Jonathan N. King

Preclinical pharmacology of robenacoxib: a novel selective inhibitor of cyclooxygenase‐2

This manuscript reports the results of preclinical studies in the rat with robenacoxib, a novel selective cyclooxygenase (COX)-2 inhibitor. Robenacoxib selectively inhibited COX-2 in vitro as evidenced from COX-1:COX-2 IC50 ratios of 27:1 in purified enzyme preparations and >967:1 in isolated cell assays. Binding to COX-1 was rapid and readily reversible (dissociation t(1/2) << 1 min), whilst COX-2 binding was slowly reversible (t(1/2) = 25 min). In vivo, robenacoxib inhibited PGE2 production (an index of COX-2 inhibition) in lipopolysaccharide (LPS)-stimulated air pouches (ID50 0.3 mg/kg) and for at least 24 h in zymosan-induced inflammatory exudate (at 2 mg/kg). Robenacoxib was COX-1 sparing, as it inhibited serum TxB2 synthesis ex vivo (an index of COX-1 inhibition) only at very high doses (100 mg/kg but not at 2-30 mg/kg). Robenacoxib inhibited carrageenan-induced paw oedema (ID50 0.40-0.48 mg/kg), LPS-induced fever (ID50 1.1 mg/kg) and Randall-Selitto pain (10 mg/kg). Robenacoxib was highly bound to plasma protein (99.9% at 50 ng/mL in vitro). After intravenous dosing, clearance was 2.4 mL/min/kg and volume of distribution at steady-state was 306 mL/kg. Robenacoxib was preferentially distributed into inflammatory exudate; the AUC for exudate was 2.9 times higher than for blood and the MRT in exudate (15.9 h) was three times longer than in blood (5.3 h). Robenacoxib produced significantly less gastric ulceration and intestinal permeability as compared with the reference nonsteroidal anti-inflammatory drug (NSAID), diclofenac, and did not inhibit PGE2 or 6-keto PGF(1alpha) concentrations in the stomach and ileum at 30 mg/kg. Robenacoxib also had no relevant effects on kidney function at 30 mg/kg. In summary, results of preclinical studies in rats studies suggest that robenacoxib has an attractive pharmacological profile for potential use in the intended target species, cats and dogs.

Use of a pharmacokinetic/pharmacodynamic approach in the cat to determine a dosage regimen for the COX-2 selective drug robenacoxib

This study investigated the analgesic, anti-inflammatory and antipyretic efficacy of the new COX-2 selective inhibitor robenacoxib in the cat and established pharmacodynamic (PD) parameters for these effects. Robenacoxib, at a dosage of 2 mg/kg administered subcutaneously, was evaluated in a kaolin-induced paw inflammation model in 10 cats, using both clinically relevant endpoints (lameness scoring, locomotion tests) and other indicators of inflammation (body and skin temperature, thermal pain threshold) to establish its pharmacological profile. A pharmacokinetic/pharmacodynamic (PK/PD) modelling approach, based on indirect response models, was used to describe the time course and magnitude of the responses to robenacoxib. All endpoints demonstrated good responsiveness to robenacoxib administration and both the magnitude and time courses of responses were well described by the indirect pharmacodynamic response models. Pharmacokinetic and clinically relevant pharmacodynamic parameters were used to simulate dosage regimens that will assist the planning of clinical trials and the selection of an optimal dosage regimen for robenacoxib in the cat.

Analytical determination and pharmacokinetics of robenacoxib in the dog

An analytical method was developed and validated for the measurement of the novel analgesic and anti-inflammatory drug robenacoxib in blood and plasma of dogs and cats. To prevent nonreproducible carry-over effects, an initial solid phase extraction procedure was followed by high pressure liquid chromatography analysis for samples with concentrations in the range 500 to 20,000 ng/mL. To improve accuracy, samples of concentration 3 to 100 ng/mL were analyzed by liquid chromatography-mass spectrometry. Applying these methods, blood concentration-time profiles and pharmacokinetic variables of robenacoxib in dogs were determined in a four-phase cross-over study, which compared different routes of administration of the drug, including intravenous (i.v.) injection, oral application with and without feed, and subcutaneous (s.c.) application. After i.v. administration the mean clearance from blood was 0.81 L/kg/h, the volume of distribution was 0.77 L/kg for the elimination phase and 0.24 L/kg for steady-state, and the terminal half-life in blood was 0.63 h. Maximum blood concentrations were obtained in less than 1 h following oral or s.c. application. Absolute bioavailability was 88% after s.c. injection, 84% after oral administration to fasted dogs, but was reduced to 62% when applied orally to fed dogs. In canine and feline plasma the degree of binding of robenacoxib to plasma protein in vitro was greater than 98%. The blood:plasma concentration ratio was 0.44:1 in the dog and 0.65:1 in the cat. In conclusion analytical methods for the quantification of robenacoxib in blood and plasma in the dog and cat were developed and validated. In dogs, robenacoxib has good bioavailability after oral (84%) and subcutaneous (88%) administration.

In vitro and ex vivo inhibition of canine cyclooxygenase isoforms by robenacoxib: a comparative study.

In vitro whole blood canine assays were used to quantify the inhibitory actions of the novel non-steroidal anti-inflammatory drug (NSAID) robenacoxib on the cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, in comparison with other drugs of the NSAID class. COX-1 activity was determined by measuring serum thromboxane (Tx)B(2) synthesis in blood samples allowed to clot at 37 degrees C for 1h. COX-2 activity was determined by measuring prostaglandin (PG)E(2) synthesis in blood samples incubated at 37 degrees C for 24h in the presence of lipopolysaccharide. The rank order of selectivity for inhibition of COX-2 versus COX-1 (IC(50) COX-1:IC(50) COX-2) for veterinary drugs was highest with robenacoxib (128.8) compared to deracoxib (48.5), nimesulide (29.2), S+ carprofen (17.6), meloxicam (7.3), etodolac (6.6), R- carprofen (5.8) and ketoprofen (0.88). Selectivity expressed as the clinically relevant ratio IC(20) COX-1:IC(80) COX-2 was highest for robenacoxib (19.8) compared to deracoxib (2.3), S+ carprofen (2.5), R- carprofen (2.1), nimesulide (1.8), etodolac (0.76), meloxicam (0.46) and ketoprofen (0.21). An in vivo pharmacokinetic ex vivo pharmacodynamic study in the dog established dosage and concentration-effect relationships for single oral doses of robenacoxib over the dosage range 0.5-8.0mg/kg. Values of C(max) and AUC were linearly related to dosage over the tested range. Robenacoxib did not inhibit serum TxB(2) synthesis (COX-1) ex vivo at dosages of 0.5-4.0mg/kg and produced only transient inhibition (at the 1h and 2h sampling times) at the 8mg/kg dosage. All dosages of robenacoxib (0.5-8mg/kg) produced marked, significant and dose related inhibition of PGE(2) synthesis (COX-2) ex vivo. The data demonstrate that in the dog robenacoxib is a highly selective inhibitor of the COX-2 isoform of COX, and significantly inhibits COX-2 and spares COX-1 in vivo when administered orally over the dosage range 0.5-4.0mg/kg.

Differential inhibition of cyclooxygenase isoenzymes in the cat by the NSAID robenacoxib.

Robenacoxib is a new nonsteroidal anti-inflammatory drug (NSAID) developed for use in companion animal medicine. The objectives of this study were: to quantify the inhibitory actions of robenacoxib on cyclooxygenase (COX) isoenzymes in feline whole blood assays; to establish blood concentration-time profiles of robenacoxib after intravenous and subcutaneous dosing in the cat and; to predict the time courses of inhibition of COX isoforms by robenacoxib. COX-1 and COX-2 activities in heparinized feline whole blood samples were induced with calcium ionophore and lipopolysaccharide, respectively. Inhibition of thromboxane B2 provided a marker of both COX-1 and COX-2 activities and a nonlinear parametric mixed effects modelling approach was used to establish the pharmacodynamic parameters describing this inhibition. Mean values (and prediction intervals) of IC50 were 28.9 (16.4-51.1) microM (COX-1) and 0.058 (0.010-0.340) microM (COX-2). These parameters were used to compute several selectivity indices. Selectivity IC ratios (COX-1:COX-2) were 502.3 (IC50/IC50), 451.6 (IC95/IC95) and 17.05 (IC20/IC80). Based on a clinically recommended dosage regimen of 2 mg/kg, it was predicted that the corresponding mean robenacoxib blood concentration over the first 12 h after drug administration corresponded to 5% inhibition of COX-1 and 90% inhibition of COX-2.

Evaluation of the Clinical Efficacy of Benazepril in the Treatment of Chronic Renal Insufficiency in Cats

BACKGROUND Chronic renal insufficiency (CRI) is a common disease in cats. Angiotensin-converting enzyme inhibitors (ACEI) have beneficial effects in humans with CRI by reducing the loss of protein in the urine and increasing life expectancy. HYPOTHESIS The ACEI benazepril has beneficial effects on survival, clinical variables, or both as compared with placebo in cats with CRI. ANIMALS 61 cats with naturally occurring CRI. METHODS The cats were enrolled into a prospective, randomized, double-blind, placebo-controlled clinical trial. Cats received placebo or 0.5-1 mg/kg benazepril once daily for up to 6 months. RESULTS Urine protein/urine creatinine ratios were significantly (P < .05) lower with benazepril as compared with placebo at days 120 and 180. Three cats with placebo and 1 cat with benazepril were removed prematurely from the study because of deterioration of CRI or death. Cats were classified into 4 stages of CRI according to the International Renal Interest Society (IRIS) classification scheme. Incidence rates of cats with IRIS classification stage 2 or stage 3 that remained in stage 2 or 3 without progressing to stage 4 were higher with benazepril (93 +/- 5%) as compared with placebo (73 +/- 13%). CLINICAL IMPORTANCE These results suggest a potential for benazepril to delay the progression of disease, extend survival time, or both in cats with CRI.

Evaluation of subcutaneous and oral administration of robenacoxib and meloxicam for the treatment of acute pain and inflammation associated with orthopedic surgery in dogs

OBJECTIVE To assess efficacy and tolerability of robenacoxib for control of pain and inflammation in dogs undergoing orthopedic surgery. ANIMALS 140 client-owned dogs. PROCEDURES A multicenter, prospective, randomized, blinded field trial was conducted to compare robenacoxib (97 dogs) and meloxicam (43 dogs). After randomization, each dog received an initial dose (robenacoxib, 2 mg/kg; meloxicam, 0.2 mg/kg) via SC injection before surgery and daily doses (robenacoxib, 1 to 2 mg/kg; meloxicam, 0.1 mg/kg) administered orally for up to 15 days after surgery. Efficacy was assessed by veterinarians and owners via numeric rating scales and visual analogue scales. Safety was assessed on the basis of reported adverse events, clinical signs, results of hematologic and biochemical analyses, and buccal mucosa bleeding times. RESULTS Treatment groups were balanced with respect to baseline and demographic data. Both treatments provided similar adequate pain control, as assessed with a modified Glasgow pain scale as the primary end point and supported by secondary end points in evaluations conducted by veterinarians and owners. For the primary end point, the ratio of the reciprocal of the scores for robenacoxib to meloxicam was 1.16 (95% confidence interval, 0.98 to 1.37). No dogs required rescue analgesia. Both treatments were associated with only minor adverse events, which were not necessarily related to the administered treatments and did not affect mucosal bleeding times. CONCLUSIONS AND CLINICAL RELEVANCE Robenacoxib provided efficacy and tolerability similar to those of meloxicam for the management of perioperative pain and inflammation in dogs undergoing orthopedic surgery.

Robenacoxib vs. carprofen for the treatment of canine osteoarthritis; a randomized, noninferiority clinical trial

Robenacoxib is a member of the coxib class of nonsteroidal anti-inflammatory drugs (NSAID), with high selectivity for the cyclooxygenase (COX)-2 isoform of COX. In this study, the efficacy and tolerability of robenacoxib were compared with those of carprofen in canine osteoarthritis in a multi-centre, prospective, randomized, blinded, positive-controlled noninferiority clinical trial. Both drugs were administered orally once daily at recommended dosages: robenacoxib at 1-2 mg/kg (n = 125 dogs) and racemic carprofen at 2-4 mg/kg (n = 63 dogs) for a total of 12 weeks. The efficacy of the test compounds was assessed by veterinary investigators and owners using numerical rating scales at baseline and days 7, 14, 28, 56 and 84. In both groups, all scores were significantly (P < 0.0001) improved compared with baseline at all time points (days 7-84). Robenacoxib had noninferior efficacy to carprofen for the primary endpoint, the global functional disability, both for all dogs and for the subgroup of dogs in which robenacoxib was not administered during meals. Noninferiority was also demonstrated for three of six veterinary investigator secondary endpoints and four of six owner efficacy endpoints. For haematology and clinical chemistry variables, there were some significant differences from baseline levels but no differences between groups. There were no differences between groups in the frequencies of adverse events, which were reported in 46% dogs with robenacoxib and 52% with carprofen (P = 0.44), which were most frequently mild events affecting the gastrointestinal tract. In conclusion, noninferior efficacy and tolerability of robenacoxib compared with carprofen was demonstrated in dogs with osteoarthritis.

Effects of benazepril in the treatment of feline hypertrophic cardiomyopathy Results of a prospective, open-label, multicenter clinical trial.

OBJECTIVES To evaluate the efficacy of benazepril on clinical signs and echocardiographic parameters in cats with primary hypertrophic cardiomyopathy (HCM). BACKGROUND ACE-inhibitors have positive effects in man with HCM, and contribute to a reduction of myocardial hypertrophy. Addition of an ACE-inhibitor to the standard treatment of HCM in cats may have beneficial effects. METHODS A total of 32 cats which were either asymptomatic or in stabilised congestive heart failure (ISACHC* class Ib, II or IIIa) were included in a one-year, prospective, open-label, clinical trial in 5 centres in Switzerland. 28 of these cats were allocated to one of two treatment groups: 1) standard therapy (ST) alone (n=9), consisting of a long-acting formulation of diltiazem (6-9 mg/kg sid) and optional acetylsalicylic acid (50 mg twice weekly, or 2) the same ST plus benazepril (0.33 - 0.75 mg/kg sid, n=19). RESULTS Cats treated with benazepril showed a statistically significant decrease (mean +/- SEM, 0.11 +/- 0.03 mm/month, p = 0.002) in the left ventricular wall thickness (LVWD) from baseline, while no change (increase of 0.02 +/- 0.04 mm/month, p=0.66) was observed in cats on ST alone. Differences in LVWD between the two groups reached statistical significance (p=0.02). Benazepril treated cats showed more improvement in clinical signs (20-53%) than cats receiving ST alone (0-20%) but differences between the groups were not statistically significant (p>0.1). No change in septal thickness (IVSD) or left atrial to aortic root ratio (LA/Ao) was observed in either group. CONCLUSIONS Benazepril had some beneficial effects on clinical signs and cardiac remodelling in cats with HCM and was well tolerated. These results, however, need to be confirmed in additional controlled studies. * ISACHC classification is described in the previous paper (Bench-study).

Comparison of injectable robenacoxib versus meloxicam for peri-operative use in cats: Results of a randomised clinical trial

The objective of this study was to evaluate the efficacy and tolerability of robenacoxib, a selective cyclooxygenase-2 inhibitor, for the treatment of post-operative pain and inflammation in cats. The study was a prospective, multi-centre, randomised, blinded, non-inferiority design clinical study to compare robenacoxib to meloxicam. Ninety-six cats undergoing surgery at eight centres in Japan were allocated randomly to receive a single s.c. injection of robenacoxib (2 mg/kg, n=67) or meloxicam (0.3 mg/kg, n=29) shortly before induction of anaesthesia. Most cats underwent soft tissue surgery (n=87), mainly ovariectomy (n=68). Post-operative pain and inflammation were assessed at 3, 8 and 22 h after recovery from anaesthesia using numerical rating scales. For the primary efficacy endpoint (total clinician score), robenacoxib had significantly better efficacy than meloxicam, the relative efficacy ratio being 1.47 (95% confidence interval 1.19-1.78, P=0.0003). For the secondary efficacy endpoints, robenacoxib was superior to meloxicam when assessed on the basis of posture, behaviour, pain on palpation and overall pain control, while meloxicam was superior with respect to wound heat. No cat in either group required rescue analgesia therapy. In tolerability assessments, pain during injection and pain and inflammation at the injection site 22 h after recovery from anaesthesia were rated significantly less with robenacoxib compared to meloxicam. Both treatments were well tolerated on the basis of clinical observations and blood tests, with no significant differences between groups. In conclusion, single pre-operative administration of robenacoxib was well tolerated and had superior efficacy to meloxicam in reducing post-operative pain in cats.