Hydralazine-Isosorbide Dinitrate for Heart Failure with Reduced Ejection Fraction
Add hydralazine-isosorbide dinitrate (Hy-ISDN) to standard therapy in self-identified Black patients with NYHA class III-IV HFrEF who remain symptomatic despite optimal medical therapy with ACEi/ARB (or ARNi), beta-blockers, and mineralocorticoid receptor antagonists. 1
Primary Indication: Self-Identified Black Patients
The 2022 ACC/AHA/HFSA guidelines provide a Class 1A recommendation for adding Hy-ISDN in Black patients with advanced symptomatic HFrEF already on guideline-directed medical therapy 1. This is based on the landmark A-HeFT trial, which demonstrated a 43% reduction in all-cause mortality (10.2% vs 6.2%, P=0.02), a 33% reduction in first HF hospitalization, and improved quality of life when this combination was added to standard therapy 2. The trial was terminated early due to the remarkable mortality benefit 1.
Key Points for Black Patients:
- Must be on background therapy with ACEi/ARB, beta-blockers, and MRA
- NYHA class III-IV symptoms despite optimal therapy
- Insufficient data exist for concomitant use with ARNi 1
- The benefit was seen only at the higher doses used in trials (target: isosorbide dinitrate 40 mg three times daily + hydralazine 75 mg three times daily) 3
Secondary Indication: Intolerance to First-Line Agents
Consider Hy-ISDN (Class 2b, C-LD recommendation) in patients who cannot tolerate ACEi, ARB, or ARNi due to drug intolerance or renal insufficiency 1. This is a weaker recommendation with lower-quality evidence, and referral to a heart failure specialist is advisable for these complex cases 1.
Dosing Algorithm
Start with isosorbide dinitrate 20 mg three times daily + hydralazine 25 mg three times daily (or fixed-dose combination 1 tablet three times daily) 3.
Titrate to target doses:
- Isosorbide dinitrate: 40 mg three times daily
- Hydralazine: 75 mg three times daily
- Fixed-dose combination: 2 tablets three times daily 3
Critical Dosing Considerations:
You must provide a daily dose-free interval of at least 14 hours to prevent nitrate tolerance 4. The medication provides approximately 12 hours of anti-anginal efficacy per day, so dosing should be structured to allow this nitrate-free period 4. For example, dose at 8 AM, 1 PM, and 6 PM, leaving overnight as the dose-free interval.
The benefits in clinical trials were achieved only with these higher target doses—lower doses typically used in clinical practice have not shown the same mortality benefit 1. However, uptake remains modest due to the complexity of the three-times-daily regimen and adverse effects, with very low prescription refill rates even when prescribed 1.
Contraindications and Warnings
Absolute contraindications 4:
- Concurrent use of phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil) - can cause severe hypotension, syncope, or myocardial ischemia
- Concurrent use of riociguat (soluble guanylate cyclase stimulator)
- Allergy to isosorbide dinitrate or hydralazine
Important warnings 4:
- Not recommended in acute myocardial infarction or acute decompensated heart failure due to difficulty terminating effects rapidly
- Requires careful hemodynamic monitoring to avoid hypotension and tachycardia
- Treat severe hypotension with extremity elevation and central volume expansion 4
Common Pitfalls
Underdosing: The mortality benefit requires target doses (isosorbide dinitrate 40 mg TID + hydralazine 75 mg TID). Lower doses have not demonstrated the same outcomes 1.
Forgetting the dose-free interval: Continuous 24-hour nitrate exposure causes refractory tolerance, negating benefits 4.
Poor adherence: The three-times-daily regimen has notoriously low refill rates. Consider the fixed-dose combination to simplify the regimen 1.
Underuse in eligible populations: Despite strong evidence, this therapy is dramatically underutilized, particularly in Europe, potentially resulting in thousands of excess deaths annually 5.
Using with ARNi without evidence: There are insufficient data to guide concomitant use with sacubitril-valsartan 1.
Evidence Quality and Nuances
The A-HeFT trial provides robust evidence for Black patients, though the result is somewhat vulnerable to the small number of events and early trial termination 1. The biological mechanism may relate to absence of European ancestry rather than race per se, with ongoing research focused on genetic determinants of response 6, 7.
The combination produces left ventricular reverse remodeling even when added to neurohormonal inhibitors, with increases in ejection fraction (2.8% vs 0.8%), decreases in LV mass index, and reductions in BNP levels 8. These mechanistic benefits—including arterial and venous vasodilation, antioxidant effects, improved NO bioavailability, and mitigation of nitrate tolerance—explain the mortality reduction 9.
For non-Black patients or those intolerant to ACEi/ARB/ARNi, the evidence is weaker (based on older V-HeFT trials without modern background therapy), making specialist consultation advisable 1.