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Diabetes Pharmacotherapy: A Practical Drug Guide

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First: Set the Glycemic Target (HbA1c)

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TYPE 2 DM — Drug Selection Framework

Step 1: Start with Metformin (unless contraindicated)

• Mechanism: Decreases hepatic glucose output (activates AMPK), improves insulin sensitivity
• Dose: Start 500 mg with meals, titrate up to 2000–2550 mg/day
• Key benefits: Weight neutral to weight loss, no hypoglycemia, cheap, CV-neutral
• Contraindication: eGFR < 30 mL/min (hold if eGFR 30–45), IV contrast procedures, severe liver disease
• Side effect: GI upset (take with food); rare lactic acidosis

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Step 2: Add a Second Agent Based on the Patient's Comorbidities

🫀 Patient with Established CVD or High CV Risk → Add GLP-1 Receptor Agonist or SGLT2 Inhibitor

🫁 Patient with Heart Failure → SGLT2 Inhibitor (first choice)

• Empagliflozin (approved for both HFrEF and HFpEF)
• Dapagliflozin (approved for HFrEF)
• Mechanism beyond glucose: inhibit NHE, reduce cardiac preload, diuretic effect

🩺 Patient with CKD → SGLT2 Inhibitor + consider GLP-1 agonist

• SGLT2 inhibitors slow progression of diabetic nephropathy
• Finerenone (non-steroidal MRA) is now also used in diabetic CKD with albuminuria

⚖️ Patient Who Needs Weight Loss → GLP-1 agonist or SGLT2 inhibitor

• Semaglutide (Ozempic/Wegovy) produces the most weight loss among GLP-1s
• GIP/GLP-1 dual agonist: Tirzepatide (Mounjaro) — superior HbA1c reduction and weight loss

💰 Cost-Conscious / No Comorbidities → Sulfonylurea or Pioglitazone

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Overview of All Drug Classes

1. Metformin (Biguanide)

• ↓ hepatic glucose output
• First-line for T2DM
• Avoid in severe renal/liver failure

2. Sulfonylureas

• ↑ insulin secretion (close K⁺ channels on β-cells → depolarization → insulin release)
• Glipizide, Glimepiride preferred over Glyburide
• Risk: Hypoglycemia, weight gain

3. SGLT2 Inhibitors ("gliflozins")

• Empagliflozin, Dapagliflozin, Canagliflozin
• Block glucose reabsorption in the proximal tubule → glycosuria
• Benefits: HbA1c ↓, weight ↓, BP ↓, heart failure benefit, CKD protection
• Side effects: UTI/genital mycotic infections, DKA (rare, even euglycemic), volume depletion
• Avoid if eGFR < 20–30 (glucose-lowering effect lost, but cardiac/renal benefit may persist)

4. GLP-1 Receptor Agonists

• Semaglutide (weekly SC or oral), Liraglutide (daily SC), Dulaglutide (weekly SC), Exenatide
• Mechanism: Stimulate insulin secretion glucose-dependently, suppress glucagon, delay gastric emptying, reduce appetite
• Benefits: Weight loss, CV protection, no hypoglycemia (when used alone)
• Side effects: Nausea, vomiting (especially on initiation), pancreatitis (rare)
• Contraindicated in personal/family history of medullary thyroid carcinoma or MEN2

5. DPP-4 Inhibitors ("gliptins")

• Sitagliptin, Saxagliptin, Linagliptin, Alogliptin
• Inhibit DPP-4 → ↑ endogenous GLP-1 → modest HbA1c ↓ (~0.5–0.8%)
• Weight neutral, low hypoglycemia risk, well tolerated
• Good for elderly patients
• Note: Saxagliptin associated with ↑ HF hospitalization — avoid in HF

6. Thiazolidinediones (TZDs)

• Pioglitazone (Rosiglitazone largely withdrawn)
• PPAR-γ agonist → improve insulin sensitivity in muscle/fat/liver
• Avoid in heart failure (fluid retention), osteoporosis risk
• Pioglitazone may have modest CV benefit (PROACTIVE trial)

7. Alpha-Glucosidase Inhibitors

• Acarbose, Miglitol
• Delay carbohydrate absorption → blunt postprandial glucose spikes
• GI side effects (flatulence, diarrhea) limit use
• Modest HbA1c reduction (~0.5%)

8. Meglitinides (Glinides)

• Repaglinide, Nateglinide
• Short-acting insulin secretagogues; taken with meals
• Useful when meals are irregular
• Risk of hypoglycemia (less than sulfonylureas)

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TYPE 1 DM — Always Insulin

• 1 basal injection/day + rapid-acting insulin before each meal
• Dose the bolus to match carbohydrate intake (insulin-to-carb ratio)

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Insulin in TYPE 2 DM

• HbA1c > 10–12% at diagnosis with symptoms
• Oral agents fail to achieve target
• Acute illness, surgery, pregnancy, hospitalization

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Quick Decision Summary

T2DM diagnosed?
    │
    ▼
Metformin (unless CrCl < 30 or contraindicated)
    │
    ├─► Established CVD? → GLP-1 agonist (Semaglutide) or SGLT2i (Empagliflozin)
    │
    ├─► Heart failure? → SGLT2 inhibitor
    │
    ├─► CKD? → SGLT2 inhibitor (+ finerenone if albuminuria)
    │
    ├─► Needs weight loss? → GLP-1 agonist / Tirzepatide
    │
    ├─► Cost-sensitive? → Sulfonylurea (Glipizide/Glimepiride)
    │
    └─► HbA1c still uncontrolled? → Add basal insulin

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Key Pitfalls to Avoid

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10 Case Scenarios: Diabetes Drug Treatment — Basics to Advanced

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🟢 CASE 1 — The Basics: Newly Diagnosed T2DM, Healthy Young Adult

• Fasting glucose: 145 mg/dL
• HbA1c: 7.4%
• eGFR: 95 (normal kidneys)
• No heart disease, no other illness

Start with lifestyle + Metformin.

• Decreases hepatic glucose production
• Improves insulin sensitivity in muscles
• Does NOT cause hypoglycemia
• Causes modest weight loss
• Cheap, proven safe for 60+ years
• ADA consensus: "Metformin is the first-line therapy and should be started at the time of diagnosis" — Goodman & Gilman's, p. 1061

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🟢 CASE 2 — T2DM with Obesity, Wants to Lose Weight

Add a GLP-1 receptor agonist — specifically Semaglutide or Liraglutide.

• GLP-1 agonists suppress appetite and delay gastric emptying → significant weight loss (5–15% body weight)
• Glucose-dependent insulin release → low hypoglycemia risk
• HbA1c reduction: 1–1.5%
• "GLP-1 agonists are approved for use in patients with obesity and diabetes" — Katzung, p. 343

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🟢 CASE 3 — T2DM with No Money / Limited Resources

Add a Sulfonylurea — specifically Glipizide or Glimepiride.

• Very cheap — costs pennies per day
• Highly effective: HbA1c reduction of 1–2%
• Mechanism: Closes K⁺-ATP channels on β-cells → depolarization → insulin release

• Hypoglycemia — tell the patient to always carry sugar (juice, candy)
• Weight gain ~2–3 kg
• Do NOT use Glyburide in elderly — it has active metabolites that accumulate, causing prolonged hypoglycemia

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🟡 CASE 4 — T2DM + Established Heart Disease (Post-MI)

Add an SGLT2 inhibitor or GLP-1 agonist — both reduce cardiovascular death.

• EMPA-REG OUTCOME trial showed empagliflozin reduced CV mortality by 38% and HF hospitalization by 35%
• "GLP-1 agonists have been shown to reduce deaths from cardiovascular causes as well as rates of MI, nonfatal stroke" — Katzung, p. 343
• "For individuals with established ASCVD, a GLP-1 receptor agonist or SGLT-2 inhibitor should be added early" — Goodman & Gilman's, p. 1061

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🟡 CASE 5 — T2DM + Chronic Kidney Disease (CKD)

Reduce Metformin dose + Add SGLT2 inhibitor for kidney protection.

• Metformin: Reduce to 500–1000 mg/day (acceptable down to eGFR 30; hold if < 30)
• Empagliflozin or Dapagliflozin 10 mg/day

• Reduces intraglomerular pressure by causing afferent arteriolar vasoconstriction
• DAPA-CKD trial: Dapagliflozin reduced eGFR decline and kidney failure by 44%
• "SGLT2 inhibitors also slow development of chronic kidney disease" — Katzung, p. 343

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🟡 CASE 6 — T2DM + Heart Failure

• ❌ Pioglitazone (TZD) — causes fluid retention → worsens heart failure
• ❌ Saxagliptin — associated with increased HF hospitalization
• ❌ Large IV fluids

SGLT2 inhibitor is the star drug here.

• "Empagliflozin and dapagliflozin have been shown to reduce mortality and hospitalizations for heart failure in patients with or without type 2 diabetes" — Katzung, p. 343
• Mechanism beyond glucose: inhibit cardiac Na⁺/H⁺ exchanger (NHE), reduce preload/afterload

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🟡 CASE 7 — Type 1 DM (Young Patient, New Diagnosis)

INSULIN — always and only for T1DM.

• "Without functional β-cells, those with type 1 diabetes can neither maintain basal secretion of insulin nor release a bolus of insulin in response to glucose" — Lippincott Pharmacology, p. 796
• Oral agents do NOT work — there are no β-cells left to stimulate

• Check glucose before each meal and at bedtime
• Adjust bolus dose based on carbohydrate intake (carb-counting)
• Signs/symptoms of hypoglycemia (glucose < 70 mg/dL): shakiness, sweating, confusion → 15g fast sugar + recheck in 15 min

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🔴 CASE 8 — Diabetic Ketoacidosis (DKA) Emergency

Step 1: IV Fluids (fix dehydration first)

• 0.9% Normal Saline 1–2 L over first hour (10–20 mL/kg/hr)
• Switch to 0.45% saline after hemodynamic stability
• When glucose reaches 250 mg/dL → switch to Dextrose 5% + 0.45% saline to prevent hypoglycemia while continuing insulin

Step 2: Insulin Drip

• Regular insulin 0.1 units/kg IV bolus → then 0.1 units/kg/hour infusion
• DO NOT give insulin if K⁺ < 3.3 mEq/L — fix potassium first or you'll cause fatal arrhythmia
• "If the initial serum potassium is < 3.3 mmol/L, do not administer insulin until the potassium is corrected" — Harrison's, p. 3261

Step 3: Potassium Replacement

• Even though K⁺ appears high now (5.8), it will drop rapidly once insulin is started
• Add KCl to IV fluids once K⁺ < 5.0 and urine output confirmed
• Target K⁺: 4.0–5.0 mEq/L

Step 4: Find the Cause

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🔴 CASE 9 — T2DM in Pregnancy (Gestational / Pre-existing)

Switch to or add Insulin — it is the safest and most effective option in pregnancy.

• Sulfonylureas cross the placenta → risk of neonatal hypoglycemia
• "Insulin is the drug of choice for diabetes mellitus types 1 and 2 in pregnancy and gestational diabetes" — Rosen's Emergency Medicine

• Basal: NPH insulin twice daily (or Detemir — has pregnancy data)
• Bolus: Regular human insulin or rapid-acting (Aspart is approved in pregnancy) before meals

• Fasting: < 95 mg/dL
• 1-hour post-meal: < 140 mg/dL
• 2-hour post-meal: < 120 mg/dL

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🔴 CASE 10 — Advanced: T2DM with Multiple Comorbidities (Optimizing the Full Regimen)

• HbA1c: 9.8% despite Metformin + Glipizide
• eGFR: 38 (CKD stage 3b)
• EF 40% (mild heart failure)
• Recent MI 6 months ago
• BMI: 31
• Recurrent hypoglycemic episodes (because of sulfonylurea)

Problem 1: Sulfonylurea is causing hypoglycemia at his age → STOP Glipizide

• Elderly + CKD = high hypoglycemia risk with sulfonylureas
• His HbA1c target should be < 8% (not < 7%) given his age, comorbidities

Problem 2: Heart failure + post-MI → needs SGLT2 inhibitor

• Start Empagliflozin 10 mg/day — proven to reduce HF hospitalization and CV mortality
• With eGFR 38, glucose-lowering effect is reduced, but cardiac/renal benefit is still present

Problem 3: CKD with albuminuria → needs kidney protection

• Empagliflozin covers this too (dual benefit)
• Ensure he is already on an ACE inhibitor/ARB

Problem 4: HbA1c still 9.8% after removing sulfonylurea and adding SGLT2i

• Add Basal Insulin (Glargine 10 units at bedtime)
• Titrate by 2 units every 3 days until fasting glucose is 80–130 mg/dL
• "The addition of basal insulin to oral agents... allows the oral agent to provide postprandial glycemic control while the basal insulin normalizes fasting glucose" — Goodman & Gilman's, p. 1061

Final Regimen for Khalid:

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Summary: The Cheat Sheet

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