Septic arthritis in foals

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.

Antimicrobial Selection for the Equine Practitioner

Antimicrobial drugs play an important, often central, role in the therapeutic management of mature horses and foals with a variety of illnesses, including those requiring critical care. Antimicrobial use must be based on rational principles involving thorough patient evaluation and sound clinical judgment that indicate a high likelihood that the patient has a bacterial infection and that antimicrobials are indicated to promote recovery. The aim of antimicrobial treatment is to inflict an insult on infecting bacteria sufficient to kill the organism or render it susceptible to inactivation by natural host defenses or the local microenvironment without adversely affecting the patient.

Factors associated with survival and racing performance of 114 Thoroughbred foals with septic arthritis compared with maternal siblings (2009-2015)

BACKGROUND

There is little consensus on factors associated with survival in foals with septic arthritis and limited data on long-term racing performance of Thoroughbred foals treated for septic arthritis. A more thorough understanding of short- and long-term outcome is necessary to help inform owners, and subsequently guide treatment.

OBJECTIVES

To investigate factors associated with survival, and to analyse racing performance of foals with septic arthritis compared with their maternal siblings.

STUDY DESIGN

Retrospective cohort and a case-control study.

METHODS

Veterinary clinical records of Thoroughbred foals ≤180 days old that underwent arthroscopic, cannulae or through-and-through needle lavage for the treatment of septic arthritis between 2009 and 2015 were reviewed. Data included signalment, and clinicopathological information. The dam's foaling records were reviewed and the lifetime racing records were obtained for affected foals and two of their maternal siblings. Logistic regression analysis was used to determine factors associated with survival to discharge or racing. Comparisons between treated foals and their maternal siblings were made.

RESULTS

Ninety (78%) of 115 foals diagnosed with septic arthritis were discharged alive. Foals <26 days old at the time of admission were five times less likely (P = .003) and foals with concurrent multisystemic disease were six times less likely (P = .02) to be discharged alive. Sixty (67%) foals discharged alive started in ≥1 race, and there was no difference in the proportion of foals that started in a race or racing performance between foals treated for septic arthritis and their maternal siblings.

MAIN LIMITATIONS

Retrospective study design, limited number of foals with multiple joint involvement and failure to accurately record duration of clinical signs.

CONCLUSIONS

Foals treated for septic arthritis at the Scone Equine Hospital, New South Wales, Australia had a good prognosis for survival, and for this cohort, foals that survived to discharge had a similar ability to race as their maternal siblings.

Comparison of conventional radiography and computed tomography as aids in the diagnosis of osteomyelitis in 11 foals

BACKGROUND

Conventional radiography is currently the most common imaging modality used by veterinarians investigating foals with suspected osteomyelitis. Emerging evidence in adult horses and humans suggests computed tomography (CT) is a superior modality for evaluation of osseous changes in general. This study aimed to evaluate the potential benefits of CT versus conventional radiography in cases of osteomyelitis in foals.

METHODS

Cases of osteomyelitis in foals under 6 months of age admitted over a 6-year period at a single referral hospital that had both CT and conventional radiography images were retrieved. Case details and measurements of the largest area of bone lysis identified in two planes (lateromedial/sagittal and dorsopalmar/dorsal) were evaluated by three veterinarians with a range of experience.

RESULTS

A significant difference regarding lesion size was seen on the lateromedial (LM) radiographic projections compared with the equivalent sagittal plane CT image. The LM radiographic evaluation resulted in a 37% underestimation of the area of the lesion. Additionally, use of the LM radiographic projections were 2.5-fold more variable in the measurement area compared with CT. In general, regardless of projection, CT produced more information regarding lesion area and, in some cases, detected osseous changes that were not evident on the radiographs.

CLINICAL RELEVANCE

LM radiographic projections are less reliable and commonly result in an under-appreciation of lesion size and extent. CT detected lesions that were difficult or impossible to identify on radiographs and may allow improved treatment planning.

Treatment of septic arthritis of the coxofemoral joint in 12 foals

OBJECTIVE

To describe the clinical signs, surgical treatment, and outcome of septic arthritis of the coxofemoral joint in foals.

STUDY DESIGN

Retrospective clinical study.

SAMPLE POPULATION

Foals (n = 12) with confirmed sepsis of the coxofemoral joint.

METHODS

Lameness was localized to the coxofemoral joint based on physical examination. Sepsis was confirmed by cytological analysis of synovial fluid obtained under ultrasonographic guidance, during general anesthesia or standing sedation. Intra-articular analgesia was used as an adjunct diagnostic modality in 2 foals. Surgical lavage of the affected joint was performed via arthroscopy or needle lavage, with repeated lavage performed in 7 foals.

RESULTS

Synovial fluid contained 4.4 to 173 × 10⁹ /L white blood cells (WBCs), and 38-63 g/L total protein. Cultures were positive in 10/12 foals. Isolated organisms included Salmonella spp., Streptococcus spp., Rhodococcus spp., Enterococcus spp., Escherichia spp., Staphylococcus spp., Acinetobacter spp., Methicillin-resistant Staphylococcus aureus and Bacillus spp. Ten foals were discharged from hospital (83%). One of these was euthanized 15 days later due to chronic intestinal salmonellosis and renal failure, and 9 foals survived with no residual lameness detected 1 year after discharge from hospital.

CONCLUSIONS

Sepsis of the coxofermoral joint can be effectively treated with a combination of arthroscopic lavage and the use of systemic and local antimicrobials.

Ultrasonographic findings in 38 horses with septic arthritis/tenosynovitis

Septic arthritis/tenosynovitis in the horse can have life-threatening consequences. The purpose of this cross-sectional retrospective study was to describe ultrasound characteristics of septic arthritis/tenosynovitis in a group of horses. Diagnosis of septic arthritis/tenosynovitis was based on historical and clinical findings as well as the results of the synovial fluid analysis and/or positive synovial culture. Ultrasonographic findings recorded were degree of joint/sheath effusion, degree of synovial membrane thickening, echogenicity of the synovial fluid, and presence of hyperechogenic spots and fibrinous loculations. Ultrasonographic findings were tested for dependence on the cause of sepsis, time between admission and beginning of clinical signs, and the white blood cell counts in the synovial fluid. Thirty-eight horses with confirmed septic arthritis/tenosynovitis of 43 joints/sheaths were included. Degree of effusion was marked in 81.4% of cases, mild in 16.3%, and absent in 2.3%. Synovial thickening was mild in 30.9% of cases and moderate/severe in 69.1%. Synovial fluid was anechogenic in 45.2% of cases and echogenic in 54.8%. Hyperechogenic spots were identified in 32.5% of structures and fibrinous loculations in 64.3%. Relationships between the degree of synovial effusion, degree of the synovial thickening, presence of fibrinous loculations, and the time between admission and beginning of clinical signs were identified, as well as between the presence of fibrinous loculations and the cause of sepsis (P ≤ 0.05). Findings indicated that ultrasonographic findings of septic arthritis/tenosynovitis may vary in horses, and may be influenced by time between admission and beginning of clinical signs.