Management of Impaired Renal Function (eGFR 67 mL/min/1.73m²)
This patient has Stage 2-3a chronic kidney disease (CKD) and requires immediate medication review, nephrotoxin avoidance, and regular monitoring—serum creatinine alone is insufficient for assessing renal function and dramatically underestimates impairment, particularly in elderly patients. 1
Immediate Assessment and Classification
Calculate creatinine clearance using Cockcroft-Gault formula rather than relying on serum creatinine alone, as creatinine of 0.86 mg/dL may mask significant renal impairment, especially in elderly patients with decreased muscle mass 2, 1
The eGFR of 67 mL/min/1.73m² indicates Stage 2 CKD (mild reduction) if kidney damage is present, or early Stage 3a if this represents isolated GFR reduction 3
BUN:creatinine ratio of 23:1 is mildly elevated (normal <20:1), suggesting possible prerenal component or early intrinsic kidney disease 1
Critical Medication Review and Adjustments
Medications Requiring Immediate Action
Stop all NSAIDs and COX-2 inhibitors immediately—these are nephrotoxic and can precipitate acute-on-chronic kidney injury 2, 1, 4
Review and adjust all renally-cleared medications based on calculated creatinine clearance, not serum creatinine 2, 4
Discontinue metformin if eGFR falls below 45 mL/min/1.73m² (assess benefit-risk), and absolutely contraindicated if eGFR <30 mL/min/1.73m² due to lactic acidosis risk 5
Specific Drug Class Considerations
Antibiotics: Most require dose adjustment at eGFR <60 mL/min; use Cockcroft-Gault formula for dosing calculations rather than eGFR 2
Antivirals: Tenofovir, acyclovir, ganciclovir, and foscarnet all require dose reduction; maintain adequate hydration to prevent crystal nephropathy 2
Antihypertensives: ACE inhibitors/ARBs can be continued but monitor creatinine—up to 30% increase is acceptable and usually returns to baseline 3
Monitoring Protocol
Obtain complete metabolic panel, urinalysis with microscopy, and renal ultrasound to assess for structural abnormalities, proteinuria, and electrolyte disturbances 1
Monitor eGFR at least every 3-6 months in stable patients; more frequently (monthly) if on nephrotoxic agents or at risk for progression 2, 6
Check for proteinuria as this significantly increases cardiovascular and progression risk 3
Nephrotoxin Avoidance Strategy
High-Risk Medications to Avoid or Use with Extreme Caution
Aminoglycosides: Require therapeutic drug monitoring and extended-interval dosing; avoid if alternatives exist 2, 7
Contrast media: Hold metformin 48 hours before and after contrast studies; ensure adequate hydration with normal saline 5, 7
Lithium, calcineurin inhibitors: Require dose adjustment and therapeutic drug monitoring 7
Protective Measures When Nephrotoxic Drugs Are Unavoidable
Hydrate with normal saline before and after exposure to high-risk agents (contrast, aminoglycosides, cisplatin)—this is the most consistently effective prophylactic measure 7
Avoid volume depletion which dramatically increases nephrotoxicity risk 7
Monitor drug levels when available (aminoglycosides, vancomycin, lithium) 2, 7
Common Pitfalls to Avoid
Do not rely on serum creatinine alone—it underestimates renal impairment by up to 40% in elderly patients due to decreased muscle mass 2, 1, 4
Do not use standard drug dosing without calculating creatinine clearance—this leads to drug accumulation and toxicity 4, 8
Do not use thiazide diuretics as monotherapy if eGFR approaches <30 mL/min—switch to loop diuretics 3
Do not combine multiple nephrotoxins (NSAIDs + ACE inhibitors + diuretics = "triple whammy") without close monitoring 7
Specific Clinical Scenarios
For Patients Requiring Chemotherapy
Use Cockcroft-Gault formula for carboplatin dosing calculations, not MDRD, as it is more practical and validated for drug dosing 2
Consider cystatin C measurement for more accurate GFR estimation in patients receiving renally-cleared chemotherapy agents 2
Prefer agents less dependent on renal clearance within each drug class when options exist 2
For Patients with Diabetes
Metformin is safe at eGFR 67 mL/min but requires reassessment if eGFR falls below 45 mL/min/1.73m² 5
SGLT2 inhibitors lose efficacy at eGFR <45 mL/min but may still provide cardiovascular/renal protection 3
For Patients Requiring Antibiotics
Adjust fluoroquinolone dosing: Levofloxacin requires dose reduction at CrCl <50 mL/min; moxifloxacin does not 2
Extend dosing intervals for aminoglycosides and vancomycin rather than reducing individual doses to maintain peak concentrations 2
Trimethoprim-sulfamethoxazole requires dose reduction at CrCl <30 mL/min 2
When to Refer to Nephrology
Consider referral at eGFR <60 mL/min for specialized management, particularly if progressive decline or proteinuria present 3
Urgent referral required if eGFR <30 mL/min, rapidly declining function (>5 mL/min/year), or nephrotic-range proteinuria 1