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

Pharmacokinetic study of local and systemic gentamicin concentrations after subcutaneous implantation of a gentamicin-impregnated collagen sponge in dogs

This study evaluated the pharmacokinetics of commercial gentamicin-impregnated collagen sponges (GICS) applied subcutaneously in dogs. In six healthy beagles, an 11 ×6 cm subcutaneous pocket was created, a folded 10×10 cm GICS was inserted, and saline was injected to mimic a seroma. Wound fluid samples were aspirated, and the gentamicin concentration was determined. Simultaneously, blood samples were collected to evaluate the corresponding systemic gentamicin concentration. All samples were collected before and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 18, 24, 36, 48, 72, 96, 120, and 168 hours after GICS placement. The local Cmax of gentamicin was reached after 0.5 hours (range, 0.5-1.0 hours) post-implantation in 5/6 dogs at a median concentration of 2053.3 µg/mL (range, 918.0-2791.9 µg/mL). Whitin 24 hours, the local concentration dropped below the MIC for Staphylococcus sp. (4 µg/mL) in 5/6 dogs. Plasma Cmax was achieved at a median of 1.2 hours post-implantation (range, 1.0-2.0 hours) and reached a median concentration of 10.3 µg/mL (range, 8.8-18.03 µg/mL). After 6 hours, the gentamicin concentration in the plasma was below 4 µg/mL in all dogs. The GICS provided a high local concentration of gentamicin in a short time with a local Cmax:MIC ratio of 513:1, largely sufficient to eliminate susceptible bacteria, including methicillin-resistant Staphylococcus pseudintermedius (MRSP) and Pseudomonas sp., in a clinical setting. The repeated administration of saline in the present study seemed to have induced a quicker gentamicin release from the GICS than described in previous studies that typically dealt with "drier" wounds.

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.

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.

The Concentration of Metronidazole in the Distal Interphalangeal Joint following Intravenous Regional Limb Perfusion via the Cephalic Vein in Standing Horses

OBJECTIVE

 The aim of this study was to determine the concentration of metronidazole in the distal interphalangeal joint (DIPJ) of the thoracic limb after administering metronidazole to standing horses by intravenous regional limb perfusion (IVRLP).

METHODS

 Eleven healthy horses had a wide rubber tourniquet applied to the proximal aspect of the antebrachium for 0.5 hours and 500 mg of metronidazole diluted in physiologic saline solution to a total volume of 108 mL was administered by cephalic IVRLP. Synovial fluid samples were collected from the DIPJ before perfusion and at 0.25, 0.5, 2, 12 and 24 hours. Blood samples were obtained at the same time points for serum analysis. Concentrations of metronidazole were determined by liquid chromatography/tandem mass spectrometry.

RESULTS

 Four horses were excluded due to low synovial fluid concentrations and not completing the full tourniquet application time. The C _max in the synovial fluid was 327 ± 208 µg/mL, and the t _max was 26 ± 7 minutes. Only the concentrations of metronidazole at time points 0.25 and 0.5 hours were significantly different (p < 0.001) from synovial concentration before perfusion. The serum C _max was 1.78 ± 0.93 µg/mL, and the t _max was 76 ± 52min.

CONCLUSION

 Metronidazole administered by IVRLP reached high concentrations in the synovial fluid at 0.5 hours. However, the concentrations rapidly decreased below the minimum inhibitory concentration of potential target pathogens. Effectiveness of metronidazole administered by IVRLP as a sole therapy against anaerobic infections of synovial structures of the distal limb cannot be determined by a pharmacokinetic study. However, the present study serves as the basis for future carefully planned clinical trials.

Regenerative Medicine for Equine Musculoskeletal Diseases

Simple Summary

Lameness due to musculoskeletal disease is the most common diagnosis in equine veterinary practice. Many of these orthopaedic disorders are chronic problems, for which no clinically satisfactory treatment exists. Thus, high hopes are pinned on regenerative medicine, which aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. Some regenerative medicine therapies have already made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising but diverse results. This review summarises the current knowledge of commonly used regenerative medicine treatments and critically discusses their use.

Abstract

Musculoskeletal injuries and chronic degenerative diseases commonly affect both athletic and sedentary horses and can entail the end of their athletic careers. The ensuing repair processes frequently do not yield fully functional regeneration of the injured tissues but biomechanically inferior scar or replacement tissue, causing high reinjury rates, degenerative disease progression and chronic morbidity. Regenerative medicine is an emerging, rapidly evolving branch of translational medicine that aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. It includes tissue engineering but also cell-based and cell-free stimulation of endogenous self-repair mechanisms. Some regenerative medicine therapies have made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising results. However, the qualitative and quantitative spatiotemporal requirements for specific bioactive factors to trigger tissue regeneration in the injury response are still unknown, and consequently, therapeutic approaches and treatment results are diverse. To exploit the full potential of this burgeoning field of medicine, further research will be required and is ongoing. This review summarises the current knowledge of commonly used regenerative medicine treatments in equine patients and critically discusses their use.

In vitro Elution of Penicillin, Ampicillin, Tetracycline, Tulathromycin, and Florfenicol From Plaster of Paris Beads

The objectives of this study were to report a recipe for making antibiotic impregnated Plaster of Paris (AI-PoP) beads using penicillin, ampicillin, tetracycline, tulathromycin, and florfenicol and to determine the in vitro elution rates of those antibiotics in the beads. The AI-PoP beads were made using Plaster of Paris powder, antibiotic, and water, cured for 24 h, sterilized by ethylene oxide, and stored up to 5 months before testing. For each antibiotic, 20 beads were combined with bovine serum in sterile tubes and incubated at 37°C on a rocker. Serum was replaced at intervals over the 14 days study period, and antibiotic concentrations were determined by high pressure liquid chromatography with mass spectrometry. Separately, in a proof-of-concept study, the growth of E. coli and T. pyogenes in eluent from 10 beads for each antibiotic was quantified by flow cytometry. Antibiotic was detected in AI-PoP bead eluent for 14 days for all but the ampicillin beads, for which antibiotic was detected for 8 days. The concentration of antibiotic in eluent was greater than the minimum inhibitory concentration (MIC) of tested bacteria for the entire study period for penicillin, tetracycline, tulathromycin, and florfenicol. The concentration of ampicillin remained greater than the MIC of E. coli for 4 days and T. pyogenes for 6 days. The colony forming units (CFU)/ml of live E. coli and T. pyogenes was reduced over a 72-h period by 1-3 log10 CFU, with the exception of tetracycline, which reduced CFU/ml of T. pyogenes by Collapse

Key Words

• Plaster of Paris
• antibiotics
• cattle
• elution
• wound infection

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Affiliation(s)

Paul Merkatoris Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
Jennifer Schleining Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, United States
Adam Krull Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
David Borts Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
Virginia Fajt Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, United States

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Surgical intervention for vertebral osteomyelitis in a calf

OBJECTIVE

To report the surgical treatment and outcome of a non-ambulatory calf with cervical vertebral ostoeomyelitis.

STUDY DESIGN

Clinical report.

SAMPLE POPULATION

One 3.5-month-old female mixed-breed calf with tetraparesis of 3 months duration.

METHODS

After computed tomography-guided bone biopsy, a bacterial osteolytic lesion within the body of the fourth cervical vertebrae (C4) and resultant pathologic compression fracture clinically resulting in full tetraparesis was diagnosed in the calf. Culture results from the lesion within C4 confirmed a diagnosis of Trueperella pyogenes.

RESULTS

Poor response to medical management justified surgical debridment of the lesion in C4 and subsequent stabilization of the cervical vertebral column. A three-part procedure was performed including (1) debridement of the C4, (2) bilateral ventral vertebral stabilization from C3 to C5, and (3) placement of ampicillin-impregnated plaster of Paris beads within the body of C4. With postoperative physical rehabilitation, the calf regained full ambulatory function. At 1-month follow-up, the calf remained ambulatory with mild proprioceptive ataxia and no evidence of implant failure. At annual recheck, the calf had gained 208 kg and remained fully ambulatory with no residual neurologic deficits.

CONCLUSION

Surgical intervention and use of antibiotic-impregnated implants offered a viable alternative to long-term medical management of vertebral osteomyelitis in the calf reported here.

CLINICAL SIGNIFICANCE

This case identifies surgical intervention as a potential means for improving outcomes in a historically fatal condition of production animals.

Magnetic resonance imaging following regional limb perfusion of gadolinium contrast medium in 26 horses

BACKGROUND

Systemic administration of gadolinium contrast medium is common in small animals to increase lesion conspicuity and determine vascularisation of lesions identified with magnetic resonance imaging (MRI); however, the large volume required for systemic administration limits its use in horses.

OBJECTIVES

The purpose of this study was to assess the feasibility of administering a low dose of contrast medium via venous regional limb perfusion.

STUDY DESIGN

Prospective clinical study.

METHODS

Distal limbs of 26 horses (one limb per horse) were imaged with MRI before and after administration of 5 mL of gadopentetate dimeglumine (Magnevist^® ) diluted with 5 mL of physiological saline via a palmar/plantar digital vein with a tourniquet in place at the level of the mid aspect of the third metacarpal/metatarsal bone. Commonly assessed structures of the equine distal limb were examined for normal and abnormal contrast enhancement.

RESULTS

Twenty-five of 26 horses had adequate contrast enhancement of their distal limb. The lack of adequate contrast enhancement in one limb was likely associated with failure of the tourniquet. No adverse reactions were identified in any horse. One hundred thirty-two lesions were detected, of which, 69 contrast enhanced. Twelve lesions were detected exclusively following contrast enhancement.

MAIN LIMITATIONS

Case numbers and lesion variability yielded insufficient data to perform statistical analyses. Histopathology was not performed on sound horses to determine if the imaged structures were normal.

CONCLUSIONS

Regional limb perfusion is a feasible method to administer gadolinium contrast material to the equine distal limb for MRI. The enhancement pattern of the equine distal limb in sound horses is described. Contrast enhanced MRI of the distal equine limb helps to further characterise lesions identified with precontrast images, including adhesions and deep digital flexor tendinopathy. Contrast enhanced MRI also aids in identification of additional lesions, such as neovascularisation.

Pharmacokinetics of ceftazidime after regional limb perfusion in standing horses

OBJECTIVE

To determine the metacarpophalangeal joint fluid concentrations of ceftazidime administered via regional limb perfusion (RLP).

ANIMALS

Eight healthy horses.

METHODS

RLP was performed by injecting 2 g of ceftazidime and 60 mL of perfusate volume in the cephalic vein of standing, sedated horses. Serum and synovial fluid from the metacarpophalangeal joint were collected before perfusion and at 0.5, 2, 6, 12, 24 hours postperfusion. Ceftazidime concentrations were measured via liquid chromatography. Maximal concentration (C_max ), area under the curve (AUC), half-life of the drug (T ½), and the timing of C_max (T_max ) were determined to assess ceftazidime as a candidate drug for RLP. Continuous parameters were compared with the Mann-Whitney U test. P value ≤ .05 was considered statistically significant.

RESULTS

The C_max of ceftazidime in synovial fluid (235 µg/mL) was 15 times higher than the minimal inhibitory concentration (MIC) for most bacteria involved in orthopedic infections, including resistant pathogens such as Pseudomonas aeruginosa (MIC = 16 µg/mL). However, synovial concentrations decreased quickly and remained above the MIC in only 1 horse by 6 hours postperfusion.

CONCLUSION

RLP generated high synovial fluid concentrations of ceftazidime in the distal limb, but these concentrations decreased rapidly below the deliberately high MIC selected.

CLINICAL RELEVANCE

Once daily RLP, as applied in our study, with 2 g ceftazidime in standing horses, cannot be recommended for use in a clinical setting.

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.

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.

Mastocytoma in the common carpal sheath of the digital flexor tendons of a horse

A 13-year-old Morgan gelding was examined for right forelimb lameness and tenosynovitis of the right common carpal sheath of the digital flexor tendons. The horse had moderate right forelimb lameness at the trot and marked effusion of the right common carpal sheath of the digital flexor tendons. Ultrasonographic examination revealed a soft tissue mass within the proximal pouch of the affected tendon sheath, located adjacent to the distal physis of the radius. Cytology and culture of the fluid revealed a sterile, eosinophilic tenosynovitis. Tenoscopic exploration confirmed the presence of a capsulated soft tissue mass. Thecotomy was required to fully debride the mass, which histology revealed to be a mast cell tumour. At 22 months postoperatively, the horse developed mild right forelimb lameness and eosinophilic tenosynovitis because of recurrence of the mastocytoma. Mastocytosis is a possible differential diagnosis in any horse exhibiting lameness associated with tenosynovitis. Surgical excision combined with rest and postoperative intrasynovial and systemic corticosteroids may be palliative.