Effect of induced synovial inflammation on pharmacokinetics and synovial concentration of sodium ampicillin and kanamycin sulfate after systemic administration in ponies

Longitudinal evaluation of fentanyl concentrations in equine plasma and synovial fluid following application of transdermal fentanyl patches over one carpal joint

OBJECTIVE

To determine if transdermally delivered fentanyl can achieve greater concentrations of fentanyl in synovial fluid when applied over a synovial structure.

STUDY DESIGN

Randomized, experimental study.

ANIMALS

Six healthy adult horses.

METHODS

Each horse had two 100 μg/h fentanyl matrix patches applied on the dorsal aspect of one, randomly assigned, carpometacarpal joint (CMCJ) for 48 h. Whole blood and bilateral synovial samples from the intercarpal joint were obtained at 0, 2, 6, 12, 24, 36 and 48 h. Fentanyl concentrations were measured with liquid chromatography-mass spectrometry.

RESULTS

All subjects achieved detectable concentrations of fentanyl in both plasma and synovial fluid. Time to peak synovial and plasma concentration was 12 h. At 6 h, the synovial concentration in the untreated carpus (0.104 ng/mL ± 0.106) was lower than plasma fentanyl concentrations 0.31 ± 0.27 (p = .036). At 12 h, both treated (0.55 ng/mL ± 0.3) and untreated (0.53 ng/mL ± 0.28) synovial fluid fentanyl concentrations were lower than plasma (0.87 ng/mL ± 0.48) concentrations (p < .001 and p = .001, respectively). Synovial concentrations of fentanyl did not differ between treated and untreated joints (p > 0.608 for all time points).

CONCLUSION

Application of fentanyl matrix patches directly over the CMCJ did not result in increased fentanyl concentrations in the synovial fluid of the treated intercarpal joint in normal horses.

CLINICAL SIGNIFICANCE

There is likely no analgesic advantage to placing fentanyl patches directly over the affected joint, as it did not result in increased synovial concentrations at the tested site.

Susceptibility of canine chondrocytes and synoviocytes to antibiotic cytotoxicity in vitro

OBJECTIVE

To evaluate relative cytotoxicity of antibiotics to normal canine joint tissues in vitro.

STUDY DESIGN

Experimental in vitro study.

SAMPLE POPULATION

Chondrocytes and synoviocytes (three dogs); cartilage explants (three dogs); six dogs total.

METHODS

Chondrocytes and synoviocytes from normal femoropatellar joints of three dogs were plated on 24-well plates (50 000 cells/cm² , triplicate, 48 hours) and exposed to antibiotics (ampicillin sulbactam, vancomycin, cefazolin, ceftazidime, amikacin, enrofloxacin; 0.39-25 mg/mL, 24 hours). Viability was assessed by using trypan blue dye exclusion. Antibiotic concentrations at which 50% cell death occurred (half-maximal inhibitory concentration) were determined to rank antibiotics for relative cytotoxicity. Occurrence of caspase-3 expression after antibiotic exposure was assessed as an indication of apoptosis induction. Cartilage explants from three different dogs were minced and exposed to antibiotics (amikacin, ceftazidime, cefazolin, enrofloxacin; 5 mg/mL, 72 hours). Live/dead staining was performed, and fluorescence was visualized by using confocal microscopy. Percentage of live vs dead cells was quantitated.

RESULTS

Viability of chondrocytes and synoviocytes decreased with increasing antibiotic concentrations. Half-maximal inhibitory concentrations were determined for synoviocytes (vancomycin 13.77, ampicillin sulbactam 3.07, amikacin 2.26, ceftazidime 1.62, cefazolin 1.48, enrofloxacin 1.25 mg/mL) and chondrocytes (vancomycin 8.65, ampicillin sulbactam 8.63, ceftazidime 3.16, amikacin 2.74, cefazolin 1.67, enrofloxacin 0.78 mg/mL). Caspase-3 expression was upregulated, providing evidence that apoptotic pathways were active in cell death.

CONCLUSION

Half-maximal inhibitory concentration data provided evidence of lower toxicity of vancomycin and ampicillin sulbactam to joint tissues in vitro.

CLINICAL SIGNIFICANCE

These results provide evidence to justify future in vitro work with osteoarthritic joint tissues and in vivo clinical trials to evaluate safety and efficacy of intra-articular antibiotics to treat dogs with septic arthritis.

Dose-Finding in the Development of an LPS-Induced Model of Synovitis in Sheep

Models of transient synovitis that can be controlled with antiinflammatory and analgesic drugs have been used to study pain amelioration. To this end, we aimed to determine the dose of intraarticularly administered E. coli LPS that induced signs of synovitis without systemic signs in clinically healthy male castrated sheep (n = 14). In phase 1, a single dose of LPS (0.5, 1.0, 1.5, or 2.0 ng in a total volume of 0.5 mL) was administered into the right stifle joint. In phase 2, a dose of LPS (1.0 or 2.0 μg) in 0.3 mL was administered to 4 naïve sheep. In phase 3, 4 sheep from phase 1 were inoculated after a 60 d washout period with either 0.5 or 1.0 μg of LPS. During the first 48 h after LPS administration, the following were performed: assessment of clinical parameters; scoring for lameness, pain on limb flexion, and local swelling; and ultrasonography of the joints were performed. The doses tested during phase 1 produced subtle signs. During phase 2, mild to moderate lameness with no evidence of systemic signs occurred at both doses. In phase 3, clinical responses were similar between the 0.5- and 1-μg doses. Signs of swelling were not observed at any time. Therefore, we consider the 0.5-μg to be the most appropriate for this model, because it was the lowest dose tested capable of causing lameness without signs of systemic inflammation in all animals.

Identification of Body Behaviors and Facial Expressions Associated with Induced Orthopedic Pain in Four Equine Pain Scales

Simple Summary

Pain scales are tools developed to improve pain assessment in horses. They are based on behaviors and/or facial expressions, and the observer allocates a score based on the character of the behavior or facial expression. Little is known about behaviors and facial expressions at rest in horses with orthopedic pain since pain is mainly assessed by lameness evaluation during movement. The aim of this study was to describe how closely equine behaviors and facial expressions are associated with movement asymmetry and to identify combinations of behavior and expressions present in horses with induced orthopedic pain. Orthopedic pain was induced in eight horses and assessed in two ways; using four existing equine pain scales at rest, and by measuring movement asymmetry during movement. The association of behavior and facial expression items in the pain scales with actual lameness was analyzed. Posture-related behavior showed the strongest association, while facial expressions varied between horses. These results show that pain scales for orthopedic pain assessment would benefit from including posture, head position, location in the box stall, focus, interactive behavior, and facial expressions. This could improve orthopedic pain detection in horses during rest with mild lameness.

Abstract

Equine orthopedic pain scales are targeted towards horses with moderate to severe orthopedic pain. Improved assessment of pain behavior and pain-related facial expressions at rest may refine orthopedic pain detection for mild lameness grades. Therefore, this study explored pain-related behaviors and facial expressions and sought to identify frequently occurring combinations. Orthopedic pain was induced by intra-articular LPS in eight horses, and objective movement asymmetry analyses were performed before and after induction together with pain assessments at rest. Three observers independently assessed horses in their box stalls, using four equine pain scales simultaneously. Increase in movement asymmetry after induction was used as a proxy for pain. Behaviors and facial expressions commonly co-occurred and were strongly associated with movement asymmetry. Posture-related scale items were the strongest predictors of movement asymmetry. Display of facial expressions at rest varied between horses but, when present, were strongly associated with movement asymmetry. Reliability of facial expression items was lower than reliability of behavioral items. These findings suggest that five body behaviors (posture, head position, location in the box stall, focus, and interactive behavior) should be included in a scale for live assessment of mild orthopedic pain. We also recommend inclusion of facial expressions in pain assessment.

Antimicrobial susceptibility patterns of bacterial isolates cultured from synovial fluid samples from horses with suspected septic synovitis: 108 cases (2008-2017)

OBJECTIVE

To describe the antimicrobial susceptibility patterns of the most commonly isolated bacteria cultured from synovial fluid samples from horses with suspected septic synovitis treated at an equine referral hospital between May 1, 2008, and September 24, 2017.

SAMPLE

131 synovial fluid samples from 108 client-owned horses.

PROCEDURES

A retrospective medical record search was conducted to identify horses with suspected septic synovitis and results of synovial fluid bacterial culture and antimicrobial susceptibility testing. Data collected included signalment, known or suspected origin of synovial contamination, synovial structures affected, antimicrobial treatment, and results of synovial fluid cytologic evaluation and bacterial culture and susceptibility testing. Horses were grouped as adults (≥ 6 months old) or foals (< 6 months old).

RESULTS

Results of bacterial culture were positive for 34 of 70 (49%) and 18 of 61 (30%) samples from 68 adult horses and 40 foals, respectively. Gram-positive bacteria were more common in adult horses, whereas gram-negative bacteria were more common in foals. No multidrug-resistant microorganisms were identified. For adult horses, 92% (23/25) of gram-positive isolates tested with penicillin and gentamicin were susceptible to the combination. For foals, 94% (15/16) of isolates tested with penicillin, gentamicin, or both had susceptibility to 1 or both antimicrobials.

CONCLUSIONS AND CLINICAL RELEVANCE

Periodic review of bacterial profiles and antimicrobial susceptibility in horses with septic synovitis can help to detect early changes in bacterial pressure and antimicrobial resistance. Findings suggested that in the geographic area we serve, a combination of penicillin and gentamicin would be an effective empirical antimicrobial treatment for most horses with septic synovitis while results of bacterial culture and susceptibility are pending.

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.

Amikacin induces rapid dose-dependent apoptotic cell death in equine chondrocytes and synovial cells in vitro

BACKGROUND

Equine veterinarians frequently inject aminoglycoside antibiotics intra-articularly, either to treat septic arthritis or for prophylaxis with other medications when injecting joints for osteoarthritis. Although aminoglycosides have been demonstrated to be toxic to equine mesenchymal stem cells (MSC), their effects on resident joint cells have not been previously investigated. Moreover, safe and effective intra-articular doses have not been defined.

OBJECTIVES

To determine effects of concentration, duration of exposure, pH and the presence of synovial fluid on the cytotoxic effects of amikacin on equine chondrocytes, synoviocytes and bone marrow- and adipose-derived MSC.

STUDY DESIGN

In vitro experimental study.

METHODS

Four cell types were harvested from three donor horses and plated in triplicate wells for 48 hours prior to the addition of amikacin. The effects of amikacin on cell viability were assessed for different exposure times, concentrations and with pH buffered or unbuffered in media, as well as in the presence of synovial fluid. Cell metabolism/viability was assessed by colorimetric MTT assay. Cell proliferation was assessed by live cell imaging. Cell viability was assessed using trypan blue and dimeric cyanine nucleic acid stain (yoyo-1). To determine the mechanism of cell death, apoptosis was evaluated using Annexin V and 7AAD staining with flow cytometric quantification. Induction of apoptotic cell death pathways was assessed using caspase-3 expression.

RESULTS

Amikacin is cytotoxic to equine joint cells and MSC in a rapid, dose-dependent, pH-independent manner, which occurs primarily by apoptosis. Amikacin cytotoxicity was not mitigated by the addition of synovial fluid in vitro.

MAIN LIMITATIONS

Further studies are necessary to determine whether these in vitro results predict joint injury in live animal models.

CONCLUSIONS

Amikacin at clinically applied doses induces rapid, pronounced cell death of equine joint cells. These findings suggest that amikacin doses currently used intra-articularly should be reconsidered pending in vivo joint titration studies.

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.

Joint inflammation increases glucosamine levels attained in synovial fluid following oral administration of glucosamine hydrochloride

OBJECTIVE

To compare synovial glucosamine levels in normal and inflamed equine joints following oral glucosamine administration and to determine whether single dose administration alters standard synovial parameters of inflammation.

METHODS

Eight adult horses were studied. On weeks 1 and 2, all horses received 20mg/kg glucosamine hydrochloride by nasogastric (NG) intubation or intravenous injection. On weeks 3 and 4, 12h after injection of both radiocarpal joints with 0.25 ng Escherichia coli lipopolysaccharide (LPS) to induce inflammation, glucosamine hydrochloride or a placebo was administered by NG intubation. Plasma samples were collected at baseline and 5, 15, 30, 60, 120, 360, 480 and 720 min after dosing. Synovial fluid (SF) samples were collected within 48 h before dosing and 1, 6 and 12h post-dosing. Glucosamine was analyzed by Liquid Chromatography Electrospray Tandem Mass Spectrometry (LC-ESI/MS/MS). Clinicopathological evaluation of SF parameters included white blood cell (WBC) count and total protein (TP) analyses.

RESULTS

No significant differences between groups were observed in SF baseline levels of WBC and TP at any stage of the study. SF WBC and TP significantly increased following IA LPS. The mean (+/-SD) maximal SF glucosamine levels (422.3+/-244.8 ng/mL) were significantly higher (>fourfold) in inflamed joints when compared to healthy joints (92.7+/-34.9 ng/mL). Glucosamine did not have any effect on standard SF parameters of inflammation.

CONCLUSION

Synovial inflammation leads to significantly higher synovial glucosamine concentrations compared to levels attained in healthy joints following oral administration of glucosamine hydrochloride. Whether these higher levels are translated into a therapeutic effect on the joint tissues remains to be elucidated.

Comparison of pharmacokinetics of glucosamine and synovial fluid levels following administration of glucosamine sulphate or glucosamine hydrochloride

OBJECTIVE

To compare the pharmacokinetics of glucosamine and the synovial fluid levels attained following treatment with glucosamine sulphate or glucosamine hydrochloride in a large animal model at clinically relevant doses.

METHODS

Eight adult female horses were used. Crystalline glucosamine sulphate (Dona) or glucosamine hydrochloride was administered at a dose of 20 mg/kg by either intravenous (i.v.) injection or nasogastric (n.g.) intubation. Plasma samples were collected before dosing and at 5, 15, 30, 60, 120, 360, 480 and 720 min after dosing. Synovial fluid samples were collected from the radiocarpal joints within 48 h before dosing and at 1, 6 and 12 h post-dosing. Glucosamine was assayed by Liquid Chromatography Electrospray Tandem Mass Spectrometry (LC-ESI/MS/MS).

RESULTS

Plasma concentrations reached approximately 50 microg/mL after i.v. injection and approximately 1 microg/mL after n.g. administration of both types of glucosamine. The median oral bioavailability was 9.4% for glucosamine sulphate and 6.1% for glucosamine hydrochloride. Synovial fluid concentrations were significantly higher at 1 and 6 h following oral treatment with glucosamine sulphate compared to glucosamine hydrochloride. Twelve hours following oral administration, glucosamine levels in the plasma and the synovial fluid were still significantly higher than baseline for the glucosamine sulphate preparation, but not for the hydrochloride preparation.

CONCLUSION

Following oral administration of a clinically recommended dose of glucosamine sulphate (Dona), significantly higher synovial fluid concentrations of glucosamine are attained, when compared to an equivalent dose of glucosamine hydrochloride. Whether this difference is translated into a therapeutic effect on the joint tissues remains to be elucidated.

Influence of E. coli lipopolysaccharide induced fever on the plasma kinetics of cefepime in cross-bred calves

The pharmacokinetic behavior of cefepime was studied in healthy and febrile cross-bred calves after single intravenous administration (10 mg/kg). The fever was induced with E. coli lipopolysaccharide (1 microg/kg, IV). The drug concentration in plasma was detected by microbiological assay method using E. coli (MTCC 739) test organism. Pharmacokinetic analysis of disposition data indicated that intravenous administration data were best described by 2 compartment open model. At 1 min the concentration of cefepime in healthy and febrile animals were 55.3 +/- 0.54 microg/ml and 50.0 +/- 0.48 microg/ml, respectively and drug was detected up to 12 h. The elimination half-life of cefepime was increased from 1.26 +/- 0.01 h in healthy animals to 1.62 +/- 0.09 h in febrile animals. Drug distribution was altered by fever as febrile animals showed volume of distribution (0.27 +/- 0.02 L/kg) higher than normal animal (0.19 +/- 0.01 L/kg). Total body clearances in healthy and febrile animals were 104.4 +/- 2.70 and 114.2 +/- 1.20 ml/kg/h, respectively. To maintain minimum therapeutic concentration of 1 mug/ml, a satisfactory dosage regimen of cefepime in healthy and febrile cross-bred calves would be 15.5 mg/kg and 8.2 mg/kg body weight, respectively, to be repeated at 8 h intervals. The T>MIC values (8 h) of cefepime suggested that this agent is clinically effective in the treatment of various infections.

Evaluation of safety and pharmacokinetics of vancomycin after intraosseous regional limb perfusion and comparison of results with those obtained after intravenous regional limb perfusion in horses

OBJECTIVE

To evaluate the clinical effects and pharmacokinetics of vancomycin in plasma and synovial fluid after intraosseous regional limb perfusion (IORLP) in horses and to compare results with those obtained after IV regional limb perfusion (IVRLP).

ANIMALS

6 horses.

PROCEDURES

1 forelimb of each horse received vancomycin hydrochloride (300 mg in 60 mL of saline [0.9% NaCl] solution) via IORLP; the contralateral limb received 60 mL of saline solution (control). Solutions were injected into the medullary cavity of the distal portion of the third metacarpal bone. Synovial fluid from the metacarpophalangeal (MTCP) and distal interphalangeal (DIP) joints and blood were collected prior to perfusion and 15, 30, 45, 65, and 90 minutes after beginning IORLP, and synovial fluid from the MTCP joint only and blood were collected 4, 8, 12, and 24 hours after beginning IORLP. Plasma urea and creatinine concentrations and clinical appearance of the MTCP joint region and infusion sites were determined daily for 7 days. Results were compared with those of a separate IVRLP study.

RESULTS

Clinical complications were not observed after IORLP. Mean vancomycin concentration in the MTCP joint was 4 microg/mL for 24 hours after IORLP. Compared with IORLP, higher vancomycin concentrations were detected in the DIP joint after IVRLP. Compared with IVRLP, higher vancomycin concentrations were detected in the MTCP joint for a longer duration after IORLP.

CONCLUSIONS AND CLINICAL RELEVANCE

IORLP with 300 mg of vancomycin in a 0.5% solution was safe and may be clinically useful in horses. Intravenous and intraosseous routes may be better indicated for infectious processes in the DIP and MTCP joints, respectively.

Septic Arthritis, Tenosynovitis, and Infections of Hoof Structures

Infectious diseases of synovial and hoof structures in horses can be devastating to soundness and can result in life-threatening complications. Timely diagnosis and early aggressive treatment can result in successful outcomes and resumption of athletic careers; however, delays in recognition and therapy can be the most costly reasons for failure. Sterilization of affected compartments and tissues requires removal of microorganisms and compromised tissue. Debridement, lavage, and appropriate antimicrobial drug use are the most reliable avenues of treatment. Antimicrobial drugs can be administered by local, regional, and systemic routes. Lavage techniques and debridement typically require surgical manipulations.

Evaluation of safety and pharmacokinetics of vancomycin after intravenous regional limb perfusion in horses

OBJECTIVE

To evaluate clinical variables, regional concentrations, and pharmacokinetics of vancomycin in the synovial fluid of distal forelimb joints of horses after IV regional limb perfusion.

ANIMALS

6 horses.

PROCEDURE

Vancomycin was administered via IV regional limb perfusion to the distal portion of the forelimbs of anesthetized horses. Drug (300 mg of vancomycin hydrochloride in 60 mL of saline [0.9% NaCl] solution) was infused into 1 forelimb, whereas the contralateral limb served as a control and was perfused with 60 mL of saline solution. Solutions were injected into the lateral digital vein after digital exsanguination. Synovial fluid from the metacarpophalangeal (MTCP) and distal interphalangeal (DIP) joints and systemic blood were collected prior to perfusion and 15, 30, 45, 65, and 90 minutes after initiation of the infusion. Synovial fluid from the MTCP joint and blood were also obtained at 4, 8, 12, and 24 hours after infusion. Plasma urea and creatinine concentrations, degree of lameness, and certain clinical variables involving the MTCP joint and infusion site were assessed for 7 days. Results were compared between the vancomycin treatment and control groups.

RESULTS

No complications or significant differences in renal function, lameness, or clinical variables were observed between groups. Vancomycin concentrations exceeded 4 microg/mL in MTCP joints for approximately 20 hours. Higher concentrations were reached in DIP joints than in MTCP joints.

CONCLUSIONS AND CLINICAL RELEVANCE

IV regional limb perfusion with 300 mg of vancomycin as a 0.5% solution was safe and may be useful in horses as treatment for distal limb infections.

The effect of endotoxin and dexamethasone on enrofloxacin pharmacokinetic parameters in swine

The impact of Escherichia coli-derived lipopolysaccharide (LPS) on the pharmacokinetic parameters of enrofloxacin in swine was assessed to determine whether this model would substitute for a pleuropneumonia infection model for pharmacokinetic evaluation of drugs. All animals received a single i.v. dose of enrofloxacin (5 mg/kg). Half the animals also received dexamethasone (0.5 mg/kg) to determine the impact of inflammation on any changes in enrofloxacin pharmacokinetics, as most of the effects of LPS are due to elaboration of inflammatory mediators. Administration of LPS alone (2.0 microg/kg) was associated with a decrease in clearance of enrofloxacin. Volume of distribution at steady state was increased in the dexamethasone-treated animals. The terminal elimination half-life of enrofloxacin was significantly increased in the LPS group. Dexamethasone administration, either alone or in combination with LPS challenge, increased the volume of distribution both at steady state and during the elimination phase. Lipopolysaccharide challenge did not affect the volume of distribution. Lipopolysaccharide challenge did not affect urinary excretion of enrofloxacin but did increase the urinary excretion of its principal metabolite, ciprofloxacin. However, the increased excretion did not begin until 24 h after administration of enrofloxacin. Because these pharamcokinetic results are different from those obtained with the pleuropneumonia model using the bacteria Actinobacillus pleuropneumoniae, the results of this study demonstrate that LPS is not a generic substitute for infection for the pharmacokinetic evaluation of drugs.

Pharmacokinetics of amoxycillin in normal horses and horses with experimental arthritis

The serum and synovial pharmacokinetics of amoxycillin (AMX) were studied after i.v. administration at a dosage of 40 mg/kg to normal horses and horses with induced aseptic carpal arthritis. The best estimates of serum and synovial pharmacokinetic parameters were calculated by mono or bivariable non-linear regression analysis. A biexponential equation was used to describe the concentration vs. time profiles in both normal and arthritic horses. There were no serum kinetic differences between normal and arthritic horses. There were, however, major synovial kinetic changes between these groups. The rate of penetration from serum to synovial fluid was larger in arthritic animals, indicating better penetration in this case. On the other hand, the rate of disappearance from synovial fluid was larger in normal horses, indicating more persistence of the drug in the diseased joint. Synovial AMX availability increased from 21% in normal horses to 79% in arthritic horses. These findings support the use of AMX for the treatment of infectious synovial joint disease produced by susceptible organisms in horses.

Clinical efficacy of ampicillin, pivampicillin and procaine penicillin G in a soft tissue infection model in ponies

Tissue chambers, implanted subcutaneously in ponies, were inoculated with Streptococcus zooepidemicus. The animals received either no antibiotics or one of the following treatments: pivampicillin per os (19.9 mg/kg, equivalent to 15 mg/kg ampicillin, every 12 h) for 7 or 21 days (7 and 5 ponies, respectively), procaine penicillin G intramuscularly (12 mg/kg = 12,000 IU/kg, every 24 h) for 7 days (7 ponies), or ampicillin sodium intravenously (equivalent to 15 mg/ kg ampicillin, every 8 h) for 1 day (5 ponies). Only intravenous administration was started before infection (prophylactically), the other treatments were started 20 h after infection (curatively). A total of 7 ponies received no antibiotics. In untreated controls, the infection led to abscessation of the tissue chamber in 4 to 10 days. Curative treatment with either pivampicillin or procaine penicillin G for 7 days resulted in a reduction of viable bacteria in the tissue chamber but did not eliminate the infection, resulting in abscessation in 5 to 14 days. However, administration of pivampicillin for 21 days eliminated the streptococci in five out of five ponies and prophylactic administration of ampicillin was successful in three out of five ponies.

Experimentally-induced synovitis as a model for acute synovitis in the horse

The use of extremely small dosages of intra-articular E. coli lipopolysaccharide (LPS) endotoxin can create a model of synovitis that mimics acute synovitis in horses. Dosages of 5000 ng, 25 ng, 0.5 ng, 0.25 ng, 0.17 ng and 0.125 ng per joint were injected into various joints of a total of 6 horses. The dose response of LPS on clinical signs and synovial fluid parameters was evaluated at baseline and 12, 24, 36 and 48 h after LPS injection. Peripheral venous blood analysis was performed at baseline and at 0, 4, and 12 h after LPS injection. Dosages greater than 0.5 ng/joint resulted in clinical signs of endotoxaemia including fever, depression, inappetence and non-weightbearing lameness. Although the total peripheral venous leucocyte count was not decreased at any dosage, the 5000 ng/joint dosage of LPS altered venous leucocyte differential resulting in an increase in the number of segmented and band neutrophils with a concomitant decrease in lymphocytes. Synovial fluid total nucleated cell count (TNC) and total protein (TP) was linearly responsive to increases in intra-articular LPS dosages up to the 0.5 ng/joint dose. At dosages of LPS > 0.5 ng, synovial fluid mean +/- s.e.m. TNC and TP were 122.0 +/- 27 x 10(9) cells/l and 59.3 +/- 1.7 milligrams respectively, at 12 h after injection. This may represent the maximal response of the joint to increased concentrations of LPS endotoxin over 0.5 ng/joint.(ABSTRACT TRUNCATED AT 250 WORDS)

Ampicillin and its congener prodrugs in the horse

Ampicillin is an antibiotic commonly administered to horses by both the intramuscular (i.m.) and the intravenous (i.v.) route. Its physicochemical properties restrict its absorption after oral administration and explain its rapid elimination from the body. To prolong the effects of ampicillin in the horse, attempts have been made to alter its elimination and absorption rates. The alteration of urinary pH did not change the plasma disposition of the antibiotic but when probenecid was administered concurrently with ampicillin, a significant reduction of total body clearance was achieved. Ampicillin may also be maintained in the equine body, for a prolonged period of time when administered as an i.v. infusion. However, the practical difficulties associated with this route of administration and the limited potential advantage over conventional routes such as i.m. injection restrict its application to the critically ill animal and the perioperative period. When bacampicillin and pivampicillin (two ampicillin prodrugs) were administered to horses, high oral bioavailability was obtained, and the use of prodrugs commands the need for further investigation. The use of ampicillin might be limited in the future as an increase in the number of resistant equine bacterial strains emerge and it may be prudent to restrict its use according to the principles of good clinical pharmacological practice.

Pharmacokinetic values of drugs frequently used in performance horses

Tables of values of pharmacokinetic variables (volume of distribution, total body clearance, and plasma elimination half-life) of drugs frequently administered to performance horses are accompanied by explanatory notes. Drugs described include the nonsteroidal anti-inflammatory drugs, corticosteroids, anabolic steroids, central nervous system-modifying drugs, respiratory system drugs, diuretics, local anesthetics, and antibacterial drugs.

Distribution of oxytetracycline to tissue cages and granuloma pouches in calves and effect of acute inflammation on distribution to tissue cages

The effect of acute inflammation on oxytetracycline (OTC) distribution was studied in a tissue cage model in calves. An acute inflammatory reaction was induced in tissue cages by injecting lipopolysaccharide (LPS) from Salmonella typhimurium. The distribution of OTC to tissue cage fluid (TCF) was also compared with distribution to fluid from granuloma pouches (GPF). Tissue from LPS-injected cages showed histological changes indicating an acute inflammatory reaction. Concentrations of OTC were higher in LPS cages than in controls; at 1, 2, 4 and 10 h the difference was statistically significant (P less than 0.05). Numerically the overall elimination rate constant (kel) was larger, elimination half-life (t1/2) shorter, peak concentration (Cmax) higher, and time of peak concentration (Tmax) shorter in LPS cages than in controls. The area under the curve (AUC) of OTC was greater and the ratio AUCTCF/AUCserum was higher in LPS cages than in controls. Although statistically significant differences were not found for all the pharmacokinetic parameters, it was concluded that distribution to and elimination from LPS cages were both faster than in controls. Concentration-time profiles of OTC were similar in TCF and GPF in that concentrations were lower and elimination was more prolonged than in serum. Levels were higher in GPF than in TCF up to 3 h after injection; thereafter the relationship was reversed. Distribution to and elimination processes from GPF appeared to be faster than from TCF as numerically kel was higher, t1/2 shorter and Tmax shorter in GPF than in TCF. It was concluded that the granuloma pouch model and the tissue cage model have similarities in distribution and elimination patterns and that differences are most probably due to differences in the ratio of the surface area to the volume.

Antibiotics in the treatment of wounds

In selecting an antibiotic, considerations include the sensitivity of the pathogen, drug distribution to the site of infection, bacteriostatic or bactericidal action under the existing tissue conditions, safety, and cost. Ideally, in vitro susceptibility of the pathogen can be obtained. In addition, cytologic evaluation, including a Gram stain, may be helpful in directing the initial course of therapy. Antibiotic sensitivity does not by itself guarantee satisfactory results. The terms "sensitive" and "resistant" are relative terms based on achievable blood levels of antimicrobial agents. The term "sensitive" implies that the level necessary to inhibit bacterial growth is achieved when an adequate dose is given at appropriate intervals. The distribution of the drug and, in turn, the level achieved at the site of infection depends on a number of factors, including molecular size, protein binding, and lipid solubility. Because, in most cases, specific tissue concentrations are not known, serum concentrations are used to represent the levels in the extracellular fluid space, which is the site of most bacterial infections. The local environment can further enhance or hinder antimicrobial penetration and activity. The antibiotic concentration achieved in the blood affects the concentration at the site of infection because simple passive diffusion appears to be the method of transport for most antibiotics. The antibiotic activity after reaching the site of infection is influenced by environmental conditions. Local production of enzymes, purulent and fibrinous exudate, and pH changes can adversely affect drug action. With many of these variables being difficult to predict, knowledge of etiologic agents is the cornerstone of rational use of the antimicrobial drugs. A reasonable suspicion based on clinical signs and knowledge of likely pathogens can guide the initial choice of antimicrobial therapy. Since both aerobic and anaerobic organisms may be involved in wound infections, and because antibiotic sensitivity of many of these pathogens is unpredictable, broad-spectrum antimicrobial therapy is often warranted initially.