For a patient with an ejection fraction of 45–50%, should spironolactone or dapagliflozin (Farxiga) be started first?

Dapagliflozin (Farxiga) Takes Clear Precedence Over Spironolactone for EF 45-50%

For a patient with an ejection fraction of 45-50%, dapagliflozin (Farxiga) should be initiated first, as it has stronger, more recent evidence for reducing heart failure hospitalizations and cardiovascular mortality in this specific population. 1

Evidence-Based Rationale

Why SGLT2 Inhibitors Come First

The 2025 Canadian Cardiovascular Society guidelines explicitly position SGLT2 inhibitors (dapagliflozin or empagliflozin) as Tier 1 therapy for heart failure with nonreduced ejection fraction (HFnrEF), which includes your patient's EF of 45-50% 1. This represents the most current guideline recommendation available.

The DELIVER trial specifically demonstrated that dapagliflozin reduced the primary composite outcome (cardiovascular death, heart failure hospitalization, or urgent heart failure visit) by 18% in patients with LVEF >40% (HR 0.82,95% CI 0.73-0.92, P<0.001) 2. Critically, this benefit was consistent across the entire EF spectrum, including patients with EF 45-50%.

Why Spironolactone is Secondary

While the 2022 AHA/ACC/HFSA guidelines mention that mineralocorticoid receptor antagonists (MRAs) "may be considered" for HFmrEF (EF 41-49%), this is a Class 2b recommendation (weaker evidence) 3. The evidence comes primarily from post-hoc analyses rather than prospective trials designed for this population.

The TOPCAT trial failed to show a significant reduction in its primary endpoint (cardiovascular death, heart failure hospitalization, or aborted cardiac arrest) in patients with EF ≥45% (HR 0.89,95% CI 0.77-1.04, P=0.14) 4. Only heart failure hospitalizations showed benefit (HR 0.83, P=0.04), and this was driven primarily by patients at the lower end of the EF spectrum.

A post-hoc analysis of TOPCAT showed that spironolactone's benefit was greatest in patients with EF <50%, with diminishing effects as EF increased 5. For your patient at EF 45-50%, they sit at the threshold where spironolactone benefit becomes less certain.

Practical Implementation Algorithm

Step 1: Start Dapagliflozin First

• Dose: 10 mg once daily 1
• No titration needed - this is both the starting and target dose
• Check baseline eGFR: Can be used down to eGFR 25 mL/min/1.73 m² 6
• Monitor for: Volume depletion, hypotension (especially if age ≥65), genital mycotic infections

Step 2: Consider Adding Spironolactone After SGLT2i is Established

• Wait 2-4 weeks after starting dapagliflozin to assess tolerance
• Starting dose: 12.5-25 mg daily 1
• Target dose: 25-50 mg daily
• Mandatory monitoring: Potassium and creatinine at 1 week, then at 4 weeks, then every 3-4 months
• Contraindications: K+ >5.0 mEq/L, eGFR <30 mL/min/1.73 m²

Step 3: Additional GDMT Considerations

The 2025 Canadian guidelines position therapy in tiers, with no specific sequence required within a tier 1. However, based on strength of evidence:

• Tier 1: SGLT2 inhibitors (strongest evidence)
• Tier 2: Consider ARNI (sacubitril-valsartan) if hypertensive or symptomatic
• Tier 3: MRAs like spironolactone, particularly if hypertension is poorly controlled 3

Critical Caveats and Common Pitfalls

Don't Discontinue SGLT2i for Early eGFR Dips

• Acute eGFR decreases of ≥15% occur in ~20% of patients within 4 weeks 7
• This is hemodynamic, not nephrotoxic
• Continue therapy unless eGFR drops below 25 mL/min/1.73 m² or patient becomes hemodynamically unstable
• The long-term renal protection outweighs transient decreases

Spironolactone-Specific Warnings

• Hyperkalemia risk doubles (18.7% vs 9.1% with placebo) 4
• More aggressive monitoring needed if combining with ACE inhibitors, ARBs, or NSAIDs
• Consider eplerenone as alternative if gynecomastia develops (though recent data suggests eplerenone may have mortality benefit over spironolactone) 8

Patient-Specific Factors That Strengthen Spironolactone's Role

• Uncontrolled hypertension: Spironolactone has established BP-lowering effects 3
• EF closer to 45%: Greater benefit at lower end of EF spectrum 5
• Prior heart failure hospitalization: Post-hoc data suggests better response 9

Why This Hierarchy Matters for Outcomes

SGLT2 inhibitors provide benefits beyond heart failure: renal protection, reduced cardiovascular death, and metabolic advantages 1. The DELIVER trial showed consistent benefit regardless of diabetes status, making dapagliflozin universally applicable to your patient population 2.

Spironolactone's evidence in this EF range is equivocal at best, with the primary TOPCAT trial missing its primary endpoint and benefits concentrated in subgroups 4. The 2022 AHA/ACC guidelines acknowledge this uncertainty by stating "future prospective studies are needed to further clarify treatment recommendations" for HFmrEF 3.

The 2025 Canadian guidelines represent the most current expert consensus, explicitly prioritizing SGLT2 inhibitors as first-line therapy for this population 1. This reflects the evolution of evidence since the 2022 AHA/ACC guidelines were published.