intravenous regional limb perfusion (ID-IV-RLP) to treat horses with synovial injury (contamination/infection) of the distal aspect of the limb.

STUDY DESIGN

Retrospective case series.

ANIMALS

Horses (n = 44; 45 limbs) treated with proximal ID-IV-RLP.

METHODS

Horses had ID-IV-RLP using a cephalic (21 limbs) or saphenous (24 limbs) vein. Amikacin was the most frequently used antibiotic. Number of perfusions ranged from 3 to 21 (median 7). A cast was applied to 14 injured limbs (1 tube cast, 1 full-limb cast, 2 foot casts, and 10 half-limb casts).

RESULTS

Synovial sepsis of the distal portion of 87% of limbs (39) resolved, and 61% of horses returned to soundness. Catheter-related complications occurred in 27% of the limbs but were not significantly associated with outcome. Presence of osteomyelitis was significantly associated with a poor outcome.

CONCLUSIONS

ID-IV-RLP using the cephalic or saphenous vein is an alternative to traditional RLP. An indwelling catheter provided prolonged venous access and facilitated successive perfusions.

Effect of experimentally induced synovitis on amikacin concentrations after intravenous regional limb perfusion

OBJECTIVES

To determine the effects of experimentally induced synovitis of the radiocarpal joint on the intra-articular pharmacokinetics and pharmacodynamics of amikacin after intravenous regional limb perfusion (IVRLP).

STUDY DESIGN

Randomized crossover experimental design.

ANIMALS

Adult horses (n = 8).

METHODS

Horses were randomly assigned into 2 trials: synovitis and no-synovitis. Radiocarpal joint synovitis was induced with lipopolysaccharide 6 hours before IVRLP. IVRLP (5-mg/kg amikacin qs 60 mL) was performed with a pneumatic tourniquet under general anesthesia. Synovial fluid was obtained before and 0.5, 1, 3, 5, 12, 24, 48 hours after IVRLP. Amikacin concentrations at each time point and pharmacokinetic values were compared between synovitis and no-synovitis trials with Student's t-test.

RESULTS

Amikacin synovial fluid concentrations indicated suspected tourniquet failure on 3 occasions (2 synovitis, 1 no-synovitis) on 3 different horses. Data from both trials in these 3 horses were excluded from further analysis. Observed time to maximal concentration (T(max); mean ± SD = 54 ± 13.42 min) was reached earlier in synovitis joints (5/5, 30 min) than in no-synovitis joints (1/5, 30 min and 4/5, 1 h; P = .0476) (P = .0161). Mean observed maximal concentration (C(max)) was higher in synovitis joints (144.48 ± 43.17 μg/mL) than in no-synovitis joints (60.02 ± 28.81 μg/mL; P = .0301). The recommended C(max): minimum inhibitory concentration ratio of 8 was achieved in 3/5 of the successfully perfused joints with induced synovitis, but this ratio was not achieved in any of the clinically normal joints.

CONCLUSION

Synovitis of the radiocarpal joint resulted in an earlier observed T(max) and higher observed C(max) of intra-articular amikacin after IVRLP compared with normal joints.

Efficacy of three tourniquet types for intravenous antimicrobial regional limb perfusion in standing horses

OBJECTIVE

To determine (1) if clinically useful concentrations of amikacin sulfate can be obtained in synovial fluid during regional limb perfusion (RLP) performed above the carpus in standing sedated horses and (2) to determine the efficacy of 3 tourniquet types (narrow rubber [NR], wide rubber [WR], pneumatic [PN]).

ANIMALS

Horses (n=9).

METHODS

Bilateral forelimb RLP with amikacin sulfate (2.5 g) were administered through the cephalic vein in standing sedated horses. Limbs were randomly assigned to the 3 tourniquet types (NR, WR, PN) applied above the carpus. Metacarpophalangeal synovial fluid was obtained 0.5 hour after perfusion. Amikacin concentration in the synovial fluid was detected using fluorescence polarization immunoassay.

RESULTS

Mean synovial concentrations of amikacin in the PN (mean 236 μg/mL; range 23-913 μg/mL) and WR (mean 64.2 μg/mL; range 7-315 μg/mL) were significantly higher (P=.000 and .032, respectively) than the NR tourniquet (mean 2.1 μg/mL; range 0.9-3.3 μg/mL).

CONCLUSIONS

The PN tourniquet resulted in the highest synovial fluid amikacin concentrations in all horses, although administration with PN and WR tourniquets achieved adequate amikacin concentrations. NR tourniquet is ineffective and should not be used for RLP above the carpus in the standing horse.

Antimicrobial delivery by intrasynovial catheterisation with systemic administration for equine synovial trauma and sepsis

OBJECTIVE

To present the technique for intra-articular catheter placement and report the clinical outcomes of 38 cases of equine synovial trauma and/or infection treated with broad-spectrum antimicrobials administered via an intrasynovial catheter (ISC).

DESIGN

Retrospective study.

PROCEDURE

Medical records of 38 horses treated for synovial trauma and sepsis with frequent antimicrobial administration through an ISC from 1995 to 2008 were reviewed. Follow-up information was obtained via clinical re-evaluation or telephone contact with the owners.

RESULTS

The majority of horses (84%) received amikacin and Timentin(R) four times daily. In addition, synovial lavage through the ISC was carried out in 27 horses (71%). Only radiological evidence of osteolysis had a significant negative impact on both lameness at the time of hospital discharge and the long-term outcome. In total, 92% of horses treated with frequent antimicrobial administration through an ISC had clinical resolution of infection. Catheter obstruction occurred in three cases, necessitating replacement or removal, and two synovial fistulae developed at sites of open drainage. The majority of horses treated had a favourable outcome, with 86% being at least pasture sound and 43% returned to riding.

CONCLUSION

Septic synovial structures treated with frequent antimicrobial administration through an ISC had a good prognosis for survival and 43% returned to riding, which is consistent with the results of other studies. The use of a simple ISC should be considered when broad-spectrum intrasynovial antimicrobial administration and lavage of a septic synovial structure are indicated.

New antimicrobials, systemic distribution, and local methods of antimicrobial delivery in horses

The local delivery of antimicrobials is a valuable therapeutic tool with a low morbidity, is practical to use, and is well tolerated by horses. Clinically, its use has allowed equine practitioners to achieve better results when treating musculoskeletal infections, and it represents an extremely useful tool in the practitioner's armamentarium against these types of infections. The technique is indicated to combat orthopedic infections involving bones, joints, physes, tendon sheaths, and foot tissues. Optimal treatment must include other approaches, such as systemic antimicrobial therapy and surgical debridement and lavage, and monitoring of the clinical progression of the patient can help to determine the ideal protocol for each patient.

Evidence-based drug use in equine medicine and surgery

The nature of the equine industry and equine veterinary medicine often requires veterinarians to prescribe drugs with little evidence for a drug's formulation safety or efficacy, or even assurance of the chemistry of the drug used. This means that equine veterinarians must remain skeptics and understand the limitations in their ability to attribute safety and efficacy to a particular drug or treatment. An evidence-based approach to pharmacology demands rigorous testing and an unbiased analysis of results.