Pharmacokinetics of tobramycin following intravenous, intramuscular, and intra-articular administration in healthy horses

Intra-articular administration of antibiotics in horses: Justifications, risks, reconsideration of use and outcomes

Antibiotics have been injected intra-articularly by equine veterinarians for decades, either prophylactically when other drugs are administered for osteoarthritis or therapeutically to treat septic arthritis. This route of administration has also more recently gained attention in human orthopaedic clinical practice, particularly as an alternative to systemic antibiotic administration to treat infections following prosthetic arthroplasty. While the rationale for injecting antibiotics intra-articularly has been largely focused on achieving high local drug concentrations, there has been relatively little focus on pharmacokinetic parameters of antibiotics administered by this route, or on the potential for local toxicity. The increasing incidence of antibiotic resistance in veterinary and human medicine prompts reconsideration of off-label antibiotic usage and evaluation of evidence-based dosing strategies. The purpose of this review was to summarise the current literature describing intra-articular antibiotic usage, including specific studies where pharmacokinetics, potential safety and toxicity have been evaluated. This review will advance practitioners' understanding of the use of intra-articularly administered antibiotics, including the overall pros and cons of the approach.

Antimicrobial resistance spectrum conferred by pRErm46 of emerging macrolide (multidrug)-resistant Rhodococcus equi

Clonal multidrug resistance recently emerged in Rhodococcus equi, complicating the therapeutic management of this difficult-to-treat animal and human pathogenic actinomycete. The currently spreading multidrug-resistant (MDR) "2287" clone arose in equine farms upon acquisition, and co-selection by mass macrolide-rifampin therapy, of the pRErm46 plasmid carrying the erm(46) macrolides-lincosamides-streptogramins resistance determinant, and an rpoB^S531F mutation. Here, we screened a collection of susceptible and macrolide-rifampin-resistant R. equi from equine clinical cases using a panel of 15 antimicrobials against rapidly growing mycobacteria (RGM), nocardiae and other aerobic actinomycetes (NAA). R. equi -including MDR isolates- was generally susceptible to linezolid, minocycline, tigecycline, amikacin and tobramycin according to Staphylococcus aureus interpretive criteria, plus imipenem, cefoxitin and ceftriaxone based on Clinical & Laboratory Standards Institute (CLSI) guidelines for RGM/NAA. Ciprofloxacin and moxifloxacin were in the borderline category according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Molecular analyses linked pRErm46 to significantly increased MICs for trimethoprim-sulfamethoxazole and doxycycline in addition to clarithromycin within the RGM/NAA panel, and to streptomycin, spectinomycin and tetracycline resistance. pRErm46 variants with spontaneous deletions in the class 1 integron (C1I) region, observed in ≈30% of erm(46)-positive isolates, indicated that the newly identified resistances were attributable to C1I's sulfonamide (sul1) and aminoglycoside (aaA9) resistance cassettes and adjacent tetRA(33) determinant. Most MDR isolates carried the rpoB^S531F mutation of the 2287 clone, while different rpoB mutations (S531L, S531Y) detected in two cases suggest the emergence of novel MDR R. equi strains.

Evaluation of Intra-Articular Amikacin Administration in an Equine Non-inflammatory Joint Model to Identify Effective Bactericidal Concentrations While Minimizing Cytotoxicity

Septic arthritis causes significant morbidity and mortality in veterinary and human clinical practice and is increasingly complicated by multidrug-resistant infections. Intra-articular (IA) antibiotic administration achieves high local drug concentrations but is considered off-label usage, and appropriate doses have not been defined. Using an equine joint model, we investigated the effects of amikacin injected at three different doses (500, 125, and 31.25 mg) on the immune and cartilage responses in tibiotarsal joints. Synovial fluid (SF) was sampled at multiple time points over 24 h, the cell counts determined, and amikacin concentrations measured by liquid chromatography-mass spectrometry. Cytokine concentrations and collagen degradation products in SF were measured by ELISA and multiplex immunoassays. The mean amikacin concentrations in SF were greater than or equal to the minimum inhibitory concentration (MIC) (0.004 mg/ml) for most common equine joint pathogens at all time points tested to 24 h for all three amikacin doses evaluated. The inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) increased significantly in SF in the highest amikacin dose group, despite the fact that increases in SF cell counts were not observed. Similarly, the biomarkers of cartilage type II collagen cleavage (C2C and C12C) were increased in SF following amikacin injection. Mechanistically, we further demonstrated using in vitro studies that chondrocytes and synoviocytes killed by exposure to amikacin underwent apoptotic cell death and were phagocytosed by macrophages in a non-inflammatory process resembling efferocytosis. Neutrophils and T cells were susceptible to amikacin cytotoxicity at clinically relevant doses, which may result in blunting of cellular inflammatory responses in SF and account for the lack of increase in total nucleated cell counts following amikacin injection. In summary, decisions on whether to inject cytotoxic antibiotics such as aminoglycosides intra-articularly and what doses to use should take into account the potential harm that antibiotics may cause and consider lower doses than those previously reported in equine practice.

Use of in vitro assays to identify antibiotics that are cytotoxic to normal equine chondrocytes and synovial cells

BACKGROUND

Intra-articular (IA) antibiotic usage is prevalent in equine practice. However, recent emergence of antimicrobial resistance prompts re-evaluation of antibiotic selection, particularly when used prophylactically. Furthermore, many commonly used antibiotics exert direct cytotoxicity to equine cells, and appropriate IA doses have not been defined.

OBJECTIVES

To screen antibiotics in vitro as an initial assessment of cytotoxicity against normal equine joint cells in monolayer culture and explant tissues.

STUDY DESIGN

In vitro experimental study.

METHODS

Chondrocytes and synovial cells were harvested from three horses and plated on 24-well plates (100 000 cells/wells in triplicate) for 48 hours prior to addition of antibiotics. Joint cells were exposed to antibiotics (n = 15) at various doses (25-0.39 mg/mL in complete DMEM media) for 24 hours and viability was assessed by trypan blue dye exclusion. The half maximal inhibitory concentration (IC50) was determined for each antibiotic. Cartilage explants were obtained from 3 horses, minced and exposed to antibiotics (n = 5) for 72 hours. Live/dead staining was performed, and fluorescence was visualised using Olympus IX83 spinning disk confocal microscope. Percentage of live vs dead cells was quantified.

RESULTS

Antibiotics from different antimicrobial classes expressed dose-dependent but variable cytotoxicity to equine joint cells in vitro. Aminoglycosides and doxycycline had the lowest IC50 (most toxic). Ampicillin sulbactam, imipenem, tobramycin, ceftiofur sodium and amoxicillin had IC50 > 25 mg/mL for at least one cell line, representing potentially less cytotoxic alternatives.

MAIN LIMITATIONS

Further studies are necessary to extrapolate these in vitro data results to the in vivo joint environment.

CONCLUSIONS

Targeted IA antibiotic therapy would involve selection of the safest antibiotics (highest IC50) with efficacy based on bacterial culture/sensitivity. Antimicrobial selection and evidence-based dosing may minimise damage to native articular cartilage and synovial cells and development of antimicrobial resistance when IA antibiotics are used in equine practice.

Evaluation of an osteochondral fragment-groove procedure for induction of metacarpophalangeal joint osteoarthritis in horses

OBJECTIVE To evaluate lameness and morphological changes associated with an osteochondral fragment-groove procedure as a means of experimental induction of metacarpophalangeal (MCP) joint osteoarthritis within an 11-week period in horses. ANIMALS 6 nonlame adult warmbloods. PROCEDURES The right MCP joint of each horse underwent an osteochondral fragment-groove procedure (day 0). After 1 week of stall rest (ie, starting day 7), each horse was trained daily on a treadmill. Weekly, horses underwent visual and inertial sensor-based assessments of lameness. Both MCP joints were assessed radiographically on days 0 (before surgery), 1, 35, and 77. A synovial fluid sample was collected from the right MCP joint on days 0 (before surgery), 35, 36, 49, 63, and 77 for cytologic and biomarker analyses. On day 77, each horse was euthanized; both MCP joints were evaluated macroscopically and histologically. RESULTS Right forelimb lameness was detected visually and by the inertial sensor system when horses were moving on a straight line after distal forelimb flexion or circling left on days 14 to 77. Compared with presurgical values, synovial fluid interleukin-6, prostaglandin E2, hyaluronic acid, and interleukin-1 receptor antagonist protein concentrations were increased at 2 or 3 time points, whereas tumor necrosis factor-α and interleukin-10 concentrations were decreased at 1 time point. Gross examination of all right MCP joints revealed synovitis and wear lines; synovitis was confirmed histologically. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a combined osteochondral fragment-groove procedure can be used to induce clinically and grossly observable early MCP joint osteoarthritis during an 11-week period in horses.

Optimization of Antimicrobial Treatment to Minimize Resistance Selection

Optimization of antimicrobial treatment is a cornerstone in the fight against antimicrobial resistance. Various national and international authorities and professional veterinary and farming associations have released generic guidelines on prudent antimicrobial use in animals. However, these generic guidelines need to be translated into a set of animal species- and disease-specific practice recommendations. This article focuses on prevention of antimicrobial resistance and its complex relationship with treatment efficacy, highlighting key situations where the current antimicrobial drug products, treatment recommendations, and practices may be insufficient to minimize antimicrobial selection. The authors address this topic using a multidisciplinary approach involving microbiology, pharmacology, clinical medicine, and animal husbandry. In the first part of the article, we define four key targets for implementing the concept of optimal antimicrobial treatment in veterinary practice: (i) reduction of overall antimicrobial consumption, (ii) improved use of diagnostic testing, (iii) prudent use of second-line, critically important antimicrobials, and (iv) optimization of dosage regimens. In the second part, we provided practice recommendations for achieving these four targets, with reference to specific conditions that account for most antimicrobial use in pigs (intestinal and respiratory disease), cattle (respiratory disease and mastitis), dogs and cats (skin, intestinal, genitourinary, and respiratory disease), and horses (upper respiratory disease, neonatal foal care, and surgical infections). Lastly, we present perspectives on the education and research needs for improving antimicrobial use in the future.

Single intra-articular injection of fluvastatin-PLGA microspheres reduces cartilage degradation in rabbits with experimental osteoarthritis

Statins are cholesterol-lowering drugs that inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme of the mevalonate pathway. The anti-inflammatory effect of statins has been reported in recent years. The present study investigated therapeutic effects of the local administration of statin in osteoarthritis (OA). We assessed clinically used statins and selected fluvastatin for further experimentation, as it showed potent anabolic and anti-catabolic effects on human OA chondrocytes. To achieve controlled intra-articular administration of statin, we developed an intra-articular injectable statin using poly(lactic-co-glycolic acid) (PLGA) as a drug delivery system (DDS). The release profile of the statin was evaluated in vitro. Finally, therapeutic effects of fluvastatin-loaded PLGA microspheres (FLU-PLGA) were tested in a rabbit OA model. Rabbit knees were divided into four subgroups: group 1-A, PLGA-treated group; group 1-B, PLGA contralateral saline control group; group 2-A, FLU-PLGA-treated group; and group 2-B, FLU-PLGA contralateral saline control group. Histological analysis 5 weeks after intra-articular injection revealed that OARSI scores were lower in group 2-A. No significant differences in OARSI scores were observed between groups 1-A, 1-B, and 2-B. This study indicates that a single intra-articular injection of fluvastatin-loaded PLGA microspheres could be a novel therapeutic approach for treating patients with OA. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2465-2475, 2017.