Chapter 44: Diabetes Mellitus – Drug Therapy & Insulin Use

The chapter identifies diagnostic criteria using Hemoglobin A1c (A1c), Fasting Plasma Glucose (FPG), and the Oral Glucose Tolerance Test (OGTT), establishing thresholds for normoglycemia, prediabetes (impaired fasting glucose/impaired glucose tolerance), and confirmed diabetes. Pathophysiologically, Type 1 diabetes involves the autoimmune destruction of pancreatic beta cells, necessitating insulin replacement, while Type 2 diabetes, which accounts for up to 95% of cases, is driven primarily by tissue insulin resistance and subsequent impaired secretion and increased hepatic glucose production. Treatment goals are highly individualized but generally target an A1c below 7.0%, alongside tight control of blood pressure and lipids, aiming to prevent long-term microvascular complications like retinopathy and nephropathy, and macrovascular issues. Initial treatment for Type 2 diabetes always incorporates intensive lifestyle changes, often combined with first-line monotherapy, typically metformin, a biguanide that lowers hepatic glucose production without causing hypoglycemia or weight gain when used alone. If glycemic goals are unmet, second- or third-line agents are added, selected based on efficacy, cost, patient preferences, and the presence of cardiovascular (CV) or renal comorbidities. Drug classes discussed include sulfonylureas and meglitinide analogs, which stimulate insulin release; thiazolidinediones (TZDs), which enhance insulin sensitivity; alpha-glucosidase inhibitors, which delay carbohydrate absorption; and newer injectable and oral agents. The newest therapies, Glucagon-Like Peptide Receptor Agonists (GLP1-RAs) and Sodium-Glucose Co-Transporter 2 Inhibitors (SGLT-2is), are especially highlighted for their proven benefits in reducing CV and renal risks, making them preferred choices for patients with established ASCVD or Chronic Kidney Disease. Insulin therapy, which replaces the physiologic basal and prandial insulin profile, remains the cornerstone for Type 1 management and is often initiated in Type 2 patients when high A1c persists despite combination oral therapy. Effective patient education, including Self-Monitoring of Blood Glucose (SMBG) and instruction on acute complications like hypoglycemia, is essential for successful diabetes self-management.