OBJECTIVE To evaluate pharmacokinetic and pharmacodynamic characteristics of 3 doses of tapentadol hydrochloride orally administered in dogs. ANIMALS 6 healthy adult mixed-breed dogs. PROCEDURES In a prospective, randomized crossover study, dogs were assigned to receive each of 3 doses of tapentadol (10, 20, and 30 mg/kg, PO); there was a 1-week washout period between subsequent administrations. Plasma concentrations and physiologic variables were measured for 24 hours. Samples were analyzed by use of high-performance liquid chromatography–tandem mass spectrometry. RESULTS Tapentadol was rapidly absorbed after oral administration. Mean maximum plasma concentrations after 10, 20, and 30 mg/kg were 10.2, 19.7, and 31 ng/mL, respectively. Geometric mean plasma half-life of the terminal phase after tapentadol administration at 10, 20, and 30 mg/kg was 3.5 hours (range, 2.7 to 4.5 hours), 3.7 hours (range, 3.1 to 4.0 hours), and 3.7 hours (range, 2.8 to 6.5 hours), respectively. Tapentadol and its 3 quantified metabolites (tapentadol sulfate, tapentadol-O-glucuronide, and desmethyltapentadol) were detected in all dogs and constituted 0.16%, 2.8%, 97%, and 0.04% of the total area under the concentration-time curve (AUC), respectively. Plasma AUCs for tapentadol, tapentadol sulfate, and tapentadol-O-glucuronide increased in a dose-dependent manner. Desmethyltapentadol AUC did not increase in a linear manner at the 30-mg/kg dose. Sedation scores and heart and respiratory rates were not significantly affected by dose or time after administration. CONCLUSIONS AND CLINICAL RELEVANCE Oral administration of tapentadol was tolerated well, and the drug was rapidly absorbed. Adverse events were not apparent in any dogs at any doses in this study.

The aim of this study was to determine the pharmacokinetics of amikacin and penicillin G sodium when administered in combination as an intravenous regional limb perfusion (IVRLP) to horses. Seven healthy adult horses underwent an IVRLP in the cephalic vein with 2 g of amikacin sulfate and 10 mill IU of penicillin G sodium diluted to 60 mL in 0.9% saline. A pneumatic tourniquet set at 450 mmHg was left in place for 30 min. Synovial fluid was collected from the metacarpophalangeal joint 35 min and 2, 6, 12, and 24 h after infusion of the antimicrobials. Concentrations of amikacin and penicillin in synovial fluid were quantitated by liquid chromatography tandem-mass spectrometry analysis. Therapeutic concentrations of amikacin and penicillin for equine-susceptible pathogens were achieved in the synovial fluid. Maximum synovial concentrations (Cmax) (mean ± SE) for amikacin and penicillin were 132 ± 33 μg/mL and 8474 ± 5710 ng/mL, respectively. Only 3 horses had detectable levels of penicillin at 6 h and 1 at the 12 h sample. The combination of amikacin with penicillin G sodium via IVDLP resulted in reported therapeutic concentrations of both antibiotics in the synovial fluid. The Cmax:MIC (minimum inhibitory concentration) ratio for amikacin was 8:1 and Time > MIC for penicillin was 6 h. At 24 h, the mean concentration of amikacin was still above 4 μg/mL. Terminal elimination rate constants (T1/2 lambdaz) were 13.6 h and 2.8 h for amikacin and penicillin, respectively. The use of IVDLP with penicillin may therefore not be practical as rapid clearance of penicillin from the synovial fluid requires frequent perfusions to maintain acceptable therapeutic concentrations.

OBJECTIVE To evaluate the effect of volume of IV regional limb perfusion (IVRLP) on amikacin concentrations in synovial and interstitial fluid of horses. ANIMALS 8 healthy adult horses. PROCEDURES Each forelimb was randomly assigned to receive IVRLP with 4 mL of amikacin sulfate solution (250 mg/mL) plus 56 mL (total volume, 60 mL) or 6 mL (total volume, 10 mL) of lactated Ringer solution. Horses were anesthetized, and baseline synovial and interstitial fluid samples were collected. A tourniquet was placed, and the assigned treatment was administered via the lateral palmar digital vein. Venous blood pressure in the distal portion of the limb was recorded. Additional synovial fluid samples were collected 30 minutes (just before tourniquet removal) and 24 hours after IVRLP began; additional interstitial fluid samples were collected 6 and 24 hours after IVRLP began. RESULTS 30 minutes after IVRLP began, mean amikacin concentration in synovial fluid was significantly greater for the large-volume (459 μg/mL) versus small-volume (70 μg/mL) treatment. Six hours after IVRLP, mean concentration in interstitial fluid was greater for the large-volume (723 μg/mL) versus small-volume (21 μg/mL) treatment. Peak venous blood pressure after large-volume IVRLP was significantly higher than after small-volume IVRLP, with no difference between treatments in time required for pressure to return to baseline. CONCLUSIONS AND CLINICAL RELEVANCE Study findings suggested that large-volume IVRLP would deliver more amikacin to metacarpophalangeal joints of horses than would small-volume IVRLP, without a clinically relevant effect on local venous blood pressure, potentially increasing treatment efficacy.

Holstein steers were fed carbohydrate-rich, short-fiber basal diets with and without added sodium sulfate. Steers fed the high-sulfate diet developed the CNS disorder polioencephalomalacia (PEM). The onset of signs of PEM was associated with increased sulfide concentration in the rumen fluid. Over the course of the disease, anaerobic rumen bacteria were enumerated in roll tubes by use of the Hungate method to determine the effect of dietary sulfate on sulfate-reducing bacterial numbers. Media used included a general type for total counts and sulfate-containing media with and without cysteine to assess sulfate-reducing bacteria. Changes in total and sulfate-reducing bacterial numbers attributable to dietary sulfate content were not observed. The capacity to generate hydrogen sulfide from sulfate in fresh rumen fluid in vitro was substantially increased only after steers had been fed the high-sulfate diet for 10 to 12 days, which coincided with the onset of signs of PEM. The low capacity for hydrogen sulfide production of rumen fluid taken at earlier times in the feeding period suggests that rumen microorganisms must adapt to higher dietary sulfate content before they are capable of generating potentially toxic concentrations of sulfide.

To study their role in sulfate reduction, anaerobic bacteria were cultured from rumen fluid samples of cattle fed high-carbohydrate, short-fiber diets with and without added sulfate. The steers fed the diet with added sulfate developed polioencephalomalacia. Microbiological methods included colony-type profiles, molybdate sensitivity, presence of desulfoviridin, sulfate reduction rates of pure and mixed cultures, and incubation time effects on sulfate reduction. Colony-type profiles indicated decreased diversity, but no relative change in numbers of sulfate-reducing bacteria in rumen fluid from cattle fed diets with and without added sulfate. Thirteen bacterial isolates were selected for further study on the basis of colony type, sulfate-reducing activity, and growth in lactate, sulfate, and yeast extract media. Seven of the isolates had Desulfovibrio-like characteristics (ie, they were gram-negative, motile rods that reduced sulfate, were inhibited by molybdate, and contained the pigment desulfoviridin). The remaining 6 isolates were gram-negative, nonmotile rods. Four of these released sulfide from cysteine, and 2 generated only limited amounts of sulfide from sulfate or cysteine. The 7 sulfate-reducing isolates generated sulfide in rumen fluid broth medium at greater rates than those observed in fresh rumen fluid. Sulfate reduction could be sustained in cultures for prolonged incubation times if the gas phase containing hydrogen sulfide was replaced at frequent intervals. Variations in the amount of sulfate reduced by the pure cultures were most pronounced at short incubation times. Sulfate reduction was not inhibited in mixed cultures of sulfate-reducing and nonsulfate-reducing bacteria.

The effect of interleukin 1 (IL-1) on equine articular cartilage was investigated, using a cartilage explant culture system. Measurement of [35S]O4 incorporation revealed synthesis of matrix proteoglycan by cartilage to be decreased 45, 59.7, and 37.5% after 1, 3, and 5 days, respectively, in culture in the presence of 5 U of IL-1/ml. There was no change in proteoglycan degradation as determined by measurement of [35S]O4 release into the culture medium. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cartilage-conditioned medium indicated that exposure of cartilage to IL-1 caused a decrease in total protein synthesis by 45, 68, and 87% after 1, 3, and 5 days, respectively, in culture while selectively inducing synthesis of the 57-kd neutral metalloproteinase stromelysin (matrix metalloproteinase-3) in young and adult horses. Identification of stromelysin was confirmed by functional characterization and immunoprecipitation. Baseline total protein synthesis, as well as specific synthesis of stromelysin in cartilage from adult and aged horses, was markedly less than that of young horses. The IL-1-induced induced reduction in total protein synthesis may not be a characteristic of equine articular cartilage from affected joints of horses with naturally acquired osteoarthritis as indicated by an overall increase in protein synthesis by osteoarthritic explants. Introduction of IL-1 into an equine articular cartilage explant culture system resulted in decrease of matrix component synthesis and increase in specific degradative enzyme synthesis and activity. Articular cartilage from aged horses had markedly less overall metabolic activity, compared with cartilage from young horses. Articular cartilage from affected joints of horses with naturally acquired osteoarthritis did not have metabolic alterations identical to those of IL-1-stimulated normal articular cartilage from the same individual, necessitating reevaluation of the validity of the IL-1-induced model of osteoarthritis. Osteoarthritis is a common, naturally acquired disease of horses, and tissue from animals of all ages and stages of osteoarthritis is available. The equine model of osteoarthritis may afford an important means of studying the alterations in articular cartilage metabolism as a function of age and disease severity.

Two commercially available tests, an antigen-capture ELISA for use on fecal samples, and a peroral nylon string test for use in dogs, were compared with a zinc sulfate fecal concentration technique (ZSCT) for detection of giardiasis in dogs. Of 77 dogs and 164 fecal samples (from these dogs), 33 and 52, respectively were found to be Giardia-positive on the basis of results of the ZSCT. The ELISA gave false-negative results for 10 and 14% of ZSCT-positive dogs and fecal samples, respectively, and false-positive results (relative to the ZSCT test results) in 13 and 10% of ZSCT-positive dogs and fecal samples, respectively. Of the 18 string-tested dogs, 14 were positive by results of the ZSCT. Of the 4 dogs that were Giardia-negative by ZSCT, 2 were Giardia-positive by ELISA. Dogs were sedated and given water and metoclopramide to aid passage into the duodenum of the capsule containing a nylon string. Of the 21 string tests performed on the 18 dogs, only 5 strings reached the duodenum, and 0 of the 5 yielded positive results for Giardia sp. Because the string broke in 1 dog (leaving most in the gastrointestinal tract and, therefore, producing a risk of string foreign body) further string tests were not done.

Because articular chondrocytes are a target for drugs that can influence the integrity of cartilage, we investigated the effects of 3 antiarthritic drugs, glycosaminoglycan polysulfate, diclofenac-Na, and S-adenosylmethionine sulfate p-toluenesulfonate on total protein, fibronectin, and DNA synthesis, as well as on extradomain-A fibronectin and keratan sulfate content. Glycosaminoglycan polysulfate stimulated dose-dependent incorporation of [35S]methionine into protein and fibronectin, whereas incorporation of [3H]thymidine into DNA was unaffected. Total fibronectin, extradomain-A fibronectin, and keratan sulfate content were high in chondrocyte cultures treated with glycosaminoglycan polysulfate. In contrast, fibronectin and DNA synthesis, as well as extradomain-A fibronectin and keratan sulfate content were unaffected by diclofenac-Na. S-adenosylmethionine decreased dose-dependently the synthesis of fibronectin, as well as the content of fibronectin and keratan sulfate. At the highest concentration of S-adenosylmethionine tested, findings suggest that cell viability was impaired as assessed by the release of lactate dehydrogenase into the media.

Hexosamine concentration, DNA concentration, and [35S]sulfate incorporation for articular cartilage obtained from various sites in the metacarpophalangeal and carpal joints of horses were measured. The same measurements were made on the repair tissue filling full-thickness articular defects in the intermediate carpal bone and on cartilage surrounding partial-thickness defects 6 weeks after the defects were created arthroscopically. Cellularity (measured as DNA concentration), proteoglycan content (measured as hexosamine concentration), and proteoglycan synthesis (measured as [35S]sulfate incorporation) varied according to the site sampled. Cartilage from the transverse ridge of the head of the third metacarpal bone and the radial facet of the third carpal bone had the lowest hexosamine concentration, whereas rate of proteoglycan synthesis was lowest in cartilage from the transverse ridge of the head of the third metacarpal bone and the distal articular surface of the radial carpal bone. Repair tissue filling a full-thickness cartilage defect at 6 weeks was highly cellular. It was low in proteoglycan content, but was actively synthesizing these macromolecules. In contrast, the cartilage surrounding a partial-thickness defect was unchanged 6 weeks after the original defect was made.

OBJECTIVE To determine the median time to maximum concentration (tmax) 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 tmax 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 tmax 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.