A 62-year-old woman with type 2 diabetes mellitus on metformin 1000 mg BD and hypertension on lisinopril 10 mg daily presents with a 3-day history of acute gastroenteritis with persistent vomiting and diarrhoea. Her serum creatinine has risen from 0.8 mg/dL (baseline) to 1.6 mg/dL. She is haemodynamically stable but mildly dehydrated. What is the most appropriate immediate next step?

Explanation

## Clinical Context This patient has **acute kidney injury (AKI)** secondary to dehydration from gastroenteritis. The doubled serum creatinine reflects a significant drop in glomerular filtration rate (GFR). Two drugs require immediate action: **metformin** (lactic acidosis risk in renal failure) and **ACE inhibitor** (worsening renal perfusion). ## Why Metformin Must Be Held **Key Point:** Metformin is contraindicated in renal impairment (eGFR < 30 mL/min/1.73 m²) due to accumulation and risk of **metformin-associated lactic acidosis (MALA)**. In acute renal dysfunction, metformin must be held until renal function stabilizes. | Renal Function | Metformin Action | |---|---| | eGFR ≥ 45 | Use with caution; monitor | | eGFR 30–44 | Contraindicated; hold | | eGFR < 30 | Absolutely contraindicated | **High-Yield:** MALA is rare but fatal (mortality ~50%). Risk increases with renal impairment, dehydration, sepsis, and contrast exposure. ## Why ACE Inhibitors Must Be Held **Clinical Pearl:** ACE inhibitors reduce intraglomerular pressure by dilating the efferent arteriole. In acute dehydration and AKI, they can precipitate **acute tubular necrosis** or worsen renal perfusion. Holding the ACE inhibitor allows renal autoregulation to restore GFR as volume status improves. ## Management Algorithm for Drug-Induced AKI ```mermaid flowchart TD A[Acute rise in creatinine + dehydration]:::outcome --> B{Identify nephrotoxic drugs}:::decision B -->|Metformin| C[Hold metformin]:::action B -->|ACE-I/ARB| D[Hold ACE-I/ARB]:::action B -->|NSAIDs| E[Hold NSAIDs]:::action C --> F[IV fluids to restore volume]:::action D --> F E --> F F --> G[Recheck creatinine in 48-72 hrs]:::action G --> H{Creatinine improving?}:::decision H -->|Yes| I[Restart drugs cautiously]:::action H -->|No| J[Further investigation for AKI]:::action ``` ## Next Steps in This Patient 1. **Hold metformin** (risk of MALA in AKI) 2. **Hold lisinopril** (worsens renal perfusion in dehydration) 3. **IV fluids** (0.9% saline, 500 mL bolus, then maintenance based on urine output and vital signs) 4. **Antiemetics** (ondansetron 4–8 mg IV/PO) 5. **Recheck serum creatinine and electrolytes in 48 hours** 6. **Monitor urine output** (target > 0.5 mL/kg/hr) **Warning:** Do NOT continue metformin in AKI. Do NOT use NSAIDs or contrast agents until renal function recovers. ## Reinitiation Criteria - Serum creatinine returns to baseline or near-baseline - Oral intake is adequate - No ongoing diarrhoea or vomiting - eGFR is reassessed and documented [cite:KD Tripathi 8e Ch 13; Harrison 21e Ch 297]