Dosing and Titration of Hydralazine-Isosorbide Dinitrate (H-ISDN) in Systolic Heart Failure
Start with the fixed-dose combination at 20 mg isosorbide dinitrate/37.5 mg hydralazine three times daily, then titrate over 3 weeks to the target dose of 40 mg isosorbide dinitrate/75 mg hydralazine three times daily (total daily: 120 mg/225 mg). 1
Initial Dosing Strategy
Begin with one tablet of the fixed-dose combination (20 mg ISDN/37.5 mg hydralazine) three times daily. This starting dose is well-tolerated and allows assessment of patient response before escalation 1.
Titration Schedule
Escalate over 3 weeks to the target dose:
- Week 1: 20 mg ISDN/37.5 mg hydralazine TID
- Week 2-3: Increase to 40 mg ISDN/75 mg hydralazine TID (target dose)
The target dose of 40 mg ISDN/75 mg hydralazine three times daily was the dose used in the pivotal A-HeFT trial that demonstrated mortality benefit 1, 2. This is critical because benefit was only demonstrated at the higher doses achieved in clinical trials, not at the lower doses typically used in practice 1.
Critical Dosing Considerations
Why Target Doses Matter
The 2022 AHA/ACC/HFSA guidelines explicitly emphasize that "the benefit in both trials was seen only at doses achieved in those trials that are higher than doses typically used in clinical practice" 1. The mean doses achieved in A-HeFT were 90 mg ISDN and 175 mg hydralazine total daily 1, which translates to approximately 30 mg/58 mg three times daily—still below the protocol target but substantially higher than typical practice patterns.
Alternative Dosing (If Fixed-Dose Not Available)
If using separate formulations: 20-30 mg ISDN with 25-50 mg hydralazine 3-4 times daily, titrating to 120 mg ISDN and 300 mg hydralazine total daily in divided doses 1.
Patient-Specific Indications
Primary Indication (Class 1 Recommendation)
Self-identified African American patients with NYHA class III-IV HFrEF who remain symptomatic despite optimal therapy with ACEi/ARB, beta-blockers, and MRA 1. This combination reduced all-cause mortality by 43% in this population 2.
Alternative Indication (Class 2b Recommendation)
Patients with HFrEF who cannot tolerate ACEi, ARB, or ARNi due to drug intolerance, hypotension, or renal insufficiency 1. However, evidence is weaker in this population, and referral to a heart failure specialist is recommended 1.
Important Caveats and Pitfalls
Insufficient Data with ARNi
There are insufficient data for concomitant use with ARNi (sacubitril-valsartan) 1. Do not assume the benefit seen with ACEi/ARB extends to ARNi combinations.
Common Barriers to Success
- Headache and gastrointestinal side effects (nausea, diarrhea) are significantly more common than placebo 3
- Uptake has been modest due to complexity of the three-times-daily regimen and adverse effects 1
- Prescription refill rates are very low, indicating poor real-world adherence 1
- Dose reductions may be necessary in some patients, but attempt to reach target doses whenever possible 3
Monitoring During Titration
- Monitor blood pressure at each dose escalation
- Intradialytic hypotension may actually decrease with H-ISDN (contrary to expectations) 3
- Assess for headache (common, often improves with continued use) and gastrointestinal symptoms
- Do not confuse with norepinephrine (NORAD IV formulation) which has completely different dosing 4
Nitrate Tolerance Concerns
The combination with hydralazine helps prevent nitrate tolerance through antioxidant effects and preservation of NO bioavailability 5, 6. The three-times-daily dosing provides some nitrate-free interval overnight, though this is shorter than ideal for tolerance prevention 7.
Economic Value
At target doses, H-ISDN provides high economic value with cost per life-year <$60,000 in African Americans with advanced HFrEF on optimal background therapy 1.