Methods

The enrollment criteria for this study included dogs that had been consistently treated with PPIs over 6 months. For the purpose of this study, “long term” was defined as 6 months or longer, in line with definitions found in human literature.²⁴ Electronic medical records between March 2004 and March 2023 were retrospectively reviewed to identify dogs that met the enrollment criteria at the Veterinary Teaching Animal Hospital of Chungnam National University. Upon reviewing the medical records, iMg readings have been available since 2019 at this institution. Subsequently, dogs that meet the inclusion criteria and had iMg readings from 2019 were included. The following data were retrieved from each dog’s medical record: signalment, physical examination, medical history, types, dosages, frequency, duration, and confirmation of continuous prescription of PPIs, concurrent medications, CBC, serum biochemistry profile, and venous blood gas.

All whole-blood iMg levels from the dogs were recorded, including measurements obtained from routine follow-ups for long-term management of the dogs’ primary diseases and those obtained when the dogs presented with illness. The iMg levels obtained during IV fluid therapy were excluded. The iMg level at the initiation of PPI treatment was designated as the iMg at presentation. The nadir iMg was defined as the lowest iMg value recorded after 6 months of PPI. The endpoint iMg was defined as the iMg value recorded at the final time point of the monitoring period. If only 1 iMg value was measured after 6 months, that value was used as both the nadir iMg and the endpoint iMg.

The reference interval (RI) for iMg, as determined by the analyzer used during the study period (Stat Profile pHOx Ultra; NOVA Biomedical), was established to document the incidence of hypomagnesemia in the study group. Therefore, client-owned healthy dogs were prospectively recruited to determine the RI of iMg according to the guidelines published by the American Society for Veterinary Clinical Pathology (Quality Assurance and Laboratory Standards).²⁵ The blood sample collection for the RI study was approved by the Chungnam National University IACUC (reference number 202310A-CNU-192). Informed consent was obtained from the owners of the healthy control dogs. Dogs were considered healthy if their clinical history and physical examinations were unremarkable and they had no clinically relevant abnormalities on CBC (Procyte One, IDEXX) and serum chemistry panel (Catalyst Chemistry Analyzer; IDEXX). Dogs were excluded if they were on medications other than preventative medications or had a history of medical illness. Each blood sample was collected via direct venipuncture or immediately after IV catheterization to measure venous blood gas. The whole-blood sample was immediately transferred, placed in lithium heparin tubes, and analyzed using the Stat Profile pHOx Ultra (NOVA Biomedical), which utilizes ion-selective electrode methods. The laboratory personnel who operated the analyzer had received prior training and followed the manufacturer’s guidelines. De novo RI were calculated using Reference Value Advisor (version 2.1).²⁶ The sample size was large enough to compute the nonparametric RI, and a 90% CI was determined using a bootstrap method.

In addition to assessing the incidence of hypomagnesemia based on the RI, iMg levels in the study group were compared to those in a control group of 20 dogs, selected from the 62 healthy dogs used for the de novo RI establishment. The 20 dogs were matched to the long-term PPI group based on age, sex, and body weight. Ionized magnesium levels at presentation, at the nadir, and at the endpoint in the study group were compared with those in the control group. Finally, iMg levels at presentation were compared to endpoint levels to investigate the impact of long-term PPI use.

Results

Over the course of the 20-year study period, a total of 821 dogs prescribed PPIs were identified. Of the 821 dogs, 811 were excluded from the study due to receiving PPIs for less than 6 months, not being on PPIs consistently, or having incomplete medical records. Among these, 10 dogs had received PPIs continuously for 6 months or longer, had available iMg recordings, and were enrolled to the study. All PPIs administered for over 6 months were exclusively esomeprazole (AstraZeneca AB). This study group included 1 female, 2 spayed females, and 7 neutered males. The median (range) of age and body weight of the included dogs was 9 years (5 to 10) and 4.25 kg (2 to 45), respectively. The most common breeds were Pomeranian (n = 3), Maltese (n = 2), and 1 each of Labrador Retriever, Beagle, mixed breed, Chihuahua, and Cavalier King Charles Spaniel. The primary diseases of the dogs in study group consist of caudal occipital malformation syndrome (n = 3), hydrocephalus (n = 3), CKD (n = 1), transitional cell carcinoma (n = 1), melanoma (n = 1), and chronic gastritis (n = 1). The indications for esomeprazole administration were to decrease CSF reduction (n = 6) and gastrointestinal ulcer management or prevention (n = 4). There were comorbid diseases in 4 dogs (Table 1). The median duration of esomeprazole was 28 months (6 to 94 months). The prescribed dosages of esomeprazole ranged from 0.5 to 5 mg/kg every 12 to 24 hours. Most dogs (7/10 [70%]) received either 0.5 mg/kg or 1 mg/kg twice daily. The frequency of iMg measurements varied among the dogs, with a median (range) of 11 (3 to 18) measurements per dog.

The level of iMg in dogs with long-term esomeprazole is presented in Table 1. After 6 months of esomeprazole treatment, the median of the nadir iMg levels measured was 0.96 mg/dL (0.87 to 1.41), and the median of the endpoint iMg was 1.03 mg/dL (0.87 to 1.41). The comparison of iMg levels between dogs at presentation (1.19 mg/dL, 0.97 to 1.22) and at the endpoint iMg (1.09 mg/dL, 0.87 to 1.41) was available in 5 dogs, with no significant differences observed between these measurements (P = .546).

A total of 62 healthy adult dogs were recruited to identify the RI for iMg. The median age of these dogs was 3 years, ranging from 1 year to 12 years. There were 22 (35.5%) males, 17 (27.4%) neutered males, 10 (16.1%) females, and 13 (21%) neutered females. The most common breeds were Beagle (n = 29), Golden retriever (n = 5), Bichon Frise (n = 4), Maltese (n = 3), mixed-breed dog (n = 3), Pomeranian (n = 3), Miniature Poodle (n = 3), Welsh Corgi (n = 2), Border Collie (n = 2), and 1 each of Chihuahua, Doberman pinscher, German Shepherd, Labrador Retriever, Pug, Shih Tzu, and Siberian Laika. The RI for iMg was determined as 0.73 to 1.43 mg/dL (0.30 to 0.59 mmol/L). A single outlier was detected using the Tukey method but was retained as there was no known aberrancy with this sample. The 90% CIs for the lower limit (0.73 mg/dL) and upper limit (1.43 mg/dL) were 0.58 to 0.87 mg/dL and 1.33 to 1.46 mg/dL, respectively. Based on the de novo RI, ionized hypomagnesemia and hypermagnesemia in this study were defined as iMg below 0.73 mg/dL and above 1.43 mg/dL, respectively. None of the dogs in the study group developed either hypomagnesemia or hypermagnesemia based on the RI.

The median (range) age of these 20 healthy control dogs was 7 years (5 to 12 years), and the median body weight was 7.95 kg (2 to 38 kg). There were no significant differences between the long-term PPI group and the matched control group in terms of sex (P = .818), age (P = .059), or weight (P = .278). The median (range) iMg level of the control group was 1.17 mg/dL (0.83 to 1.46 mg/dL). While the nadir iMg observed 6 months after long-term esomeprazole treatment was significantly lower (P = .031) compared to the control group (Figure 1), no significant differences were found between the endpoint iMg compared to the healthy controls (P = .179).

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Box-and-whisker plots comparing ionized magnesium (iMg) concentrations between long-term esomeprazole-treated dogs and healthy control dogs. A significant reduction in iMg concentrations was observed at the lowest point after 6 months of esomeprazole treatment (median, 0.96 mg/dL; range, 0.87 to 1.41) compared to healthy control dogs (median, 1.17 mg/dL; range, 0.83 to 1.46) (P = .031). However, no significant differences were found in iMg concentrations at the treatment endpoint (median, 1.03 mg/dL; range, 0.87 to 1.41) when compared to the healthy control dogs (P = .179).

Citation: American Journal of Veterinary Research 85, 12; 10.2460/ajvr.24.05.0157

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All dogs receiving esomeprazole were concurrently on other medications, which varied widely and had their dosages adjusted throughout the study period. The most commonly coadministered medications included acetazolamide in 4 dogs (40%), maropitant in 3 dogs (30%), and furosemide and piroxicam in 2 dogs each (20%). Additional medications, such as zonisamide, silymarin, pimobendan, amoxicillin-clavulanate, carboplatin, metronidazole, diazepam, ursodeoxycholic acid, gabapentin, toceranib phosphate, pregabalin, phenoxybenzamine, and bethanechol, were also prescribed but were not categorized under specific drug classes. Among these, the list of medications that lower magnesium levels are the following: acetazolamide, furosemide, carboplatin.^20,21

Discussion

To the best of our knowledge, this retrospective study is the first to assess magnesium levels in dogs who received long-term PPIs. The 10 dogs included in the study were treated with long-term esomeprazole for periods ranging from 6 to 94 months. Based on the de novo RI determined in this study, none of the dogs developed ionized hypomagnesemia after long-term use of esomeprazole. However, the wide CI of the low and high end of the de novo reference range, as well as the narrow range of iMg variations, makes it challenging to determine the true incidence of hypomagnesemia. When the iMg of the study group was compared with those of an age-, sex-, and weight-matched control group, no significant differences were observed at presentation, nadir, or endpoint when compared to the control group. This contrasts with human studies, which have shown an association between long-term PPIs and an increased risk of developing hypomagnesemia.¹⁷

The present study is the first in veterinary medicine to evaluate the long-term use of esomeprazole in dogs admitted to the tertiary animal hospital. The current study identified only 10 dogs over the 4-year span that were consistently on esomeprazole for over 6 months, indicating a raised awareness of the proper use of PPIs in veterinary medicine over the past decade. This increased attention is largely due to emerging research on the side effects and potential risks associated with long-term PPI use as highlighted in human medicine and reflected in the American College of Veterinary Internal Medicine consensus statement on the use of PPIs in dogs and cats. Given that the dogs in the study were included over the past 4 years, several were treated for indications that would now be considered inadequate based on current standards. In the study, 4 dogs received long-term esomeprazole for potential adverse effects of drug-induced gastrointestinal toxicity and the treatment of gastrointestinal ulcers/erosions. One dog with transitional cell carcinoma received long-term esomeprazole to prevent potential gastrointestinal side effects from piroxicam toxicity in 2021. However, a recent study²⁷ has shown that omeprazole was not effective in reducing the adverse effects of piroxicam in dogs. Three other dogs received esomeprazole to treat toceranib-induced gastrointestinal toxicity, chronic gastritis, and uremic gastritis due to CKD. Esomeprazole therapy was continued even after the resolution of the gastrointestinal clinical signs, indicating potentially inappropriate use based on the American College of Veterinary Internal Medicine consensus guidelines.⁵ Further studies are needed to document the current practice patterns of PPI prescription in dogs and to determine if the practice shift has contributed benefits such as reduced pill burden and lower client costs.

The present study included the largest number of dogs (n = 62) reported so far to determine the RI for iMg, which ranged from 0.73 to 1.43 mg/dL (0.3 to 0.58 mmol/L). One study²⁸ involving 61 healthy dogs established an RI of 1.05 to 1.37 mg/dL using the NOVA CRT 8 electrolyte analyzer (Nova Biomedical). Another study²⁹ with 22 healthy dogs reported an RI of 0.61 to 0.99 mg/dL using the Stat Profile (Nova Biomedical). Additionally, a study³⁰ with 24 healthy dogs reported an RI of 1.07 to 1.22 mg/dL using the Stat profile Prime Plus VET Critical Care Analyzer (Nova Biomedical). Finally, a study³¹ with 30 healthy dogs established a range of 1.02 to 1.41 mg/dL using the NOVA CRT 8 electrolyte analyzer (Nova Biomedical). Although a sample size exceeding 120 is considered optimal for establishing de novo RIs, more than 40 samples and employing robust methodologies are considered adequate for setting a new RI for iMg.²⁵ The RI reported in the present study is slightly broader but generally similar to those reported in previous studies,^28–31 a difference that could be attributed to variations in the machines used or sample sizes, even when employing the same ion-selective electrode method. Even though this study used the largest number of dogs to develop an RI for iMG, the CIs of the lower and higher limits of the RI highlight the need for future studies with a larger number of dogs exceeding 120 that determines the RI using robust method and thus will aid in the assessment of hypo- or hypermagnesemia and its association with PPIs.

Based on the de novo RI, none of the dogs in the present study developed hypomagnesemia. However, several considerations must be taken into account when interpreting the incidence reported in this study. First, a more robust RI is needed to accurately determine the incidence of ionized hypomagnesemia given the variation in the lower limit of the RI reported in previous studies.^28–31 Compared to previously reported RIs, the de novo RI determined in this study has a slightly different range, which could influence the interpretation of magnesium levels. Secondly, it is important to note that human studies³² have shown that detecting hypomagnesemia requires a large cohort due to its low incidence in long-term studies. Those studies also eliminated other confounding factors to eliminate any variables that could impact magnesium levels to accurately assess the independent impact of PPIs to magnesium levels.^32,33 The current study, however, was limited to only 10 dogs despite extensive medical record review, making it very likely that any subtle differences in magnesium levels could not be detected in such a small sample size. When comparing the long-term PPI group to a control group, a power calculation was conducted based on the expected difference in mean iMg levels between 2 groups. With an effect size of 0.8 (large), a significance level of 0.05, a power of 0.8, and a sample size ratio of 1 between the 2 groups, 26 subjects were required per group. As this study aimed to identify potential associations, the findings should be interpreted with caution, and larger studies are needed to validate these results. Third, amongst PPIs, esomeprazole has been shown to have the lowest incidence of hypomagnesemia in long-term human studies.⁴ Lastly, human clinical studies³² have reported the incidence of hypomagnesemia based on total magnesium measurements, whereas this study focused solely on iMg based on the available analyzer in this institution. Research recommendations differ, with some human studies^34–36 suggesting the measurement of total magnesium to screen for chronic magnesium imbalances, whereas others prefer iMg as it is the biologically active form. This limits the direct comparability of these findings with human studies.

In addition to investigating the incidence of hypomagnesemia based on the de novo RI, iMg levels at the initiation of esomeprazole, the lowest after 6 months of esomeprazole, and the iMg at the end of the treatment were compared with those of a matched control group. The authors chose to investigate the iMg after 6 months based on human studies²⁴ that examined the impact of long-term PPI use on magnesium levels in patients receiving PPIs for 6 to 12 months or longer. The lowest iMg after 6 months of esomeprazole treatment was significantly lower, although there was no significant difference in iMg levels at presentation or at the study endpoint compared to healthy controls. Additionally, iMg levels at initiation of esomeprazole were not significantly different from the endpoint iMg, raising questions about the cause of the lowered nadir iMg. The authors excluded any measurements obtained during hospitalization to account for the potential impact of IV fluids or other concurrent medications on iMg levels. However, the iMg measurements taken at the presentation of each hospital visit were still included, suggesting that the lowest iMg levels could have been influenced by clinical signs when the dogs presented with vomiting, anorexia, diarrhea, or other concurrent illnesses that reduce magnesium intake or increase its loss. Esomeprazole treatment was continued during hospitalization, and the endpoint iMg levels remained within reference range and not significantly different than the iMg levels at the initiation of esomeprazole. This suggests that the lower nadir iMg was more likely due to the concurrent illness rather than the esomeprazole itself. The absence of negative side effects from long-term esomeprazole reported in this study should be interpreted with caution.

Research on the safety of the long-term use of PPIs in veterinary medicine remains scarce. One experimental study³⁷ demonstrated that administering omeprazole orally to healthy beagle dogs daily for a period of 7 years resulted in no adverse effects, including no alterations in total serum magnesium levels, in any of the subjects. One case report described the development of fundic gland polyps in a Maltese dog with prolonged omeprazole treatment.³⁸ The appropriate indication of long-term PPI use in veterinary medicine has not been established. However, in humans, long-term PPI use is recommended for conditions including erosive esophagitis, esophageal stricture resulting from gastroesophageal reflux disease, Zollinger-Ellison syndrome, eosinophilic esophagitis, gastroprotection for patients at high risk of gastrointestinal bleeding from NSAID use, and the prevention or progression of idiopathic pulmonary fibrosis.³⁹ In the present study, 10 dogs received long-term esomeprazole treatment, with the longest duration being 94 months. Although no specific adverse effects associated with esomeprazole use were documented in any of the dogs, the study did not specifically evaluate the safety of esomeprazole.

The present study aimed to document the concurrent medications known to reduce magnesium level in dogs included in the study. Human studies have reported concurrent medications that are associated with the development of hypomagnesemia. Medications can lead to magnesium deficiency, primarily through 3 mechanisms: first, drugs such as insulin promote the entry of magnesium into cells. Second, substances such as laxatives or PPIs cause gastrointestinal loss of magnesium. Third, medications that increase urinary magnesium excretion or inhibit its reabsorption, including chemotherapeutics, such as carboplatin; immunosuppressants, such as cyclosporine; loop diuretics, such as thiazide diuretics; and carbonic anhydrase inhibitors.^20,21 Several human studies^21,22 have indicated that concurrent long-term administration of PPIs and loop diuretics significantly elevates the risk of total hypomagnesemia. In this study, 5 dogs received diuretics, such as acetazolamide and furosemide, and 1 dog received carboplatin. Due to the retrospective nature of the study, the frequency, duration, and timing of these concurrent medications relative to the iMg measurements could not be documented. Despite the use of these medications, hypomagnesemia was not observed during the study period in these dogs. Further research is needed to determine whether the concurrent use of PPIs with other medications is associated with the increased risk of the development of hypomagnesemia in dogs.

The present study has several limitations. First, the sample size of cases in the long-term PPI group was small despite an extensive search through medical records spanning 20 years. This small sample size limits the robustness and generalizability of the findings. Second, although a variety of PPIs, such as pantoprazole, omeprazole, and esomeprazole, are used in veterinary medicine, esomeprazole was the only PPI consistently administered over 6 months at this institution and was subsequently included in the present study. This selection limits the ability to directly compare the effects of different PPIs on iMg. Lastly, conducting long-term studies presents marked difficulties due to the potential use of dietary supplements and the variability in dogs’ diseases, diets, and environments, which could affect the levels of iMg. This variability likely impacted the study results herein. Therefore, prospective studies in a large number of dogs with robust study design are needed to confirm these findings and effectively address potential biases.

In summary, this preliminary study did not detect ionized hypomagnesemia in the 10 dogs that received long-term esomeprazole treatment for 6 months or longer. Further prospective research involving larger cohorts and a standardized protocol, including serial measurements of iMg, is necessary to investigate the impact of long-term PPI use on magnesium levels in dogs.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.

ORCID

J. Lee https://orcid.org/0000-0003-2920-7171

S. Evans https://orcid.org/0000-0003-2182-0684

J. Her https://orcid.org/0000-0003-3150-591X