© American Diabetes Association ®, Inc., 2005
A Real-World Approach to Insulin Therapy in Primary Care Practice
Type 2 diabetes is a progressive disease characterized by relentless deterioration of pancreatic ß-cell function.1 With the increasing incidence of type 2 diabetes, especially among younger individuals who will live longer with their disease, more patients will develop severe insulin deficiency and require insulin replacement. Because primary care providers see the vast majority of patients with type 2 diabetes, they may soon find themselves overwhelmed with insulin-requiring patients. This article provides some practical guidelines for initiating insulin therapy in primary care practice. It is important to remember, however, that these are general guidelines and that management should be individualized for each patient. WHY INSULIN THERAPY? Some primary care providers may be apprehensive about using insulin in patients with type 2 diabetes. Wallace and Matthews2 have gone so far as to suggest that patients and providers have often "colluded in implicit and unspoken contracts to continue oral agents for as long as possible."
Concerns about hypoglycemia and patient willingness and/or ability to
inject insulin are good reasons why many providers may approach insulin
therapy with caution. Compounding this reluctance is the perception that
insulin therapy is too complex to manage in a busy primary care practice;
prescribing information provided by manufacturers has been somewhat vague
regarding initial dosing and titration. Because of these factors, providers
may delay in making the necessary transition from oral agents to insulin.
Indeed, recent evidence suggests that the hemoglobin A1c (A1C)
result that triggers glucose-lowering action is
Early and Aggressive Intervention Matters New data from the Epidemiology of Diabetes Interventions and Complications (EDIC) study highlight the importance of early intervention to aggressively lower glucose.8 The EDIC study is an ongoing effort that follows the cohort from the Diabetes Control and Complications Trial (DCCT).13 In the EDIC study, glycemic levels no longer differed substantially between the two original DCCT treatment groups at 7 years. However, subjects who had been intensively treated during the DCCT showed significant decreases in risk for nephropathy and retinopathy compared with subjects from the conventional treatment arm. In other words, the benefits of 6.5 years of intensive treatment during the DCCT have extended well beyond the time of intensive therapy.
Insulin May Have a Protective Quality
New Insulin Analogs More Closely Match Normal Physiology
New Evidence Links Glucose Excursions to Cardiovascular Risk
Chiasson et
al.29 showed that
addressing postprandial hyperglycemia using an
Patients Will Eventually Need Insulin Therapy Unfortunately, insulin therapy too often is used as a "punishment" for above-target hyperglycemia. A better approach would be to explain to patients early in the course of their disease, instead of at the end, the natural history of insulin deficiency in type 2 diabetes.2 WHO SHOULD BE STARTED ON INSULIN? Initiating therapy with oral agents is a reasonable approach to take with most patients, the exception being patients with extreme hyperglycemia (fasting plasma glucose > 250 mg/dl).32 These patients require insulin, even basal-bolus insulin therapy, to lower glucose levels. Otherwise, starting with oral therapy can be very effective, especially in patients with a short duration of diabetes and, thus, relatively adequate ß-cell function. However, clinicians often wait too long to move patients from oral therapy to insulin.33,34 In the UKPDS, only 33% of patients treated with metformin and sulfonylurea had an A1C < 7% after 3 years of treatment.35 When determining whether a patient should be put on insulin therapy, it is helpful to look to the guidelines for glycemic control. The American Diabetes Association (ADA)36 and American College of Endocrinology (ACE)37 publish goals for A1C, postprandial glucose, and fasting/preprandial glucose (Table 1). Most patients who are unable to achieve these goals using oral agents are candidates for insulin therapy. Table 2 lists the more commonly used insulins, along with information about their peak activity.
The key to making this determination is timely (preferably weekly) titration of dosages until either glucose targets are met or maximum effective dosages fail to achieve target levels. For example, weekly titration of sulfonylurea dosages, in combination with daily fasting glucose data (provided by the patient), will show whether monotherapy with sulfonylurea can provide adequate glycemic control. If not, the addition and timely titration of a second agent (metformin or a thiazolidinedione) over the next 2 months, along with continued blood glucose monitoring, will show whether combination oral therapy can provide adequate glycemic control. If not, insulin therapy is clearly warranted and should be promptly initiated (Figure 1).
Although it may be tempting to add a third oral agent, clinicians must consider the added cost and potential side effects associated with triple oral therapy. A recent study by Schwartz et al.38 showed that a regimen of premixed insulin in combination with metformin was as effective as but much less expensive than triple oral therapy; a high percentage of subjects (16.3%) from the triple oral agent treatment group did not complete the regimen because of a lack of efficacy or side effects. HOW TO START PATIENTS ON INSULIN Starting patients on insulin does not have to be difficult. This section presents an approach that takes the uncertainty and complexity out of initiating insulin therapy in patients with type 2 diabetes. Figure 1 provides an algorithm for transition from oral therapy to insulin.
Match the Regimen to the Patient Patients who are reluctant to do basal-bolus management initially often make the transition to multiple daily injection (MDI) regimens after gaining confidence in their ability to safely and effectively use insulin through less intensive regimens. Table 3 presents common insulin regimens based on patient clinical status and lifestyle characteristics.
Although regimens for once-daily glargine and once-daily and twice-daily premixed insulin are listed, it is important to note that recent studies comparing once-daily regimens to twice-daily regimens have demonstrated significant differences between the two approaches.39-41
One study showed that twice-daily premixed insulin (25% lispro/75% NPL)
provided lower A1C levels compared with once-daily glargine when patients were
randomized to one or the other insulin regimen in addition to existing
metformin therapy39
Results also showed a smaller rise in postprandial glucose levels and a higher
proportion of patients achieving an A1C of When postprandial glucose is not adequately controlled by combination therapy using basal insulin and oral agents, a twice-daily regimen using a premixed insulin preparation (prebreakfast, presupper) is preferred. Clinicians can start patients on once-daily injections at the evening meal and add the second injection as needed. Rapid-acting analog premixed insulin is an option if the patient eats small lunches or misses lunch regularly. Although no definitive studies have looked at this issue, the authors agree that for individuals eating large lunches (e.g., > 40% of their total daily calories), a better premix insulin would be 70% NPH/30% regular insulin. The problem with this regimen, however, is that the lunchtime meal needs to be consumed at about the same time each day to avoid hypoglycemia. Basal-bolus insulin therapy may be required for patients with glucose toxicity (fasting plasma glucose > 250 mg/dl).42 Basal-bolus insulin therapy can be continued or modified after glucose returns to near-normal levels. Additionally, basal-bolus insulin management should be presented as the next option if patients are unable to achieve targets with a premixed insulin regimen. This will be the rule for patients with more severe insulin deficiency.
Start Low and Titrate Steadily
The Treat-to-Target
study44 used a
starting dose of 10 units/day with glargine or human NPH at bedtime; mean
daily dosages at end point adjusted for body weight were 0.48 units/kg for
glargine and 0.42 units/kg for NPH in those patients who were maintained on
one or two oral agents throughout the study. This is equivalent to The differences in average dosages at end point reported in these studies resulted from differences in baseline A1C levels, durations of diabetes, and overall levels of insulin resistance in the study subjects. Nevertheless, these studies show 10 units/injection to be a safe starting dose for once-daily and twice-daily insulin regimens (Table 4).
It is important to note that although glargine can be taken at any time during the day, it should be injected at the same time every day. Patients should document all results from self-monitoring of blood glucose (SMBG) and insulin doses in their logbooks when starting or adjusting insulin. Glucose meter downloading is another excellent tool for review of SMBG data.45
Monitor and Adjust Therapy Until Targets are Achieved
Working with this schedule, patients measure blood glucose once or twice daily (prebreakfast, presupper) depending on their regimen. Based on these blood glucose data reported by the patient, the clinician can then make step-wise adjustments in response to the average glucose values. Prebreakfast dosage adjustments are based on presupper glucose results, whereas presupper dosage adjustments are based on prebreakfast glucose values. For example, in a patient on 10 units of premixed insulin twice daily who reports prebreakfast glucose values ranging from 148 to 175 mg/dl over the past 3-7 days, the appropriate adjustment would be an additional 4 units of insulin before supper. Another key aspect of insulin titration is timely adjustment. As with oral therapy, clinicians often wait too long to make adjustments in insulin dosages, allowing excessive glycemic exposure to persist for months (or years, in some cases). A major obstacle to timely insulin adjustment is primarily the logistics of communicating with the patient. Table 6 presents some options for patient follow-up that may expedite achieving glycemic targets on timely basis. Diabetes education is a crucial aspect of patient care and is recommended for all patients, particularly those who are self-adjusting their insulin dosages.
If patients are not at goal after 3-6 months of therapy or if recurrent hypoglycemia limits titration, consider changing the regimen. Table 7 presents strategies for making this transition.
When assessing the need to change regimens, it is important to understand
and consider the impact of fasting glucose and postprandial glucose on overall
glycemic control. Monnier et
al.47 recently
published findings that showed a variable relationship between fasting and
glucose based on current A1C levels. As shown in
Figure 2, the report revealed
that the relative contribution of fasting glucose to overall glycemia is
Knowing the relative contribution of fasting and postprandial glucose to A1C allows clinicians to make more informed decisions about therapy. For example, if a patient's A1C is at 7.5%, adjustment should focus on lowering postprandial glucose; adding basal insulin will not directly address postprandial hyperglycemia. Although the addition of basal insulin will improve the overall A1C, as shown in the Treat-to-Target study,44 it will not lower the degree of postprandial excursions. Only meal plan modification or prandial insulin will address this issue. Figure 3A illustrates how addressing fasting glucose can initially lower fasting levels and even improve postprandial excursions by reducing glucotoxicity and thus improving ß-cell function. However, once fasting glucose levels are normalized, increasing the basal dosage will not adequately address the remaining postprandial hyperglycemia (Figure 3B). Therefore, a regimen that addresses both fasting and postprandial hyperglycemia is needed (Figure 3C).
CONCLUSION Insulin therapy in the treatment of type 2 diabetes offers significant advantages in efficacy and outcomes. However, unfounded fear of hypoglycemia and uncertainties regarding initial dosage and titration have been key obstacles for many providers when making the decision to initiate insulin treatment in their patients with type 2 diabetes. Given the progressive nature and increasing incidence of type 2 diabetes, more patients will be faced with severe insulin deficiencies in their lifetimes. It is hoped that the information and recommendations provided in this article will help primary care providers become more effective in their management of patients with type 2 diabetes. Acknowledgments The authors gratefully acknowledge support from Eli Lilly in funding the expenses related to developing this article. Footnotes Irl B. Hirsch, MD, is a professor of medicine in the Division of Metabolism, Endocrinology, and Nutrition at the University of Washington Medical Center in Seattle. Richard M. Bergenstal, MD, is executive director of the International Diabetes Center and a clinical professor at the University of Minnesota, both in Minneapolis. Christopher G. Parkin, MS, is a medical writer and consultant to professional medical organizations and healthcare companies and president of CGParkin Communications in Carmel, Ind., Eugene E. Wright, Jr., MD, is medical director of Primary Care and Specialty Practices of Cape Fear Valley Health System in Fayetteville, N.C. John B. Buse, MD, PhD, is an associate professor at the University of North Carolina School of Medicine in Chapel Hill, where he is the division chief of General Medicine and director of the Diabetes Care Center. He is also an associate editor of Clinical Diabetes. Notes of disclosure: Dr. Hirsch has received consulting fees or honoraria for speaking engagements from Eli Lilly, Novo Nordisk, and Sanofi-Aventis Pharmaceuticals. He also receives research support from Mannkind Corporation. Dr. Bergenstal has served on advisory panels for, received consulting fees or honoraria from, and received research support from Eli Lilly, Novo Nordisk, and Sanofi-Aventis Pharmaceuticals. Mr. Parkin has received consulting fees from Abbott Diabetes Care, Bayer Diagnostics, Eli Lilly, EMD Pharmaceuticals, Roche Diagnostics, and Sanofi-Aventis Pharmaceuticals. Dr. Wright has served on advisory panels and received consulting fees or honoraria from Eli Lilly and Amylin Pharmaceuticals. The University of North Carolina has received honoraria related to Dr. Buse's speaking engagements for Abbott, Pfizer, and Eli Lilly; grant support related to his research activities from Bristol-Myers Squibb, Novartis Pharmaceuticals, and Pfizer; and consulting fees related to his formal advisory activities from Amylin Pharmaceuticals, BD Research Laboratories, Eli Lilly, Merck, and Bristol-Myers Squibb. All of these companies manufacture pharmaceutical products for the treatment of diabetes. REFERENCES 1 Maedler K, Donath MY: Cells in type 2 diabetes: a loss of function and mass. Horm Res 62 (Suppl. 3):67 -73, 2004 2 Wallace TM, Matthews DR: Poor glycaemic control in type 2 diabetes: a conspiracy of disease, suboptimal therapy and attitude. Q J Med93 : 369-374,2000 3 Brown JB, Nichols GA: Slow response to loss of glycemic control in type 2 diabetes mellitus. Am J Manag Care 9:213 -217, 2003[Medline] 4 Roach P, Koledova E, Metcalfe S, Hultman C, Milicevic Z, the Romania/Russia Mix25 Study Group: Glycemic control with Humalog Mix25 in type 2 diabetes inadequately controlled with glyburide. Clin Ther 23:1732 -1744, 2001[Medline] 5 Niskanen L, Jensen LE, Rastam J, Nygaard-Pedersen L, Erichsen K, Vora JP: Randomized, multinational, open-label, 2-period, crossover comparison of biphasic insulin aspart 30 and biphasic insulin lispro 25 and pen devices in adult patients with type 2 diabetes mellitus. Clin Ther26 : 531-540,2004[Medline] 6 Abraira C, Colwell JA, Nuttall FQ, Sawin CT, Nagel NJ, Comstock JP, Emanuele NV, Levin SR, Henderson W, Lee HS: Veterans Affairs Cooperative Study on glycemic control and complications in type II diabetes (VA CSDM): results of the feasibility trial. Diabetes Care 18:1113 -1123, 1995[Abstract] 7 Henry RR, Gumbiner B, Ditzler T, Wallace P, Lyon R, Glauber HS: Intensive conventional insulin therapy for type II diabetes: metabolic effects during a 6-mo outpatient trial. Diabetes Care 16:21 -31, 1993[Abstract]
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