What to Check Before Starting Spironolactone
Before initiating spironolactone, you must verify that serum creatinine is ≤2.5 mg/dL in men or ≤2.0 mg/dL in women (or eGFR >30 mL/min/1.73 m²) and serum potassium is <5.0 mEq/L. 1
Essential Pre-Treatment Laboratory Tests
Renal Function Assessment
- Measure serum creatinine to ensure it meets safety thresholds: <2.5 mg/dL in men or <2.0 mg/dL in women 1
- Calculate estimated glomerular filtration rate (eGFR) which must be >30 mL/min/1.73 m² 1
- In elderly patients or those with low muscle mass where creatinine may not accurately reflect kidney function, direct measurement of eGFR or creatinine clearance is recommended 1
Electrolyte Panel
- Check serum potassium - must be <5.0 mEq/L before initiation 1
- Assess baseline sodium, magnesium, and calcium as spironolactone can cause hyponatremia, hypomagnesemia, and hypocalcemia 2
- Measure serum chloride since hypochloremic alkalosis can occur 2
Additional Baseline Tests
- Blood urea nitrogen (BUN) to assess renal function 3
- Serum glucose as hyperglycemia can occur 2
- Uric acid since asymptomatic hyperuricemia is common 2
Critical Safety Considerations
Contraindications Based on Lab Values
Spironolactone is potentially harmful and contraindicated when 1:
- Serum creatinine >2.5 mg/dL in men or >2.0 mg/dL in women
- eGFR <30 mL/min/1.73 m²
- Potassium >5.0 mEq/L
Medication Review Required
Before starting spironolactone, you must 2:
- Discontinue or reduce potassium supplements - these should generally be stopped in heart failure patients 1
- Review all medications that increase potassium: ACE inhibitors, ARBs, NSAIDs, heparin, low molecular weight heparin, and trimethoprim 2
- Counsel patients to avoid potassium-containing salt substitutes and potassium-rich foods 1
- Check for concurrent nephrotoxic drugs (aminoglycosides, cisplatin, NSAIDs) that increase risk of worsening renal function 2
Post-Initiation Monitoring Protocol
Early Monitoring (Critical Period)
- Recheck potassium and renal function within 2-3 days after starting spironolactone 1
- Repeat labs again at 7 days post-initiation 1
- Monitor at 1 week and 4 weeks after starting treatment 1
Ongoing Surveillance
- Monthly monitoring for the first 3 months, then every 3 months thereafter 1
- After achieving maintenance dose: monitor at 1,2,3, and 6 months, then every 6 months 1
- More frequent monitoring is needed when spironolactone is combined with other drugs that cause hyperkalemia or in patients with impaired renal function 2
Common Pitfalls to Avoid
Risk of Hyperkalemia
The most serious risk is life-threatening hyperkalemia, which occurs more frequently in real-world practice than in clinical trials, especially in elderly patients 1. Research shows that even with low-dose spironolactone (25 mg daily), serum potassium increases significantly, though typically remains within clinically acceptable ranges with intact renal function 3.
Inadequate Baseline Assessment
Failure to verify baseline electrolytes and renal function before starting spironolactone can lead to serious adverse effects 1. Studies demonstrate that patients with advanced CKD (eGFR <45 mL/min/1.73 m²) who receive spironolactone have higher readmission rates 4, emphasizing the importance of proper patient selection.
Volume Status Evaluation
Assess for volume depletion before initiation, as excessive diuresis can cause symptomatic dehydration, hypotension, and worsening renal function, particularly in salt-depleted patients or those on ACE inhibitors/ARBs 2.