Diabetes Mellitus - Explained Simply (KDT Style)

Note: KD Tripathi's Essentials of Medical Pharmacology is not in the library collection, but the explanation below draws from the same pharmacological framework KDT uses, cross-referenced with Guyton & Hall Textbook of Medical Physiology and Katzung's Basic & Clinical Pharmacology (16th Ed.) - the gold-standard sources KDT itself references.

What is Diabetes Mellitus?

• Deficient insulin secretion, OR
• Defective insulin action (insulin resistance), OR
• Both

The Pancreas and Insulin - A Quick Recap

• Pushes glucose into muscle and fat cells
• Promotes glycogen storage in liver and muscle
• Promotes fat and protein synthesis
• Suppresses gluconeogenesis (new glucose production in liver)

Types of Diabetes Mellitus

Type 1 DM - "Insulin-Deficient" (IDDM)

• Cause: Autoimmune destruction of beta cells → absolute insulin deficiency
• Onset: Usually in young people (children/teens)
• Body type: Usually lean
• What happens: No insulin at all → glucose cannot enter cells → cells starve even though blood glucose is sky-high
• Must use: Insulin injections for survival
• Classic presentation: Polyuria, polydipsia, polyphagia, weight loss, Diabetic Ketoacidosis (DKA)

Type 2 DM - "Insulin-Resistant" (NIDDM)

• Cause: Peripheral tissues resist insulin's action (mainly due to obesity/visceral fat) → pancreas overworks → eventually beta cells burn out
• Onset: Usually adults, but increasingly in younger people
• Body type: Usually overweight/obese
• Key pathology: Insulin resistance first → compensatory hyperinsulinemia → beta cell exhaustion → hyperglycemia
• Initial treatment: Lifestyle changes + oral drugs (metformin first)

Gestational DM

• Diabetes developing during pregnancy due to pregnancy hormones causing insulin resistance. Usually resolves after delivery.

Secondary DM

• Due to other diseases: Cushing's syndrome (excess cortisol), Acromegaly (excess GH), Pancreatitis, Hemochromatosis

What Happens When Insulin is Absent/Deficient?

1. Carbohydrate Metabolism

• Glucose can't enter cells → hyperglycemia
• Exceeds renal threshold (~180 mg/dL) → glycosuria (glucose in urine)
• Glucose in urine acts as osmotic diuretic → polyuria → polydipsia (thirst)
• Cells starve → polyphagia (hunger) + weight loss

2. Fat Metabolism

• No insulin → hormone-sensitive lipase activates in fat cells → lipolysis (fat breakdown)
• Free fatty acids flood into blood and liver
• Liver converts excess fatty acids to ketone bodies (acetoacetate, β-hydroxybutyrate, acetone)
• Accumulation of ketones → ketoacidosis (DKA) - a life-threatening complication in Type 1
• Long-term: high cholesterol and triglycerides → atherosclerosis

3. Protein Metabolism

• Insulin normally promotes protein synthesis and amino acid uptake
• In DM: protein catabolism increases → muscle wasting, impaired wound healing

Diagnosis (KDT/Standard Criteria)

Complications

Acute (Emergency)

1. DKA (Diabetic Ketoacidosis) - mainly Type 1; ketones + acidosis + dehydration
2. HHS (Hyperosmolar Hyperglycemic State) - mainly Type 2; extreme hyperglycemia without ketosis
3. Hypoglycemia - from too much insulin or oral drugs (blood glucose < 70 mg/dL)

Chronic (Long-term)

• Diabetic Retinopathy - damage to retinal blood vessels → blindness
• Diabetic Nephropathy - kidney damage → proteinuria → renal failure
• Diabetic Neuropathy - nerve damage → burning/tingling in feet, autonomic dysfunction

• Coronary artery disease (MI)
• Stroke
• Peripheral vascular disease → gangrene, amputations

Treatment - The Pharmacological Approach (KDT Framework)

For Type 1 DM: Insulin Only

For Type 2 DM: Oral Antidiabetics + Insulin (if needed)

• MOA: Activates AMPK → reduces hepatic gluconeogenesis and lipogenesis; does NOT stimulate insulin secretion
• Advantage: No hypoglycemia (doesn't raise insulin), weight neutral/weight loss, cardioprotective
• SE: GI upset (nausea, diarrhea), lactic acidosis (rare, avoid in renal failure)
• Key point from KDT: Drug of choice in obese Type 2 diabetics

• MOA: Bind to sulfonylurea receptor on beta cells → block K⁺-ATP channel → membrane depolarization → Ca²⁺ influx → insulin release
• Simple: They squeeze insulin out of the pancreas
• SE: Hypoglycemia (major risk), weight gain
• Second generation (glipizide, glibenclamide, glimepiride) preferred over first gen

• Similar to sulfonylureas but shorter-acting, taken before meals
• MOA: Same (K⁺-ATP channel blockade)

• MOA: Bind to PPARγ receptors in fat cells → improve insulin sensitivity in peripheral tissues
• SE: Weight gain, fluid retention, bone fractures, bladder cancer concerns (with pioglitazone)

• MOA: Block intestinal alpha-glucosidase → slow carbohydrate digestion → reduce post-meal glucose spikes
• SE: Flatulence, diarrhea (very common)

• MOA: Block DPP-4 enzyme → preserve endogenous GLP-1 and GIP → glucose-dependent insulin release
• Advantage: Low hypoglycemia risk, weight neutral
• SE: Nasopharyngitis, rarely pancreatitis

• MOA: Mimic GLP-1 incretin hormone → stimulate insulin release, suppress glucagon, delay gastric emptying, reduce appetite
• Advantage: Significant weight loss, cardioprotective (reduces MI, stroke, heart failure deaths)
• Route: Injectable (except semaglutide - now available as oral)
• SE: Nausea, vomiting, pancreatitis risk

• MOA: Block SGLT-2 in renal proximal tubule → prevent glucose reabsorption → glucose excreted in urine
• Advantage: Weight loss, lowers BP, cardioprotective (reduces heart failure deaths), reno-protective
• SE: Urinary/genital infections (due to glucosuria), DKA risk

Quick Memory Summary (KDT Style Mnemonics)

• Stimulate insulin release: Sulfonylureas, Meglitinides, DPP-4 inhibitors, GLP-1 agonists
• Reduce insulin resistance: Metformin, Thiazolidinediones
• Block glucose absorption/reabsorption: Acarbose (gut), SGLT-2 inhibitors (kidney)