A 52-year-old man with diabetes mellitus type 2 and hypertension presents with acute kidney injury (AKI) stage 2 following contrast-enhanced coronary angiography. Serum creatinine has risen from 1.2 mg/dL to 2.8 mg/dL within 48 hours. He is euvolemic on clinical examination. What is the drug of choice to prevent progression of contrast-induced nephropathy in this patient?

Explanation

## Contrast-Induced Nephropathy (CIN) Prevention **Key Point:** Isotonic saline (0.9% NaCl) is the gold standard for prevention and management of contrast-induced acute kidney injury. It is the only intervention with consistent evidence of benefit across multiple randomized controlled trials. ### Mechanism of Protection Isotonic saline works by: 1. Expanding intravascular volume and maintaining renal perfusion pressure 2. Reducing renal vasoconstriction induced by contrast agents 3. Diluting contrast concentration in the renal tubules 4. Promoting osmotic diuresis and rapid tubular clearance of contrast ### Dosing Protocol - **Pre-procedure:** 1 mL/kg/hour for 6 hours before contrast administration - **During procedure:** Continue at same rate - **Post-procedure:** Continue for 6 hours after procedure - **Total volume:** Typically 1–1.5 L depending on body weight and cardiac status ### Evidence Base **High-Yield:** Multiple meta-analyses confirm that hydration with isotonic saline reduces CIN incidence from ~15% to ~5% in high-risk patients (diabetes, chronic kidney disease, advanced age, dehydration). **Clinical Pearl:** The benefit of saline is independent of the type of contrast used (ionic vs. non-ionic, high-osmolar vs. low-osmolar). Adequate hydration is the cornerstone of CIN prevention. ### Comparison with Other Agents | Agent | Evidence | Current Role | |-------|----------|-------------| | **Isotonic saline** | Strong, consistent benefit | **Gold standard** | | N-acetylcysteine | Mixed/weak evidence | Adjunctive, not first-line | | Sodium bicarbonate | No superiority over saline | Not recommended | | Mannitol | Increases contrast concentration | Contraindicated | | Theophylline | Weak evidence | Not recommended | **Warning:** Avoid loop diuretics and osmotic agents (mannitol, furosemide) as they worsen dehydration and increase CIN risk. ### Additional Preventive Measures 1. **Minimize contrast volume:** Use the ratio of contrast volume to eGFR; keep <3.7 if possible 2. **Delay elective procedures:** If eGFR <30, consider delaying non-urgent angiography 3. **Withhold nephrotoxic drugs:** Metformin (if eGFR <30), ACE-I/ARB (controversial, often held), NSAIDs 4. **Optimize hydration status:** Assess volume status carefully; avoid both hypovolemia and pulmonary edema **Mnemonic:** HYDRATE — **H**ypervolemia prevention, **Y**olume expansion with isotonic saline, **D**elay if possible, **R**educe contrast load, **A**void nephrotoxins, **T**herapy continuation post-procedure, **E**GFR-based risk stratification.