Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BIDIL vs HYDRALAZINE HYDROCHLORIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Combination of isosorbide dinitrate (a nitric oxide donor) and hydralazine (a direct vasodilator). Isosorbide dinitrate relaxes vascular smooth muscle via NO-mediated c GMP production; hydralazine reduces peripheral resistance and may inhibit DNA synthesis in endothelial cells. Synergy enhances vasodilation and improves cardiac output.
Vasodilation of arterioles by direct relaxation of vascular smooth muscle, likely involving interference with calcium movement.
Heart failure: treatment to improve survival, prolong time to hospitalization, and improve quality of life in self-identified black patients with heart failure (NYHA class III-IV) receiving standard therapy (diuretics, ACE inhibitors/ARBs, beta-blockers). Off-label: none significant.
Hypertension,Heart failure (adjunctive therapy)
Isosorbide dinitrate 20 mg plus hydralazine 37.5 mg orally three times daily; titrate to target dose of isosorbide dinitrate 40 mg plus hydralazine 75 mg three times daily as tolerated.
Oral: Initiate with 10 mg 4 times daily for 2-4 days, then increase to 25 mg 4 times daily for the remainder of the week, then titrate to 50 mg 4 times daily. Maximum daily dose: 300 mg. Intravenous: 5-20 mg IV bolus, may repeat every 20-30 minutes as needed, or continuous IV infusion 0.5-10 mg/hour.
Hydralazine: 2-4 hours (fast acetylators), 4-8 hours (slow acetylators); isosorbide dinitrate: 1 hour (parent), 4-5 hours (isosorbide-5-mononitrate, active metabolite). Clinical context: Requires twice-daily dosing for sustained effect.
The terminal elimination half-life of hydralazine is approximately 2–4 hours in patients with normal renal function, but it is prolonged in renal impairment (up to 7–16 hours). The antihypertensive effect often lasts longer than the half-life due to persistent binding to arteriolar receptors.
Isosorbide dinitrate: extensively metabolized by denitration and conjugation in the liver; hydralazine: primarily metabolized by N-acetylation (N-acetyltransferase 2, NAT2) and subsequent glucuronidation.
Extensively metabolized in the liver via N-acetylation (N-acetyltransferase 2, NAT2) and subsequent conjugation; also metabolized by cytochrome P450 (CYP) enzymes.
Hydralazine: 80% renal (as active drug and metabolites, predominantly N-acetylhydralazine and hydralazine pyruvic acid hydrazone); isosorbide dinitrate: renal (metabolites, primarily isosorbide mononitrates and isosorbide) and fecal (minor).
Hydralazine is primarily metabolized in the liver via N-acetylation (polymorphic) and hydroxylation. Less than 10% of the dose is excreted unchanged in urine. The major metabolites are hydralazine pyruvic acid hydrazone and other conjugates, which are excreted renally. Fecal elimination is negligible.
Hydralazine: 87-90% (plasma proteins); isosorbide dinitrate: 30-40% (albumin).
Approximately 85–90% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Hydralazine: 1.6 L/kg; isosorbide dinitrate: 2-4 L/kg. Clinical meaning: Extensive tissue distribution for both components.
1.5–1.8 L/kg. This large Vd indicates extensive distribution into tissues, including arteriolar smooth muscle.
Hydralazine: 30-50% (oral, first-pass effect); isosorbide dinitrate: 20-30% (oral, extensive first-pass metabolism).
Oral bioavailability is about 26–50% due to significant first-pass metabolism. Bioavailability is higher in slow acetylators compared to rapid acetylators.
No specific dose adjustment recommended; however, hydralazine is cleared renally and may accumulate in severe renal impairment (Cr Cl <30 m L/min); consider monitoring for adverse effects.
Cr Cl 10-50 m L/min: Administer every 8 hours. Cr Cl <10 m L/min: Administer every 8-16 hours. Dose reduction may be necessary to avoid accumulation.
Contraindicated in severe hepatic impairment (Child-Pugh class C). In mild to moderate impairment (Child-Pugh A or B), no specific dose adjustment but caution advised due to potential increased exposure.
Child-Pugh Class A and B: No specific recommendations; use with caution. Child-Pugh Class C: Contraindicated due to risk of hepatotoxicity and reduced drug clearance.
Safety and efficacy not established in pediatric patients; no standard dosing recommendations available.
Oral: 0.75-1 mg/kg/day divided every 6-12 hours, maximum 5 mg/kg/day. Intravenous: 0.1-0.2 mg/kg/dose IV every 4-6 hours as needed, maximum 0.5 mg/kg/dose (20 mg).
Initiate at lower end of dosing range; titrate slowly due to increased risk of hypotension and dizziness; monitor renal function as hydralazine clearance may decrease.
Initiate at lower doses (e.g., 10 mg 2-3 times daily) and titrate slowly due to increased risk of hypotension and drug accumulation; monitor renal function closely.
None.
May cause a syndrome resembling systemic lupus erythematosus (SLE), especially with prolonged use or high doses.
Hypotension (monitor blood pressure), agranulocytosis (rare; hydralazine may cause neutropenia; monitor CBC), drug-induced lupus-like syndrome (hydralazine; discontinue if symptoms develop), hepatotoxicity (hydralazine; monitor liver enzymes), risk of syncope when initiating or increasing dose, volume depletion (correct before use).
May cause drug-induced lupus, peripheral neuritis (pyridoxine deficiency), myocardial infarction (precipitate angina), hypotension, tachycardia, and blood dyscrasias. Use with caution in patients with coronary artery disease, cerebrovascular disease, or renal impairment.
Hypersensitivity to hydralazine or isosorbide dinitrate, severe hypotension (<100 mm Hg systolic), acute myocardial infarction (safety not established), cardiogenic shock, cardiomyopathy with restrictive/obstructive physiology, use with phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil) due to risk of severe hypotension.
Hypersensitivity to hydralazine, mitral valvular rheumatic heart disease, coronary artery disease, and idiopathic systemic lupus erythematosus.
No specific food interactions. Avoid excessive alcohol intake as it may exacerbate hypotension.
Hydralazine absorption is significantly increased when taken with food; it is recommended to take with meals for consistent effect. Avoid high-tyramine foods (aged cheeses, cured meats, fermented products) if combined with MAOIs, though hydralazine itself is not an MAOI. No specific dietary restrictions otherwise.
FDA Pregnancy Category C. First trimester: Animal studies show fetal harm; no adequate human studies. Second and third trimesters: Hydralazine crosses placenta; may cause fetal hypotension, thrombocytopenia. Isosorbide dinitrate: Limited data; associated with methemoglobinemia in neonates. Use only if benefit outweighs risk.
First trimester: Limited human data; animal studies show no teratogenicity. Second/third trimester: Associated with maternal hypotension and potential fetal distress; no known structural anomalies.
Hydralazine is excreted in breast milk (M/P ratio ~1.2); low levels unlikely to harm infant. Isosorbide dinitrate: No data on excretion. Monitor infant for hypotension. American Academy of Pediatrics considers hydralazine compatible with breastfeeding.
Hydralazine is excreted into breast milk in small amounts (M/P ratio ~0.8). Considered compatible with breastfeeding by AAP; monitor infant for hypotension or drowsiness.
Pregnancy may increase volume of distribution and clearance of hydralazine; dose adjustments may be needed to maintain efficacy. Isosorbide dinitrate: no specific recommendations; start at lowest effective dose and titrate based on blood pressure response. Monitor for orthostatic hypotension.
Increased clearance in pregnancy may require higher doses to achieve same antihypertensive effect; start low and titrate based on blood pressure response.
Bidil is a fixed-dose combination of isosorbide dinitrate (20 mg) and hydralazine (37.5 mg), indicated as an adjunct to standard therapy for heart failure in self-identified African American patients (NYHA class III-IV, left ventricular ejection fraction <45%). Dizziness and headache are common due to vasodilation; titrate slowly. Avoid use with phosphodiesterase-5 inhibitors (e.g., sildenafil) due to risk of severe hypotension. Monitor for fluid retention and worsening heart failure. Consider dose reduction in hepatic impairment.
Hydralazine is a direct-acting arterial vasodilator; its antihypertensive effect is limited by reflex tachycardia and fluid retention, so it is typically used in combination with a beta-blocker and a diuretic. Slow acetylators are at increased risk of drug-induced lupus, especially with doses >200 mg/day. Administer with food to enhance bioavailability; onset of action occurs within 20-30 minutes IV. For hypertensive urgency, IV hydralazine 5-20 mg every 20-30 min is used, but avoid in suspected myocardial ischemia due to reflex tachycardia.
Take this medication exactly as prescribed, usually three times daily with or without food.,Do not take with erectile dysfunction drugs (e.g., Viagra, Cialis, Levitra) as this can cause a dangerous drop in blood pressure.,Common side effects include dizziness and headache, which may improve over time; report severe or persistent symptoms to your doctor.,Avoid sudden position changes to prevent falls.,Do not stop taking this medication abruptly without consulting your healthcare provider.,Inform all healthcare providers you are taking Bidil.,Store at room temperature, away from moisture and heat.
Take exactly as prescribed, with food or milk to increase absorption.,Do not stop abruptly; sudden cessation can cause severe rebound hypertension.,Report symptoms like chest pain, rapid heartbeat, joint pain, rash, or fever to your doctor.,Avoid alcohol and other antihypertensives unless approved by your doctor.,Inform your doctor if you become pregnant or plan to become pregnant.,May cause dizziness; rise slowly from sitting or lying down.
No interactions on record
"Oxaprozin, a nonsteroidal anti-inflammatory drug (NSAID), can reduce the antihypertensive efficacy of hydralazine, a direct-acting vasodilator. NSAIDs inhibit prostaglandin synthesis, which can lead to sodium and fluid retention and increased vascular resistance, thereby counteracting the vasodilatory effects of hydralazine. This interaction may result in diminished blood pressure control and require dosage adjustments or alternative therapies."
"Hydralazine, a direct-acting vasodilator, may reduce the antihypertensive efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) like sulindac. NSAIDs inhibit cyclooxygenase-mediated prostaglandin synthesis, leading to sodium retention and increased vascular tone, which can antagonize the vasodilatory effects of hydralazine. This interaction may result in elevated blood pressure and diminished control of hypertension in patients receiving both agents."
"Hydralazine, a direct-acting vasodilator, may reduce the antihypertensive efficacy of Tolfenamic acid, a nonsteroidal anti-inflammatory drug (NSAID) that non-selectively inhibits cyclooxygenase (COX) enzymes. The interaction arises because Tolfenamic acid's inhibition of COX-2 reduces synthesis of vasodilatory prostaglandins (e.g., prostacyclin) in the vascular endothelium, which counteracts the vasodilation induced by Hydralazine. Clinically, this can lead to blunted blood pressure reduction, potentially requiring dose adjustments or alternative therapies to maintain adequate hypertension control."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about BIDIL vs HYDRALAZINE HYDROCHLORIDE, answered by our medical review team.
BIDIL is a Vasodilator Combination that works by Combination of isosorbide dinitrate (a nitric oxide donor) and hydralazine (a direct vasodilator). Isosorbide dinitrate relaxes vascular smooth muscle via NO-mediated c GMP production; hydralazine reduces peripheral resistance and may inhibit DNA synthesis in endothelial cells. Synergy enhances vasodilation and improves cardiac output.. HYDRALAZINE HYDROCHLORIDE is a Vasodilator that works by Vasodilation of arterioles by direct relaxation of vascular smooth muscle, likely involving interference with calcium movement.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between BIDIL and HYDRALAZINE HYDROCHLORIDE depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of BIDIL is: Isosorbide dinitrate 20 mg plus hydralazine 37.5 mg orally three times daily; titrate to target dose of isosorbide dinitrate 40 mg plus hydralazine 75 mg three times daily as tolerated.. The standard adult dose of HYDRALAZINE HYDROCHLORIDE is: Oral: Initiate with 10 mg 4 times daily for 2-4 days, then increase to 25 mg 4 times daily for the remainder of the week, then titrate to 50 mg 4 times daily. Maximum daily dose: 300 mg. Intravenous: 5-20 mg IV bolus, may repeat every 20-30 minutes as needed, or continuous IV infusion 0.5-10 mg/hour.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between BIDIL and HYDRALAZINE HYDROCHLORIDE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. BIDIL is classified as Category C. FDA Pregnancy Category C. First trimester: Animal studies show fetal harm; no adequate human studies. Second and third trimesters: Hydralazine crosses placenta; may cause fetal hyp. HYDRALAZINE HYDROCHLORIDE is classified as Category A/B. First trimester: Limited human data; animal studies show no teratogenicity. Second/third trimester: Associated with maternal hypotension and potential fetal distress; no known stru. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.