Glargine insulin for treatment of naturally occurring diabetes mellitus in dogs

Rebecka S. Hess Department of Clinical Studies-Philadelphia, Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.

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 DVM, DACVIM
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Kenneth J. Drobatz Department of Clinical Studies-Philadelphia, Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.

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 DVM, MSCE, DACVIM, DACVECC

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Abstract

Objective—To evaluate the effects of twice-daily glargine insulin administration in dogs with diabetes mellitus.

Design—Open-label, prospective clinical trial.

Animals—10 dogs with naturally occurring diabetes mellitus.

Procedures—Dogs with poorly regulated or newly diagnosed diabetes mellitus were enrolled if their owners agreed to return them to the hospital at 1- to 3-week intervals for 4 follow-up visits. During each follow-up visit, blood glucose concentrations were measured every 2 hours for at least 10 hours after feeding a diet high in insoluble fiber and after administration of glargine insulin (time 0). The initial glargine insulin dosage was 0.5 U/kg (0.23 U/lb) SC twice daily.

Results—All dogs had well-regulated diabetes mellitus at a mean ± SD of 38 ± 14 days (median, 43 days; range, 7 to 55 days) following study enrollment. At the time diabetes mellitus was well regulated, mean glargine insulin dosage was 0.5 ± 0.15 U/kg (0.23 ± 0.068 U/lb; median, 0.5 U/kg; range, 0.32 to 0.67 U/kg [0.15 to 0.30 U/lb]) twice daily, and 3 dogs were receiving a dosage < 0.4 U/kg (0.18 U/lb). In dogs with well-regulated diabetes mellitus, the mean minimum blood glucose concentration (163 ± 89 mg/dL; 95% confidence interval, 100 to 227 mg/dL) was detected 2 hours after administration of glargine insulin and the mean maximum blood glucose concentration (230 ± 95 mg/dL; 95% confidence interval, 64 to 323 mg/dL) was detected 12 hours after administration of glargine insulin. There was no significant difference between mean minimum and mean maximum blood glucose concentrations nor were there significant differences between blood glucose concentrations measured at other time points. Blood glucose concentration < 80 mg/dL was measured at least once in 7 of 10 dogs.

Conclusions and Clinical Relevance—Results of the present study suggested that, in diabetic dogs fed a diet high in insoluble fiber, glargine insulin is a peakless insulin that does not induce a distinct blood glucose concentration nadir. For glargine insulin, 0.3 U/kg (0.136 U/lb) SC twice daily is recommended as an initial dosage.

Abstract

Objective—To evaluate the effects of twice-daily glargine insulin administration in dogs with diabetes mellitus.

Design—Open-label, prospective clinical trial.

Animals—10 dogs with naturally occurring diabetes mellitus.

Procedures—Dogs with poorly regulated or newly diagnosed diabetes mellitus were enrolled if their owners agreed to return them to the hospital at 1- to 3-week intervals for 4 follow-up visits. During each follow-up visit, blood glucose concentrations were measured every 2 hours for at least 10 hours after feeding a diet high in insoluble fiber and after administration of glargine insulin (time 0). The initial glargine insulin dosage was 0.5 U/kg (0.23 U/lb) SC twice daily.

Results—All dogs had well-regulated diabetes mellitus at a mean ± SD of 38 ± 14 days (median, 43 days; range, 7 to 55 days) following study enrollment. At the time diabetes mellitus was well regulated, mean glargine insulin dosage was 0.5 ± 0.15 U/kg (0.23 ± 0.068 U/lb; median, 0.5 U/kg; range, 0.32 to 0.67 U/kg [0.15 to 0.30 U/lb]) twice daily, and 3 dogs were receiving a dosage < 0.4 U/kg (0.18 U/lb). In dogs with well-regulated diabetes mellitus, the mean minimum blood glucose concentration (163 ± 89 mg/dL; 95% confidence interval, 100 to 227 mg/dL) was detected 2 hours after administration of glargine insulin and the mean maximum blood glucose concentration (230 ± 95 mg/dL; 95% confidence interval, 64 to 323 mg/dL) was detected 12 hours after administration of glargine insulin. There was no significant difference between mean minimum and mean maximum blood glucose concentrations nor were there significant differences between blood glucose concentrations measured at other time points. Blood glucose concentration < 80 mg/dL was measured at least once in 7 of 10 dogs.

Conclusions and Clinical Relevance—Results of the present study suggested that, in diabetic dogs fed a diet high in insoluble fiber, glargine insulin is a peakless insulin that does not induce a distinct blood glucose concentration nadir. For glargine insulin, 0.3 U/kg (0.136 U/lb) SC twice daily is recommended as an initial dosage.

Glargine insulina is a human insulin analogue produced through recombinant DNA techniques.1 Glargine differs from human insulin in that the asparagine at position A21 is replaced with glycine, and 2 arginine residues are added to the C-terminal of the B chain at position B30.1 This composition results in low aqueous solubility at neutral pH, and glargine insulin is completely water soluble at a pH of 4.2 The acidic glargine solution forms microprecipitates at the physiologic pH of the subcutaneous space, and the release of glargine insulin from these microprecipitates is slow, prolonged, and relatively constant.1,3 In human patients, these properties of glargine insulin induce serial blood glucose concentrations that are similar to each other without a distinct nadir. Glargine insulin is therefore described as a peakless insulin and is used in human patients with diabetes mellitus to mimic the flat interprandial second phase of normal insulin secretion.1,3

The use of glargine insulin has been reported in 3 dogs with experimentally induced diabetes mellitus and 14 dogs, from 2 studies, with spontaneous diabetes mellitus.4–6 The goal of the study reported here was to further the understanding of and refine the guidelines for the use of glargine insulin in dogs with naturally occurring diabetes mellitus to provide another alternative for insulin treatment of diabetic dogs. We hypothesized that glargine insulin can be used effectively as a twice-daily treatment for dogs with diabetes mellitus.

Materials and Methods

Animals—Dogs examined at the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania from June 2008 to November 2009 with either poorly regulated or newly diagnosed diabetes mellitus were enrolled prospectively in this study. Inclusion criteria were a confirmed diagnosis of diabetes mellitus in addition to owner willingness to return to the hospital for 4 follow-up visits at 1- to 3-week intervals and to feed the dog a prescription dietb high in insoluble fiber and complex carbohydrates.7 During these follow-up visits, dogs had serial blood glucose concentrations measured every 2 hours for at least 10 hours following feeding and insulin administration. The study was approved by the University of Pennsylvania Institutional Animal Care and Use Committee, and all owners provided written consent. The signed consent form stated that the study participation was entirely voluntary and that the owner or attending veterinarian could withdraw the dog from the study at any time.

Diabetes mellitus was diagnosed in dogs on the basis of clinical signs such as polyuria, polydipsia, polyphagia, or weight loss in conjunction with persistent hyperglycemia with glucosuria.8 At the time of enrollment in the study, dogs were considered to have poorly regulated diabetes mellitus if they had polyuria, polydipsia, polyphagia, or weight loss and blood glucose concentration ≥ 200 mg/dL throughout a 10-hour period of blood glucose concentration measurements despite twice-daily SC insulin treatment at a dosage ≥ 0.5 U/kg (0.23 U/lb) every 12 hours.

Dogs with poorly regulated or newly diagnosed diabetes were not enrolled in the study if owners could not commit to the 4 follow-up visits, if the dog refused to eat the prescribed diet during a trial feeding just prior to enrollment, or if owners refused to feed the prescribed diet or sign the consent form.b Dogs that had polyuria, polydipsia, polyphagia, or weight loss and a blood glucose concentration < 200 mg/dL were also not enrolled in the study.

Concurrent disorders—A CBC,c serum biochemical profile,d urinalysis,e and aerobic culture of a urine sample obtained by cystocentesis were performed for all dogs at the time of enrollment into the study and at the time the study was completed to evaluate for the presence of concurrent disorders. Abdominal ultrasonography was also performed at the time of enrollment into the study in all dogs. Acute pancreatitis was diagnosed on the basis of appropriate clinical signs and abdominal ultrasonographic findings of an enlarged irregular hypoechoic pancreas surrounded by a hyperechoic mesentery.9 Additional testing such as ACTH stimulation testing, low-dose dexamethasone suppression testing, or canine pancreatic lipase immunoreactivity measurement was performed and interpreted as previously described, if clinically indicated.9,10 Canine pancreatic lipase immunoreactivity was measured if dogs had vomiting, diarrhea, anorexia, or signs of abdominal pain.

The date of enrollment in the study was defined as the day treatment with glargine insulin was started. Dogs were given glargine insulin (0.5 U/kg, SC, q 12 h) with or immediately following the prescription diet meal.b The time of glargine insulin administration was defined as time 0. Glargine insulin treatment was started only in well-hydrated dogs that were eating their entire prescription diet meal readily and after all clinical signs associated with diabetic ketoacidosis or acute pancreatitis had resolved. Diabetic ketoacidosis was treated as previously described with IV fluid therapy, electrolyte supplementation, and continuous rate infusion of regular insulin IV.11 The prescription diet was introduced as the dog's only food at the time of enrollment into the study and not as a gradual transition from the dog's previous diet. Owners of dogs with newly diagnosed diabetes were educated on insulin administration technique at the time of enrollment into the study.

Follow-up evaluation—Dogs were evaluated during 4 follow-up visits at 1- to 3-week intervals. Dogs were fed and given insulin at home prior to each follow-up visit. Follow-up evaluations included a physical examination and measurement of blood glucose concentrations 2, 4, 6, 8, and 10 hours after insulin administration (time 0).a,b,f Some dogs also had a 12-hour blood glucose concentration measured following time 0, although this was not required for inclusion in the study.

Detailed reporting of owner-perceived clinical signs was recorded at the time of enrollment and at each of the 4 follow-up visits. Polyuria, polydipsia, and polyphagia were defined as suggestive of poorly regulated diabetes mellitus. Owners were specifically asked whether the dog had any vomiting, diarrhea, coughing, or sneezing and whether it had any signs of hypoglycemia such as decreased activity, weakness, in-coordination, disorientation, collapse, fainting, or seizures. Insulin dosage, the time of feeding and insulin administration, body weight, and BCS were recorded at each visit. The endpoint of the study was the time of the fourth follow-up visit and serial blood glucose concentration measurements, regardless of whether the dog had well-regulated diabetes mellitus at that time or earlier. Body condition score was recorded at each visit on a scale of 1 to 9, with a BCS of 1 assigned to emaciated dogs, BCS of 5 assigned to dogs with ideal body weight, and BCS of 9 assigned to grossly obese dogs.

Definition of hypoglycemia—Mild hypoglycemia was defined as a blood glucose concentration between 60 and 79 mg/dL, and severe hypoglycemia was defined as a blood glucose concentration < 60 mg/dL. If blood glucose concentration was < 60 mg/dL, measurement of blood glucose concentration was repeated every 30 minutes until blood glucose concentration was ≥ 60 mg/dL.f

Glargine insulin dosage adjustments—Adjustments in the dosage of glargine insulin were based on clinical signs and blood glucose concentrations. The dosage of glargine insulin was left unchanged in dogs with clinically well-regulated diabetes mellitus in which serial blood glucose concentrations were between 80 and 199 mg/dL during the 10-hour period of blood glucose concentration measurements. Dogs were considered to have clinically well-regulated diabetes mellitus when the owner reported that the dog's thirst, appetite, and activity level were all normal.12,13 The twice-daily dosage of glargine insulin was increased by 0.001 to 0.2 U/kg (0.0005 to 0.09 U/lb) if dogs had poorly regulated diabetes mellitus on the basis of the presence of clinical signs such as polyuria, polydipsia, polyphagia, or weight loss and blood glucose concentration ≥ 200 mg/dL throughout the 10-hour period of blood glucose concentration measurements. The twice-daily glargine insulin dosage was decreased by 0.001 to 0.2 U/kg if any clinical signs suggestive of hypoglycemia were reported by the owner or if measured blood glucose concentration was ever < 80 mg/dL.

Statistical analysis—The Shapiro-Wilk test was used to evaluate continuous variables (blood glucose concentrations, SDs of blood glucose concentrations, and insulin dosage) for normality. Mean ± SD and 95% CI were used to describe normally distributed variables. Mean ± SD, median, and range were reported for non-normally distributed data. The paired t test was used to compare blood glucose concentrations and insulin dosages at various times. A repeated-measures ANOVA was used to assess differences in all blood glucose concentrations measured at all time points during the first follow-up visit and when dogs had well-regulated diabetes mellitus. Proportions and percentages were used to describe categorical variables. Values of P < 0.05 were considered significant for all comparisons. All statistical analyses were performed with a statistical software package.g

Results

Ten dogs were enrolled in the study, and all 10 completed the study. Mean ± SD age of the dogs included in the study was 7.5 ± 1.7 years (median, 8.0 years; range, 4.5 to 10.0 years). Seven of the 10 dogs were neutered males, 2 were neutered females, and 1 was a sexually intact male. Four Labrador Retrievers, 2 Pugs, and 1 each of Miniature Poodle, Bouvier des Flanders, Brussels Griffon, and mixed breed were included in the study.

Mean ± SD weight of the dogs at the time of enrollment in the study was 27.1 ± 15.6 kg (59.6 ± 34.3 lb; median, 34.5 kg [75.9 lb]; range, 6.0 to 45.2 kg [13.2 to 99.4 lb]). Eight of the 10 dogs had a BCS of 4 or 5, and 2 had a BCS of 6 or 7 at the time of enrollment in the study. At the time of the fourth follow-up visit, mean ± SD body weight of the dogs was 27.0 ± 15.7 kg (59.4 ± 34.5 lb; median, 36.8 kg [81.0 lb]; range, 5.7 to 41.2 kg [12.5 to 90.6 lb]). No significant changes in body weight were identified throughout the study. All of the dogs were newly introduced to the study prescription diet and had not been previously treated with this specific diet.

Five of the 10 dogs had newly diagnosed diabetes, and 5 had poorly regulated diabetes at the time of study enrollment. The 5 dogs with poorly regulated diabetes had been treated with insulin for a mean of 1 ± 0.8 years (median, 1 year; range, 0.1 to 2 years).

Four of the 5 dogs with poorly regulated diabetes had been treated with a porcine lente insulin preparation,h and 1 had been treated with human NPH insulin.i Four of the 5 dogs with newly diagnosed diabetes had diabetic ketoacidosis, and 1 had ketosis without acidosis.

Ninety dogs with diabetes mellitus were examined during the study period and were not enrolled in the study mainly because owners were unwilling to return for follow-up visits (52 dogs), but also because dogs had well-regulated diabetes mellitus (28), there was refusal of the prescribed diet by the owner or the dog (7), or there was lack of consent to participate in the study (3).

Blood glucose concentrations—Mean ± SD serial blood glucose concentrations measured at the first follow-up visit were recorded (Figure 1). Blood glucose concentration was measured in all 10 dogs at 2, 4, 6, 8, and 10 hours after insulin administration (time 0) and in 7 dogs at 12 hours after time 0. The mean minimum blood glucose concentration was measured 2 hours after time 0 and was 181 ± 115 mg/dL (95% CI, 99 to 264 mg/dL; median, 193 mg/dL; range, 40 to 353 mg/dL). The mean maximum blood glucose concentration was measured 12 hours after time 0 and was 238 ± 114 mg/dL (95% CI, 133 to 319 mg/dL; median, 232 mg/dL; range, 122 to 377 mg/dL). There was no significant difference between mean minimum and mean maximum blood glucose concentrations nor were there significant (P = 0.34) differences among any of the 57 blood glucose concentrations measured during this visit.

Figure 1—
Figure 1—

Box-and-whisker plots of blood glucose concentrations over time in 10 dogs with naturally occurring diabetes mellitus treated with glargine insulin. Concentrations were measured at the time of the first follow-up visit, 1 to 3 weeks after the initiation of insulin treatment; time 0 represents the time of insulin administration. For each plot, the box represents the interquartile (25th to 75th percentiles) range, the horizontal line within the box represents the median, and circles represent outliers. Blood glucose concentrations were not significantly (P ≥ 0.05) different from each other at any of the time points. Blood glucose concentrations were measured in all 10 dogs at all time points, except at 12 hours after time 0, at which time blood glucose concentration was measured in 7 dogs.

Citation: Journal of the American Veterinary Medical Association 243, 8; 10.2460/javma.243.8.1154

Mean ± SD serial blood glucose concentrations measured at the time dogs had well-regulated diabetes mellitus were recorded (Figure 2). Blood glucose concentration was measured in all 10 dogs at 2, 4, 6, 8, and 10 hours after time 0 and in 6 dogs at 12 hours after time 0. The mean minimum blood glucose concentration was measured 2 hours after time 0 and was 163 ± 89 mg/dL (95% CI, 100 to 227 mg/dL; median, 161 mg/dL; range, 49 to 341 mg/dL). The mean maximum blood glucose concentration was measured 12 hours after time 0 and was 230 ± 95 mg/dL (95% CI, 64 to 323 mg/dL; median, 208 mg/dL; range, 11 to 339 mg/dL). There was no significant difference between mean minimum and mean maximum blood glucose concentrations nor were there significant (P = 0.32) differences among any of the 56 blood glucose concentrations measured during this visit.

Figure 2—
Figure 2—

Box-and-whisker plots of blood glucose concentrations over time for 10 dogs with well-regulated naturally occurring diabetes mellitus treated with glargine insulin. Blood glucose concentrations were not significantly (P ≥ 0.05) different from each other at any of the time points. Blood glucose concentrations were measured in all 10 dogs at all time points, except at 12 hours after time 0, at which time blood glucose concentration was measured in 6 dogs. See Figure 1 for key.

Citation: Journal of the American Veterinary Medical Association 243, 8; 10.2460/javma.243.8.1154

Significant differences between mean blood glucose concentrations measured at the first follow-up visit and at the time diabetes mellitus was well regulated were not detected (Table 1). However, mean variability of blood glucose concentrations (with variability for each dog expressed as the SD of blood glucose concentrations measured during the first 10 hours) at the time of the first follow-up visit (mean ± SD, 103 ± 8 mg/dL) was significantly (P = 0.004) higher than mean variability at the time diabetes mellitus was well regulated (84 ± 21 mg/dL).

Table 1—

Blood glucose concentrations measured in 10 dogs with poorly regulated or newly diagnosed diabetes mellitus treated with glargine at the first follow-up visit and when diabetes mellitus was well regulated.*

Time following time 0 (h)Blood glucose concentration at the first follow-up visitBlood glucose concentration at the time diabetes mellitus was well regulatedPaired t test P value
2181 ± 115 (99–264)163 ± 89 (100–227)0.671
 193 (40–353)161 (49–341) 
4219 ± 109(135–302)197 ± 65 (135–237)0.529
 194 (65–450)188 (83–294) 
6228 ± 97 (158–298)217 ± 71 (167–268)0.739
 209 (61–406)219 (120–320) 
8234 ± 110(161–307)223 ± 67 (175–272)0.739
 234 (55–349)223 (127–340) 
10224 ± 93 (158–291)205 ± 82 (146–264)0.373
 205 (111–374)199 (94–334) 
12*238 ± 114 (133–319)230 ± 95 (64–323)0.685
 232 (122–377)208 (11–339) 

Data are expressed as mean ± SD (95% CI); median (range).

Blood glucose concentration was measured in all 10 dogs at all time points, except that at 12 hours after time 0, it was measured in 7 dogs at the time of the first follow-up visit and in 6 dogs when diabetes mellitus was well regulated. Time 0 was defined as the time of feeding and glargine insulin administration.

Insulin dosage—Mean insulin dosage at the first follow-up visit was 0.5 ± 0.08 U/kg (0.23 ± 0.036 U/lb; median, 0.5 U/kg; range, 0.36 to 0.67 U/kg [0.16 to 0.305 U/lb]) twice daily. Although all dogs were receiving an initial glargine insulin dosage of 0.5 U/kg twice daily at the time of enrollment, only 8 of 10 dogs were still receiving this dosage at the time of the first follow-up visit. While receiving the dosage of 0.5 U/kg twice daily, 1 dog developed seizures, and its dosage was reduced prior to the first follow-up visit to 0.36 U/kg twice daily. In another dog, the owner increased the dosage of insulin to 0.67 U/kg twice daily without consultation. The first follow-up visit was performed at a mean of 13 ± 5 days (median, 10 days; range, 7 to 21 days) following enrollment.

Mean insulin dosage at the time dogs had well-regulated diabetes mellitus was 0.5 ± 0.15 U/kg (0.23 ± 0.068 U/lb; median, 0.5 U/kg; range, 0.32 to 0.67 U/kg [0.145 to 0.305 U/lb]) twice daily and was not significantly (P = 0.9) different from the insulin dosage at the time of the first follow-up visit. At the time dogs had well-regulated diabetes mellitus, the twice-daily glargine insulin dosage was 0.5 U/kg in 4 dogs and > 0.6 U/kg (0.27 U/lb) or < 0.4 U/kg (0.18 U/lb) in 3 dogs each. Dogs had well-regulated diabetes mellitus at a mean of 38 ± 14 days (median, 43 days; range, 7 to 54 days) following enrollment.

Dogs were enrolled in the study for a mean of 57 ± 13 days (median, 53 days; range, 36 to 78 days), at which time each of the dogs had completed 4 follow-up visits. All 10 dogs had well-regulated diabetes mellitus prior to or at the time of completion of the study. Six of the 10 dogs had well-regulated diabetes mellitus on the third follow-up visit, 2 dogs had well-regulated diabetes mellitus on the second visit, and 1 dog each had well-regulated diabetes mellitus on the first or fourth visit.

Adverse effects—Two hundred eighty-one blood glucose concentrations were recorded during the study period, and hypoglycemia was noted at various time points in 7 of the 10 study dogs. Blood glucose concentration < 60 mg/dL was recorded in 13 of 281 (5%) measurements and in 5 of 10 dogs, whereas blood glucose concentration between 60 and 79 mg/dL was recorded in an additional 13 of 281 (5%) measurements and 4 of 10 dogs. Mean blood glucose concentration in the 13 severely hypoglycemic measurements was 38 ± 17 mg/dL (median, 40 mg/dL; range, 11 to 59 mg/dL). Mean blood glucose concentration in the 13 mildly hypoglycemic measurements was 68 ± 6 mg/dL (median, 66 mg/dL; range, 60 to 77 mg/dL). None of the hypoglycemic dogs developed clinical signs associated with hypoglycemia while in the hospital; however, 2 of the 7 dogs in which hypoglycemia was documented at the hospital had a seizure at home, and in one of these dogs, the seizure may have been due to prosencephalic disease. No other adverse effects were noted.

Concurrent disorders—Results of CBC, biochemical profiles, and urinalyses were similar to those previously reported in dogs with diabetes mellitus or diabetic ketoacidosis.8,11 All but 1 of 20 urine samples collected at the time of enrollment and at the completion of the study had no aerobic growth. One dog had a Kluyvera cryocrescens urinary tract infection at the time of enrollment, which resolved with appropriate antimicrobial treatment during the study period. Three dogs were determined to have acute pancreatitis prior to enrollment in the study on the basis of appropriate clinical signs and ultrasonographic findings. Two of these dogs also had canine pancreatic lipase immunoreactivity > 1,000 μg/L, and the third dog had canine pancreatic lipase immunoreactivity of 343 μg/L. Clinical signs of acute pancreatitis resolved prior to enrollment in the study. A fourth dog that had vomiting and colitis prior to enrollment in the study had normal canine pancreatic lipase immunoreactivity. Hyperadrenocorticism was not diagnosed in any of the study dogs. An ACTH stimulation test excluded a diagnosis of hyperadrenocorticism in 5 of the 7 dogs in which it was performed. In 2 dogs in which the ACTH stimulation test was indicative of possible hyperadrenocorticism, a follow-up low-dose dexamethasone suppression test indicated that adrenal function was normal.

Additional concurrent disorders diagnosed in 1 dog each at the time of enrollment in the study included fecal parasitic mesocestoides infection, otitis externa, and an enlarged lymph node characterized cytologically as reactive with an eosinophilic component, hypermature cataracts and anterior uveitis in both eyes, pyoderma, colitis and vomiting, and keratoconjunctivitis sicca with superficial corneal ulcers in both eyes.

One dog had seizures that were initially suspected to be attributable to hypoglycemia, but ultimately, the dog was suspected of having prosencephalic disease. The owner declined brain imaging and further testing, so a definitive diagnosis was not established and additional treatment was not undertaken.

Discussion

Results of the present study suggested that in diabetic dogs fed a diet high in insoluble fiber, glargine insulin is a peakless insulin. There was no significant difference between mean minimum and mean maximum blood glucose concentrations or between any of the blood glucose concentrations measured at other time points. This was true at the time of the first follow-up visit as well as when dogs had well-regulated diabetes mellitus. We therefore concluded that, in dogs, glargine insulin is a peakless insulin, which results in a relatively flat blood glucose concentration curve.

Glargine insulin is the first peakless insulin reported in dogs. Other insulin products such as NPH insulin, porcine lente insulin, and human recombinant protamine zinc insulin produce a blood glucose concentration nadir significantly lower than blood glucose concentrations measured at other times.13–15 The peakless glargine insulin has become an important component of diabetes mellitus treatment in humans because it is able to mimic the flat, basal, interprandial, second phase of insulin secretion.3 Normal physiologic insulin secretion is characterized by a first, rapid, short surge in insulin secretion, immediately following a meal, and a longer flat second phase of insulin secretion between meals.2,16 Glargine, in combination with rapidly acting insulins with a short duration of action administered immediately prior to meals to mimic the first phase of insulin secretion, has served as the basis for the basalbolus insulin treatment in human patients.3 The ability to mimic normal physiologic insulin secretion holds great promise in regard to the long-term outcome of human patients with diabetes.3,17 Future studies in dogs would be needed to investigate the merits of basalbolus insulin treatment, in which glargine insulin would serve as the basal insulin.

One concern over the lack of a detectable difference between blood glucose concentrations measured at different times in the present study is that a significant difference was missed because of the small number of study dogs or a type II statistical error. At the time that this initial study was designed, there were no published data regarding the use of glargine insulin in dogs with naturally occurring diabetes mellitus. Therefore, a power calculation aimed at determining the number of dogs required to detect a significant decrease or increase in blood glucose concentration, induced specifically by glargine insulin, was not possible. However, another study13 following a similar protocol in 10 diabetic dogs fed the same diet but treated with NPH insulin rather than glargine insulin detected several significant differences in blood glucose concentrations at various time points, indicating that a sample size of 10 patients was likely large enough and provided enough statistical power for detection of a difference, if present. A post hoc analysis of the data reported in the NPH insulin study13 revealed that with NPH insulin, the statistical power for detecting a difference in blood glucose concentration with 10 dogs was 98%. Therefore, had glargine been a nadir-inducing insulin, as NPH insulin is, this sample size would likely have been large enough to detect a significant difference in blood glucose concentrations. A post hoc analysis of the data in this study suggested that glargine does not produce a clear blood glucose concentration peak and that 40 dogs would be needed to detect significant differences in blood glucose concentrations. The present study will enable researchers to perform appropriate power calculations for future studies of glargine insulin.

Hypoglycemia was the only adverse effect noted in association with glargine insulin treatment in the present study. Hypoglycemia was documented in 7 of the 10 study dogs and in approximately 10% of the 281 blood glucose concentrations measured. Clinical signs associated with hypoglycemia were not observed in the hospital in any of the study dogs; however, 2 dogs in which hypoglycemia was documented at the hospital had a suspected seizure at home, and in one of these dogs, the seizure may have been due to prosencephalic disease. Hypoglycemia is the most common complication of insulin treatment in humans and dogs, and 1 study14 documented hypoglycemia in 36% of 53 study dogs. The rate of hypoglycemia in the present study was high, and it is therefore recommended that the starting dosage for treatment of diabetic dogs with glargine insulin should be < 0.5 U/kg twice daily. The range of twice-daily insulin dosages administered at the time that diabetes was well regulated was 0.32 to 0.67 U/kg, and 3 dogs were receiving < 0.4 U/kg at that time. Administration of glargine insulin at a dosage of 0.3 U/kg (0.136 U/lb) SC twice daily is therefore recommended as the starting dosage for treatment of diabetic dogs. This dosage will likely have to be increased in some dogs at the time of follow-up visits, but the use of a low starting dosage may also decrease the incidence of hypoglycemia.

The rate of hypoglycemia reported in the present study may have been affected by the fact that if blood glucose concentration was low, a measurement was repeated every 30 minutes, until blood glucose concentration normalized. All low blood glucose concentrations recorded during each episode of hypoglycemia were reported, even if they were measured only 30 minutes apart from each other. Nevertheless, given that hypoglycemia is a potentially fatal complication, overestimating its occurrence is safer than underestimating its occurrence. Future larger studies will help to further assess the rate of hypoglycemia in glargine insulin-treated diabetic dogs.

Another reason for recommending a starting dosage of 0.3 U/kg, SC, every 12 hours is that several study dogs had a concurrent disorder that was likely causing some degree of insulin resistance. Four of the 5 dogs with newly diagnosed diabetes had diabetic ketoacidosis, and 1 had ketosis without acidosis. Three of the dogs with newly diagnosed diabetes had acute pancreatitis. Although diabetic ketoacidosis and clinical signs consistent with acute pancreatitis resolved prior to enrollment in the study, it is possible that in diabetic dogs with no recent history of concurrent disorders contributing to insulin resistance, a starting dosage of 0.5 U/kg twice daily may be too high.

Concerns over an increased incidence of hypoglycemia in human diabetics treated with glargine have been investigated.18,19 Several studies18,19 have shown that despite lower blood glucose concentrations in diabetic patients treated with glargine insulin, compared with those treated with NPH insulin, the rate of hypoglycemia is not increased in glargine insulin-treated diabetic patients. Larger controlled studies of diabetic dogs in which glargine and other insulin products are given following a similar protocol are needed to determine how the rate of insulin-induced hypoglycemia differs with use of glargine versus other insulin products.

Mean blood glucose concentrations at the first follow-up evaluation and at the time dogs had well-regulated diabetes mellitus were not significantly different from each other at any of the time points in this study. This finding supports previous studies,12,20 which found that clinical signs may be superior to blood glucose concentrations when defining well-regulated diabetes in dogs. The results of the present study support the growing body of data that suggest that blood glucose concentrations must be interpreted in view of clinical signs and that well-regulated diabetes mellitus cannot be defined on the basis of blood glucose concentrations alone.

This study also found that after glargine insulin administration, blood glucose concentrations were controlled before clinical signs were regulated. At the time of the first follow-up visit, after a mean glargine insulin treatment duration of 13 ± 5 days, mean minimum and maximum blood glucose concentrations ranged from 181 to 238 mg/dL. However, dogs were not considered to have well-regulated diabetes mellitus until a mean glargine insulin treatment duration of 38 ± 14 days, at which time blood glucose concentrations were not significantly different than at the time of the first follow-up visit.

Although the absolute values of blood glucose concentrations were not significantly different when dogs had well-regulated diabetes mellitus, compared with results at the first follow-up visit in this study, the SD of blood glucose concentrations was significantly (P = 0.004) smaller at the time diabetes mellitus was well regulated, compared with results at the first follow-up visit. This finding suggests that when diabetic dogs are clinically well regulated, the blood glucose concentration curve produced with glargine insulin is significantly less variable than before clinical regulation is optimized.

The endpoint of the present study was the time of the fourth follow-up visit of each dog, regardless of whether the dog had well-regulated diabetes mellitus at that time or earlier. It was decided to define the fourth follow-up visit as the endpoint of the study because at the onset of the study, it was not known whether dogs would achieve well-regulated diabetes mellitus during this time frame, and it was considered unreasonable to continue the study further, should dogs remain poorly regulated for the duration of 4 follow-up visits. Results of this study showed that dogs had clinically well-regulated diabetes mellitus after glargine insulin treatment for a mean duration of 38 ± 14 days, well before the fourth follow-up visit (which occurred 57 ± 13 days following enrollment); however, this was not known at the onset of the study.

The findings of this study are similar to those recently reported in another study5 of 12 dogs with naturally occurring diabetes mellitus in that both studies found that twice-daily glargine insulin treatment is an effective treatment option. The median starting glargine insulin dosage in the 12-dog study was 0.27 U/kg (0.12 U/lb; range, 0.18 to 0.53 U/kg [0.082 to 0.24 U/lb]), SC, every 12 hours, and this dosage was gradually increased to 0.60 U/kg (0.27 U/lb; range, 0.11 to 1.07 U/kg [0.050 to 0.486 U/lb]) every 12 hours.5 It is possible that the wider range and higher glargine insulin dosage required in the 12-dog study, compared with the present study, were due to enrollment of 3 sexually intact females that were neutered within 3 weeks prior to enrollment, 3 dogs with a urinary tract infection, and a lack of diet standardization.6 However, both studies were small, and larger studies will be needed to further the understanding of glargine insulin treatment in dogs.

One of the limitations of the present study was the absence of a control group. However, a protocol for the use of glargine insulin in dogs must be established before it is compared with other insulin products. The findings of this study may enable future studies in which this glargine insulin protocol treatment is compared with other known insulin product treatment protocols.

At about the time that this study was approved and funded, the report of another study4 on the use of glargine insulin in 3 dogs with experimentally induced diabetes mellitus was published. In that study4 investigating dogs with experimentally induced diabetes mellitus, an artificial pancreas apparatus was set to maintain blood glucose concentrations between 68 and 90 mg/dL for 24 hours, following a single glargine insulin injection of 0.5 U/kg. The study4 also investigated the use of combined NPH and glargine insulin for 6 days. The authors concluded that, because hypoglycemia occurred, the insulin doses tested were far from ideal for use in a clinical environment.4 Therefore, that study4 was not used to establish the protocol used in the present study, which was designed to investigate dogs with naturally occurring diabetes mellitus in a clinical rather than a laboratory setting.

The study is further limited in that 2 new variables, a new insulin product and a new diet, were introduced at the same time, and it is not possible to distinguish the effect of one intervention from the effect of the other. Therefore, the conclusions of this study are limited to dogs in which treatment is optimized by feeding the specific study diet,b which is high in insoluble fiber. It is possible that glargine insulin requirements and the effect of glargine insulin on blood glucose concentration are different in dogs fed another diet, and this may explain the difference between the results of this study and the results of another study6 in which diet was not standardized and the effect of glargine insulin was not predictable. The present study was designed to introduce both the new dietb and the new insulin product at the same time, to optimize the treatment of diabetes mellitus. High insoluble dietary fiber has been shown to improve glycemic control in dogs with diabetes mellitus,7 and withholding a beneficial treatment option for the sake of evaluating only glargine insulin may not have met with approval by our university's animal care and use committee. Offering all of the study dogs the same diet also increased standardization of the study population.

Another study limitation was that adrenal axis testing and measurement of canine pancreatic lipase immunoreactivity were performed only in dogs in which clinical signs indicated a possibility of hyperadrenocorticism or acute pancreatitis. This protocol was chosen to minimize the risk of false-positive test results in dogs that did not have appropriate clinical signs, but it may have led to underdetection of these concurrent disorders.

On the basis of this study, we concluded that glargine insulin administered SC twice daily is an effective mode of treatment for dogs with naturally occurring diabetes mellitus and may be used as an alternative to other insulin preparations that have been shown to be effective in treatment of diabetes mellitus in dogs.13–15 Administration of 0.3 U of glargine insulin/kg, SC, twice daily is recommended as a starting dosage, although some dogs will require a gradual increase in dosage for their diabetes to become well regulated.

ABBREVIATIONS

BCS

Body condition score

CI

Confidence interval

NPH

Neutral protamine Hagedorn

a.

Lantus, Sanofi-Aventis US LLC, Bridgewater, NJ.

b.

W/D diet, Hill's Pet Nutrition Inc, Topeka, Kan.

c.

Hematology analyzer, Celldyne 3500, Abbott Laboratories, Abbott Park, Ill.

d.

Chemistry analyzer, Kodak Ektachem 250, Eastman Kodak Co, Rochester, NY.

e.

Urinalysis N-Multistix SG, Bayer Corp, Elkhart, Ind.

f.

Accu-Check Advantage, Roche Diagnostics, Indianapolis, Ind.

g.

Stata, version 11.0 for Windows, Stata Corp College Station, Tex.

h.

Porcine insulin zinc suspension, Intervet/Schering-Plough Summit, NJ.

i.

Humulin-N, Eli Lilly and Co, Indianapolis, Ind.

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