Preliminary investigations into a novel, long-acting, injectable, intramuscular formulation of omeprazole in the horse

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1 Experimental and Basic Research Studies Preliminary investigations into a novel, long-acting, injectable, intramuscular formulation of omeprazole in the horse B. W. SYKES*, K. KATHAWALA, Y. SONG, S. GARG, S. W. PAGE, C. UNDERWOOD and P. C. MILLS School of Veterinary Science, University of Queensland, Gatton, Queensland, Australia Luoda Pharma Pty Ltd, Caringbah, New South Wales, Australia Centre for Pharmaceutical Innovation and Development, University of South Australia, Adelaide, South Australia, Australia. Equine Veterinary Journal ISSN DOI: /evj *Correspondence b.sykes@uq.edu.au; Received: ; Accepted: Summary Background: Pilot investigations have suggested that a novel, long-acting, injectable i.m. formulation of omeprazole (LA-OMEP) can induce acid suppression for up to 7 days following a single injection. Objectives: To investigate the pharmacodynamics and assess the clinical efficacy of the LA-OMEP formulation. Study design: Part A comprised a pharmacodynamic study. Part B consisted of a pilot clinical trial. Methods: Part A enrolled six adult Thoroughbred horses with percutaneous gastrotomy tubes. Intragastric ph was measured for continuous 23-h periods (8. 7. h) for eight consecutive days (days 7). A single 2.-g dose of a 1 mg/ml LA-OMEP formulation was administered at 8. h on day 1. In Part B, 26 horses with squamous or glandular gastric disease were enrolled based on routine gastroscopic evaluation. Once enrolled, horses received 2. g of the 1 mg/ml LA-OMEP formulation by i.m. injection on days and 7. Repeat gastroscopy was performed on days 14 (23 horses) or 16 (one horse). Results: In Part A, the percentage of time during which ph was above 4 exceeded 66% for days 1 4 in all horses and days 1 7 in four of the six horses studied. In Part B, healing was observed in all 22 (1%, 95% confidence interval [CI] 89 1%) horses with squamous disease and in nine of 12 (75%, 95% CI 47 92%) horses with glandular disease. Improvement, by at least one grade, was observed in all 22 (1%, 95% CI 89 1%) horses with squamous disease and in all 12 (1%, 95% CI 81 1%) horses with glandular disease. No worsening of lesions was observed. Lesion grade decreased over time in both the squamous (P<.1) and glandular (P =.24) mucosa. Main limitations: Small sample sizes. Conclusions: The results of the present study compare favourably with previous reports on the pharmacodynamics of omeprazole and the clinical outcomes of trials reporting response to oral omeprazole therapy. Keywords: horse; proton pump inhibitor; squamous; glandular; gastric; lesion Introduction Recent publications have pointed out that the umbrella term equine gastric ulcer syndrome (EGUS) covers numerous disease entities, of which equine squamous gastric disease (ESGD) and equine glandular gastric disease (EGGD) represent the most common conditions in the adult horse [1]. The pathogenesis of ESGD closely mirrors that of gastroesophageal reflux disease (GERD) in man in that increased exposure of the squamous mucosa to gastric acidity results in the formation of lesions [1]. The pathogenesis of EGGD is unknown, but regardless of its cause, acidsuppressive therapy is considered a cornerstone of treatment [1]. Recent studies have demonstrated that the response to omeprazole monotherapy in EGGD is markedly inferior to that in ESGD [2 4]. Specifically, only 25% of EGGD lesions healed with days of omeprazole therapy administered at 4. mg/kg bwt by mouth once per day, whereas an ESGD healing rate of 78% was achieved in the same series of studies [2 4]. Further, it appears that the response of EGGD to combination therapy with omeprazole and sucralfate is also poor to fair, with healing rates over a day treatment period reported to be between 22% [5] and 67.5% [6]. The intra-day duration of acid suppression is an important predictor of healing in human subjects. Good healing rates in GERD are achieved when the intra-day percentage of time for which ph exceeds 4 (%tph>4) is greater than 66%. Similarly, the intra-day percentage of time for which ph exceeds 3 (%tph>3) is used as a benchmark for glandular healing and requires a %tph>3 of greater than 66% [7]. It has recently been reported that following the administration of a commercial buffered paste formulation of omeprazole at the registered treatment dose of 4 mg/kg bwt by mouth once per day, the %tph>4 within the ventral stomach on day 5 may be as little as 3 4% in horses consuming high roughage diets [8]. This is below the threshold for healing reported in human subjects [7]. The use of i.v. omeprazole in horses has been described previously [9]. Administration of.5 mg/kg bwt omeprazole i.v. once per day for 5 days resulted in marked and prolonged suppression of acid production, with a mean ph of 5.27 reported approximately 24 h after the fourth dose [9]. A corresponding improvement in ESGD lesion grades was observed over the 5-day treatment period [9]. However, omeprazole is unstable once reconstituted and must be administered within 15 min, and its highly alkaline nature is potentially irritant [1], which reduces its clinical usefulness. Further, the need for daily administration by injection is likely to be impractical in many clinical settings. A novel, long-acting, injectable i.m. formulation of omeprazole (LA-OMEP) has recently been developed and administration of a single 2.-g dose has resulted in intragastric ph exceeding 4 for up to 7 days in pilot pharmacodynamic trials (B.W. Sykes, P.C. Mills; unpublished data 215). Preliminary investigations suggest that the LA-OMEP formulation is nonirritant following i.m. injection and stable at room temperature for extended durations. The availability of a safe and effective treatment for EGUS that can be administered once per week would have significant potential to improve treatment compliance and hence the availability of treatment to horses in which once per day administration of oral omeprazole is not feasible. Further, it has recently been demonstrated that ad libitum hay diets, which are commonly recommended in the management of EGUS [1], reduce the bioavailability [11], and impair the ability to raise intragastric ph [8], of oral omeprazole. Systemic administration, via the i.m. route, would reasonably be expected to bypass Equine Veterinary Journal 49 (217) EVJ Ltd 795

2 Novel intramuscular formulation of omeprazole B. W. Sykes et al. these effects if the medication was well absorbed at the injection site. If such an effect were present, the use of an i.m. formulation would potentially allow effective acid suppression to be achieved without dietary modification to accommodate for absorption, as is currently required for oral formulations of omeprazole. The objectives of the current study were: 1) to further investigate the duration of intra-day acid suppression achieved over a 7-day period following the injection of a novel, long-acting i.m. formulation of omeprazole using a recently described gastric cannulation model [12], and 2) to investigate the clinical efficacy and safety of two consecutive, once per week administrations of LA-OMEP in patients with naturally occurring ESGD and EGGD assessed over a 14-day period. The investigations were based on the hypotheses that the formulation studied would be well toleratedandthatitwouldinducemarkedandprolongedacidsuppression over the 7-day measurement period in Part A of the study, and that this would translate into good healing rates in both ESGD and EGGD in the clinical setting in Part B of the study. Materials and methods The study was conducted in two parts. Part A consisted of a pharmacodynamic study conducted in a research setting. Part B consisted of a pilot trial performed under clinical conditions in animals with naturally occurring disease. Part A Horses: Six (three male, three female) healthy Thoroughbred horses (age range: 8 15 years; body weight: 52 6 kg) were used. Horses were housed in 16-m 2 stables and bedded on wood shavings throughout the study. Horses were fed a rye grass/lucerne/oaten hay mix ad libitum. Outside the study period this was supplemented with a commercial feed pellet as required to maintain body condition, but no supplemental feeding was given during the period of intragastric ph measurement. Each horse was instrumented with a percutaneous endoscopic gastrotomy (PEG) tube as previously described [12]. Gastroscopy confirmed the location of the PEG tube to be within the ventral glandular fundus approximately 1 15 cm below the margo plicatus adjacent to the lesser curvature in each horse (Fig 1). Group allocation: Horses were assigned to treatment pairs; one pair of horses was studied each week. A single diet consisting of ad libitum access to a rye grass/lucerne/oaten hay mix that was available at all times Nylon washer PEG tube First measurement point Second measurement point Fig 1: A gastroscopic image showing final placement of the ph probe with two measurement locations 5 cm apart. The first measurement location is located approximately 1 2 mm from the surface of the mucosa. The second measurement location sits freely within the ingesta/fluid contents of the ventral stomach. PEG, percutaneous endoscopic gastrotomy. throughout the day and night was evaluated. Water was available ad libitum. Administration of medication: A single 2.-g (2-mL) dose of a 1 mg/ ml, novel, i.m. omeprazole formulation a was administered at 8. h on day 1. The major constituents of the novel i.m. formulation included omeprazole, a vehicle and a stabiliser. The major challenge imposed by the poor stability of omeprazole in liquid form was overcome by using a novel combination of excipients. The formulation was optimised for sustained release and site of injection innocuity following i.m. administration. The dose chosen was based on pilot data (B.W. Sykes, P.C. Mills; unpublished data 215). Intragastric ph measurement: The intragastric ph of each horse was monitored for a period of eight consecutive days. To achieve this, a ph probe was attached to a continuous data logger (Zephr ph b )andcalibrated prior to placement each day as per the manufacturer s instructions. The probe was then inserted for a previously determined distance and secured as previously described [12]. Data were recorded at two locations: measurement location 1 was located approximately 1 2 mm from the glandular mucosa, and measurement location 2 was located 5 cm further within the stomach (Fig 1). Data recording commenced at 8. h and continued until 7. h the following day (23 h). Mean intra-day, median intra-day, minimum and maximum ph and %t>ph4 values were reported directly from the data logger s software program. The %t>ph4 was calculated using the following equation: % time above a ph = 1% % time below a ph of 4. Baseline data were recorded on day. Daily intragastric ph following administration of the medication at 8. h on day 1 was recorded on days 1 7. Data analysis: The data were tested for normality using D Agostino Pearson omnibus K 2 normality tests. The data were non-gaussian and hence data were log-transformed prior to analysis. The %tph>4 andmedian intragastric ph for days 1 7 werecomparedwiththosefordayusinga repeated-measures analysis of variance (ANOVA) with Dunnett s multiple comparisons. Significance was set at a P<.5. Data are reported as geometric means and corresponding 95% confidence intervals (CIs). Data were analysed using GraphPad Prism Version 7 c. Part B Recruitment and examination: Thoroughbred horses from a single stable were examined as part of routine, periodic gastroscopic evaluations performed between April and November 216. Horses were selected for gastroscopy at the trainer s discretion. Prior to examination, all horses were fed their normal evening feed, but any remaining food was removed 6 8 h prior to gastroscopy. Water was not withheld and horses were exercised normally on the morning of the examination at the trainer s discretion. The horses weights were estimated using a weight tape. Horses were sedated with detomidine (Dozadine d ;1 2 lg/kg bwt i.v.) and examined using a 3.3-m flexible gastroscope e by a single investigator (BWS). The squamous mucosa was visually assessed and scored using a 4-point scale as recommended by the European College of Equine Internal Medicine (ECEIM) consensus statement [1]. The appearance of the glandular mucosa was described as recently recommended [1], and the glandular mucosa was graded using a novel system as follows: grade /2 indicates a normal mucosal surface with no evidence of loss of mucosal integrity; grade 1/2 indicates the presence of mild to moderate lesion(s) with evidence of loss of mucosal integrity, and grade 2/2 indicates the presence of severe lesion (s) with evidence of loss of mucosal integrity. Mild hyperaemia of the glandular mucosa without visible loss of mucosal integrity was not considered to be clinically significant. Based on the results of the gastroscopic examination, horses that met the inclusion criteria were enrolled in the study. Inclusion criteria for the study required horses to demonstrate grade 2/4 squamous or grade 1/ 2 glandular disease, or a combination of both, to be in race training and expected to remain in training for the next 2 weeks, to not have received any medical treatment for EGUS in the preceding 4 weeks, to be considered otherwise free of other significant disease, and to be treated 796 Equine Veterinary Journal 49 (217) EVJ Ltd

3 B. W. Sykes et al. Novel intramuscular formulation of omeprazole at predetermined times while adhering to local racing rules. Throughout the study horses were fed and exercised at the trainer s discretion. All horses received a diet typical of an Australian Thoroughbred racehorse [13]. Administration of medication: Once enrolled, horses received 2. g (2 ml) of the 1 mg/ml LA-OMEP formulation by i.m. injection on days and 7. All medications were administered by the principle investigator (BWS). Alternate sides of the neck were used for the two injections, and the injection site was monitored for adverse effects twice per day by the trainer. Follow-up gastroscopy: Repeat gastroscopy, as described above, was scheduled on day 14. Lesion healing was defined as a change to grade. Horses were considered to have improved if the lesion grade for the region decreased by at least one grade. Horses with a sub-maximal starting lesion grade were considered to have worsened if the grading of that particular mucosa increased by at least one grade. Data analysis: Healing and improvement rates, and corresponding 95% CIs, are reported. Jeffrey s 95% CIs were calculated using online statistical software f. Pre- and post-treatment lesion grades are presented as the median, interquartile range (IQR) and range. A two-tailed Wilcoxon signedrank test was used to assess changes in ulcer grades within groups over time using an online calculator g. Significance was set at a P<.5. Results Part A All horses successfully completed the study. A single horse developed mild swelling at the injection site h post-administration. The swelling was non-painful and resolved within 3 days without specific therapy. No other adverse events were noted. The majority of the data were normally distributed. A complete dataset was available for analysis. Figures 2 and 3 show the mean %tph>4 andthemeanofthemedian intra-day ph values, respectively, with 95% CIs, over the 8-day period. The % tph>4 was higher than on day on days 1 7 in both measurement locations 1 (P<.1) and 2 (P<.3). In measurement location 1, the median intra-day ph was higher than on day on days 1 7 (P<.4). In measurement location 2, the median intra-day ph was higher than on day ondays1 5 (P<.3). Part B Horses: A total of 38 horses were examined prior to enrolment in the study; 26 horses (age range: 2 7 years) were found to meet the inclusion criteria. Two horses were lost from follow-up (one as a result of a severe suspensory ligament injury and the other as a result of severe exerciseinduced pulmonary haemorrhage) and were excluded from data analysis. The final study population consisted of 14 geldings and 1 mares with estimated weights ranging from 45 to 59 kg. Treatment with a total body dose of 2. g of the LA-OMEP formulation resulted in an approximate dose range of mg/kg bwt. The horses had been in work for between 6 weeks and >12 months. Two horses received additional treatment during the study period; Horse 5 received treatment with phenylbutazone (4.4 mg/kg bwt by mouth once per day) and trimethoprim/sulphadimidine (3 mg/kg bwt by mouth twice per day) throughout the study period for management of a hindlimb cellulitis. Horse 24 was treated for ongoing orthopaedic issues with intraarticular triamcinolone and hyaluronic acid (total triamcinolone dose: 4 mg) on day 8. Horse 5 was rested for the treatment duration and Horse 24 was rested from fast work on days 9 11 inclusive. All other horses remained in full race training during the study period. No injection site reactions were observed. Gastroscopy: The entire squamous mucosa was adequately observed in all examinations. Residual fluid in the stomach obscured observation of the most ventral portion of the glandular body; however, the majority of the glandular body and entire pyloric antrum were visible in all horses. Followup gastroscopy was performed on day 14 in 23 horses and, owing to its racing schedule, on day 16 in one horse (Horse 11). Lesions of the squamous and glandular mucosa were present in 22 and 12 of the 24 horses, respectively, at enrolment. Healing was observed in all 22 (1%, 95% CI 89 1%) horses with squamous disease and in nine of the 12 (75%, 95% CI 47 92%) horses with glandular disease. Improvement, by at least one grade, was observed in all 22 (1%, 95% CI 89 1%) horses with squamous disease and in all 12 (1%, 95% CI 81 1%) horses with glandular disease. Worsening of ESGD or EGGD lesions was not observed. Pre- and post-treatment lesion grades and descriptive terminology for the glandular mucosa for each horse are shown in Table 1. Pre- and posttreatment lesion grades for horses with a squamous lesion grade of 2/4 (n = 22)oraglandularlesiongradeof 1/2 (n = 12) at enrolment are displayed in Fig 4. Lesion grade decreased over time for both the squamous (P<.1) and glandular (P =.2) mucosa. Discussion The magnitude and duration of acid suppression achieved with the LA- OMEP formulation, as documented by Part A of the present study, exceeds those previously reported for oral omeprazole under similar dietary conditions [8,14]. In an earlier report using a similar model, and studying horses consuming ad libitum roughage supplemented with a grain meal twice per day, a commercial buffered paste formulation of omeprazole achieved a ph>4 for only 14 h and 11 h on days 2 and 7 of treatment, respectively, even at the registered treatment dose of 4 mg/kg bwt by mouth once per day [14]. Similarly, a recent report evaluating the effectiveness of the same commercial paste, and similarly using a dose of 4 mg/kg bwt by mouth once per day in horses consuming ad libitum %tph> Measurement location 1 Measurement location Fig 2: The effect of a single 2.-g (2-mL) dose of a 1 mg/ml, novel, injectable omeprazole formulation administered at 8. h on day 1 following a baseline measurement on day, on mean intra-day percentage of time for which ph exceeds 4 (%tph>4) at two measurement locations in six horses on an ad libitum hay-only diet. Data are reported as individual data points and geometric means with corresponding 95% confidence intervals. The %tph>4 was higher than on day on days 1 7 in both measurement locations 1 (P<.1) and 2 (P<.25). Equine Veterinary Journal 49 (217) EVJ Ltd 797

4 Novel intramuscular formulation of omeprazole B. W. Sykes et al. 12 Measurement location 1 Measurement location 2 1 Median intra-day ph Fig 3: The effect of a single 2.-g (2-mL) dose of a 1 mg/ml, novel, injectable omeprazole formulation administered at 8. h on day 1 following a baseline measurement on day, on the mean of the median intra-day ph values at two measurement locations in six horses on an ad libitum hay-only diet. Data are reported as individual data points and geometric means with corresponding 95% confidence intervals. In measurement location 1, median intra-day ph was higher than on day on days 1 7 (P<.4). In measurement location 2, median intra-day ph was higher than on day on days 1 5 (P<.34). TABLE 1: Pre- and post-treatment lesion grades and descriptive terminology for the glandular mucosa for each horse Horse Grade Glandular pre-treatment Grade Glandular post-treatment Mild hyperaemia with smooth mucosa 4 Mild hyperaemia with smooth mucosa Mild hyperaemia with smooth mucosa 1 Mild hyperaemia with smooth mucosa 11 Mild hyperaemia with smooth mucosa 12 Slight hyperaemia with smooth mucosa 13 1 Single, moderately severe, ventral, linear lesion within pyloric antrum 14 1 Three small, moderately severe, focal lesions within pyloric antrum 15 1 Moderately severe, linear lesions with roughened epithelium throughout pyloric antrum radiating out from pylorus 16 1 Single, moderately severe, ventral, linear lesion within pyloric antrum 17 1 Moderate hyperaemia with roughened mucosa Slight hyperaemia with smooth mucosa 18 1 Two moderately severe, ventral, linear lesions within pyloric antrum 19 1 Single, moderately severe, ventral, linear lesion within pyloric antrum 2 1 Single, moderately severe, ventral, linear lesion within pyloric antrum 21 2 Single, large (approx cm), severe, ventral linear lesion within pyloric antrum 1 Unchanged in size but less severe with granulated appearance 22 2 Moderately severe, linear lesions with roughened epithelium throughout pyloric antrum radiating out from pylorus plus three deep, focal lesions 1 Single ventral linear lesion with granulated appearance remaining 23 1 Moderately severe, linear lesions with roughened epithelium throughout pyloric antrum radiating out from pylorus 24 2 Moderately severe, linear lesions with roughened epithelium throughout pyloric antrum radiating out from pylorus plus three deep, focal lesions Follow-up gastroscopy was performed on day 14 in 23 horses and on day 16 in Horse Two superficial, ventral, linear lesions within pyloric antrum roughage, reported %tph>4 values on day 5 of approximately 4% and 3% for measurement locations 1 and 2, respectively [8]. In human subjects, good healing rates in GERD, which is analogous to ESGD, are achieved when the %tph>4 exceeds 66% [7]. This benchmark was exceeded, using measurement location 1 as the reference point, for days 1 4 in all animals and for all 7 days of the monitoring period in four of six animals. The magnitude and duration of suppression observed at measurement location 1 in Part A of the study appeared to transfer into Part B of the study, in which 1% of patients demonstrated complete ESGD healing over the 14-day period. This compares favourably with reported ESGD healing response rates following oral omeprazole administration that range from 73% to 87% with days of treatment [2,3,15 18]. It suggests that greater durations of intra-day acid suppression may result in more rapid healing in the horse as they do in human subjects in whom the GERD healing rate has been shown to be directly related to the duration of intra-day acid suppression [7]. The %tph>3 is used as a benchmark for glandular healing and a %tph>3 of greater than 66% is required in man for the healing of glandular disease [7]. Unfortunately, limitations in the software of the reporting program prevented the determination of %tph>3 in the present study. Regardless, it 798 Equine Veterinary Journal 49 (217) EVJ Ltd

5 B. W. Sykes et al. Novel intramuscular formulation of omeprazole 4. P<.1 P = Squamous lesion (pre-treatment) Squamous lesion (post-treatment). Glandular lesion (pre-treatment) Glandular lesion (post-treatment) Fig 4: Pre- and post-treatment lesion grades in horses with a squamous lesion grade of 2/4 (n = 22) or a glandular lesion grade of 1/2 (n = 12) at enrolment. Once enrolled, horses received 2. g (2 ml) of the 1-mg/mL formulation of omeprazole by i.m. injection on days and 7. Repeat gastroscopy was performed at day 14 (23 horses) or day 16 (one horse). has been proposed that %tph>4 may be a more conservative benchmark until species-specific breakpoints for healing are determined [8]. The rate of EGGD healing in the present study compared favourably with rates in previous reports as 75% of EGGD lesions healed within the treatment period, whereas only 25% of EGGD lesions healed with days of oral omeprazole therapy at 4. mg/kg bwt administered once per day in one series of studies [2 4]. Further, improvement was seen in 1% of animals in the present study compared with 34% of animals in a previous study [2]. No worsening was observed in the present study, by contrast with a previous report in which 36% of animals were reported to have worsened in the face of oral omeprazole therapy [2]. Acid suppression was not maintained in all horses for the full 7-day study period in Part A of the study. However, the duration of acid suppression over the 7-day treatment period compares favourably with the reported requirements for intra-day %tph>4 on a 24-h dosing interval. As such, complete acid suppression may not be required for the full 7-day period for healing to occur, as long as the %tph>4 within the inter-treatment interval, in this case 7 days, is adequate. This statement is supported by an analysis of the magnitude and duration of acid suppression observed in Part A of the study and the clinical results obtained in Part B. Considering the findings overall, the present authors propose that the benchmarks reported in other species are likely to represent a fair approximation of the acid suppression required for healing to occur in the horse. The reason, or reasons, for the variation in individual acid suppression response are not known. It has been previously reported that oral bioavailability of omeprazole in horses may vary by up to 1-fold [19]. In human subjects, variation in the efficacy of omeprazole has been reported and is primarily related to mutations in the CYP2C19 gene and changes in the rate of elimination [2]. These factors have not been investigated in the horse. Whether the inter-individual variation observed relates to variations in absorption of the drug from the i.m. injection site over time, or variations in the rate of elimination, warrants further investigation. As in a previous report [8], differences were observed between the two measurement locations of intragastric ph, although the measurement locations were only 5 cm apart. A similar effect has been reported in human subjects when intragastric ph is measured in multiple locations [21,22]. It is unclear which measurement location more accurately reflects healing conditions at the level of the mucosa, but it has been proposed previously [23] that measurement location 1 may be more predictive as it is fixed in a known position 1 2 mm from the glandular mucosa, and the level of acid suppression reported at measurement location 1 in a previous study evaluating omeprazole [8] correlates well with reported healing rates in clinical trials for the doses studied. By contrast, the exact location of the tip of the probe, and thus of measurement location 2, is not known but it can reasonably be expected to be buried in the ingesta [23]. The glandular grading system used in the present study has not been previously reported and it has been suggested that the use of hierarchical grading systems for the glandular mucosa be avoided as they imply linearity to disease [1]. The data for each horse presented in Table 1 include descriptive terminology to partly address this.however, the current authors believe that the use of a simplified grading system such as that used in Part B of the present study may be useful for distinguishing partial responses to therapy, such as where the overall appearance of an EGGD lesion has improved but mucosal reconstitution is not yet evident. Further, the authors acknowledge that the definition of clinically significant in this study as defined by the apparent loss of mucosal integrity has yet to be validated in the horse, and that it has been proposed that in human subjects hyperaemia of the glandular mucosa may be adequate for pain to be present [24]. However, the current group proposes that the obvious loss of mucosal integrity is relatively easy to assess gastroscopically and that it is widely used as a clinical intervention point. Further studies investigating the use and validity of grading systems, and the clinical relevance of hyperaemia would be greatly beneficial. Minimal side effects were observed. A single animal developed mild, self-resolving swelling following injection, but no other adverse effects were noted. The potential effects of long-term omeprazole administration in the horse have not been studied. A single study evaluating the effects of short-term oral omeprazole administration found no deleterious effects on bone density or serum calcium concentrations over a 6-day period [25]. Whether longer duration of therapy or repeated i.m. administration are potentially associated with an increased risk for complications, above that observed in the present study, warrants consideration. Further, the pharmacokinetic and elimination profile of the LA-OMEP formulation has not been reported. Consideration should be given in this regard in jurisdictions that prohibit competing on omeprazole. Several weaknesses were present in the current study. Firstly, the horses were stabled and not exercised in Part A. It is not known whether higher magnitudes of acid suppression are required in exercising horses. Equine Veterinary Journal 49 (217) EVJ Ltd 799

6 Novel intramuscular formulation of omeprazole B. W. Sykes et al. However, the magnitude and duration of acid suppression observed in resting horses in Part A of the study appear to correlate well with the clinical healing observed in Part B. Secondly, the dietary conditions in Part A differed from those in Part B. The ad libitum roughage diet chosen in Part A of the study was selected in order to represent the most rigorous model for testing the efficacy of omeprazole. It has been suggested that acid production may be higher in ad libitum roughage diets as the magnitude of gastrin production elicited by the feeding of a hay meal has been shown to be greater, and the speed of onset of gastrin production faster, than when a grain meal is fed [26]. This suggests that gastric distension may play a role in the dynamics of gastrin release and the magnitude of acid production [26], and that higher doses of proton pump inhibitors may be required in ad libitum roughage diets. Further, the use of an ad libitum roughage diet allows comparison with previous studies [8,14] in which the efficacy of oral omeprazole under such conditions has been below therapeutic thresholds reported in humans. The animals and the diet in Part B of the study were selected primarily for the ability to conveniently sample animals in a population with previously reported high prevalences of both ESGD and EGGD [2 4,27]. Further studies in populations consuming ad libitum roughage diets are needed to confirm whether the high response rates in ESGD and EGGD observed in Part B of the present study can be replicated in such populations. Thirdly, a total-body dose was chosen over a mg/kg bwt dose primarily for the purposes of convenience and ease of dosing. However, inter-individual variability in factors such as local absorption and metabolism may be more likely to affect efficacy in a relatively homogeneous population, such as that chosen, than minor variations in the mg/kg bwt dose. Further evaluation of the relative benefits of a total-body dose vs. a mg/kg bwt dosing strategy warrants consideration, especially if the bodyweight range of animals being treated varies beyond that studied in the present study. Fourthly, the study was unblinded. This creates a potential bias as the investigator responsible for the examinations may have been inadvertently influenced by prior knowledge of previous lesion grade and the treatment given. Fifthly, no control group was included. However, the response to oral omeprazole therapy of the population used in Part B of the present work has been studied previously under almost identical management conditions [2 4,28]. Nevertheless, although indirect comparisons, as drawn in this study, are valid, the present authors acknowledge that direct studies comparing the LA-OMEP formulation with oral omeprazole would be ideal. Finally, the number of animals studied was small, as evidenced by the wide 95% CI for EGGD healing rates. However, the results of this preliminary study are promising and further blinded studies in larger populations comparing the formulation described with the current therapeutic standard of oral omeprazole appear warranted. Conclusions The results of Part A of the present study compare favourably with the findings of previous reports on the pharmacodynamics of oral omeprazole. Specifically, the acid-suppressive effect observed following the administration of the LA-OMEP formulation was more consistent and predictable than that observed when oral omeprazole is administered, especially in the presence of ad libitum hay. Similarly, the clinical outcomes reported in Part B of the present study compare favourably with those in previous studies reporting the healing and improvement rates of ESGD and EGGD achieved with oral omeprazole therapy. Specifically, the healing observed with the LA-OMEP formulation was both more complete and more rapid than that described in previous reports of the use of oral omeprazole. Minimal side effects were observed: a single animal developed mild, self-resolving swelling following injection and no other adverse effects were noted. Further investigations into the pharmacokinetics, elimination, safety and clinical efficacy of the formulation in different populations appear warranted. Authors declaration of interests B.W. Sykes is engaged as a consultant to Luoda Pharma Pty Ltd. S.W. Page is a director and shareholder of Luoda Pharma Pty Ltd. Ethical animal research The study was performed under ethics permits from the New South Wales Department of Primary Industries (TRIM 15/1795[9] and TRIM 1/ 178[1]). Source of funding This study was funded by Luoda Pharma Pty Ltd. Acknowledgements The authors acknowledge Portoscope.com, Inc. for the generous loan of a gastroscope for research purposes and also thank Katja Sykes, Danny Edwards and Brett Bellamy, Coffs Harbour, NSW, Australia, for their assistance with the studies. Authorship B.W. Sykes contributed to the study design, execution and data analysis. S.W.Page,K.Kathawala,Y.SongandS.Gargcontributedtoformulation development. C. Underwood contributed to the statistical analysis. P.C. Mills contributed to the study design. All authors contributed to the preparation of the paper and approved the final version of the manuscript. Manufacturers addresses a Luoda Pharma Pty Ltd, Caringbah, New South Wales, Australia. b Sandhill Scientific, Inc., Highlands Ranch, Colorado, USA. c GraphPad Software, Inc., La Jolla, California, USA. d Axon Animal Health, Belrose, New South Wales, Australia. e Portascope.com, Inc., Bradenton, Florida, USA. f Ausvet Pty Ltd, URL g VassarStats, URL References 1. 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