Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
HYDRALAZINE HYDROCHLORIDE vs GONITRO
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Vasodilation of arterioles by direct relaxation of vascular smooth muscle, likely involving interference with calcium movement.
Nitric oxide (NO) donor; activates guanylyl cyclase, increasing c GMP in vascular smooth muscle, leading to vasodilation.
Hypertension,Heart failure (adjunctive therapy)
Prevention of angina pectoris due to coronary artery disease,Acute relief of angina episodes,Prophylaxis for angina before exertion or stress
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.
Sublingual: 0.3-0.6 mg at onset of angina, may repeat every 5 minutes up to 3 doses within 15 minutes. Prophylactic: 0.3-0.6 mg 5-10 minutes before activity. Transdermal: Apply 0.2-0.8 mg/hour patch once daily, remove at bedtime to prevent tolerance. Intravenous: Start at 5 mcg/min, titrate by 5-20 mcg/min every 3-5 minutes based on hemodynamic response; usual range 10-200 mcg/min.
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.
Terminal elimination half-life approximately 2-3 minutes for nitroglycerin; clinical effects cease within 30-60 minutes due to rapid redistribution and metabolism
Extensively metabolized in the liver via N-acetylation (N-acetyltransferase 2, NAT2) and subsequent conjugation; also metabolized by cytochrome P450 (CYP) enzymes.
Extensively metabolized by mitochondrial aldehyde dehydrogenase (ALDH2) in vascular smooth muscle; also metabolized by glutathione S-transferases and cytochrome P450 (CYP3A4).
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.
Primarily renal: 80-90% as inactive metabolites (dinitrates, mononitrates); minor biliary/fecal (<10%)
Approximately 85–90% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
60% bound, primarily to plasma albumin
1.5–1.8 L/kg. This large Vd indicates extensive distribution into tissues, including arteriolar smooth muscle.
Approximately 3.3 L/kg; extensive tissue distribution with high affinity for vascular smooth muscle
Oral bioavailability is about 26–50% due to significant first-pass metabolism. Bioavailability is higher in slow acetylators compared to rapid acetylators.
Sublingual: 40-60%; Oral (immediate-release): <10% due to first-pass hepatic metabolism; Transdermal: 70-90% (drug-in-adhesive); Intravenous: 100%
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.
No specific dose adjustment required for renal impairment. However, use with caution in severe renal dysfunction (Cr Cl <30 m L/min) due to increased risk of hypotension and methemoglobinemia.
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.
Child-Pugh A: No adjustment needed. Child-Pugh B: Reduce dose by 50% due to decreased clearance. Child-Pugh C: Avoid use or use with extreme caution; consider alternative therapy.
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).
Sublingual: 5-10 mcg/kg/dose, maximum 0.3 mg per dose, may repeat every 5 minutes up to 3 doses. Intravenous: Start at 0.25-0.5 mcg/kg/min, titrate up to 1-5 mcg/kg/min based on response. Not recommended for children <1 year due to limited data.
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.
Initiate at lower doses due to increased sensitivity: Sublingual: 0.15-0.3 mg; Transdermal: 0.2 mg/day patch; Intravenous: Start at 5 mcg/min, titrate slowly. Monitor for hypotension and syncope. Avoid sustained-release formulations due to prolonged half-life.
May cause a syndrome resembling systemic lupus erythematosus (SLE), especially with prolonged use or high doses.
Do not use with phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil) due to risk of severe hypotension.
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.
Hypotension (especially with volume depletion or diuretic therapy), reflex tachycardia, tolerance (intermittent dosing with nitrate-free interval recommended), abrupt discontinuation may cause angina rebound.
Hypersensitivity to hydralazine, mitral valvular rheumatic heart disease, coronary artery disease, and idiopathic systemic lupus erythematosus.
Concomitant use with PDE-5 inhibitors (sildenafil, tadalafil, vardenafil), severe anemia, increased intracranial pressure, hypersensitivity to nitrates, acute myocardial infarction with low filling pressure.
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.
Avoid alcohol consumption as it may exacerbate nitroglycerin-induced hypotension and vasodilation. No specific food interactions documented; however, patients should maintain adequate hydration. High-fat meals may delay absorption, but sublingual route minimizes this effect. Grapefruit juice has no known interaction.
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.
FDA Pregnancy Category C. First trimester: no increased risk of major malformations in human studies; animal studies show fetal toxicity at high doses. Second/third trimesters: risk of fetal bradycardia, hypotension, and reduced uteroplacental perfusion; avoid near term due to risk of maternal hypotension and neonatal bradycardia.
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.
Not recommended during breastfeeding. No data on M/P ratio; minimal excretion into breast milk expected but safety not established. Potential for infant hypotension and bradycardia.
Increased clearance in pregnancy may require higher doses to achieve same antihypertensive effect; start low and titrate based on blood pressure response.
No standard dose adjustment required for pregnancy; use lowest effective dose. Increased plasma volume may reduce response; titrate to effect. Avoid in severe preeclampsia or volume depletion.
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.
GONITRO (nitroglycerin sublingual powder) is indicated for acute relief of angina pectoris. Administer one packet (0.4 mg or 0.8 mg) at onset of chest pain; may repeat every 5 minutes up to 3 doses. Ensure patient is seated or lying down to avoid hypotension. Do not confuse with oral spray; powder must be placed under tongue. Onset within 1-3 minutes. Common side effect: headache. Contraindicated with phosphodiesterase-5 inhibitors (e.g., sildenafil) within 24-48 hours due to severe hypotension. Monitor for orthostatic hypotension.
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.
Take one packet at the first sign of chest pain. Empty the entire powder under your tongue and let it dissolve. Do not swallow or rinse with water.,If pain persists after 5 minutes, take a second packet. If still no relief after 5 more minutes, take a third and call 911.,Sit or lie down when taking this medication to prevent dizziness or fainting.,Avoid alcohol; it may worsen side effects like low blood pressure.,Do not use Viagra, Cialis, Levitra, or other erectile dysfunction drugs while on this medicine—serious drop in blood pressure can occur.,Headaches are common; do not stop taking the medication. Over-the-counter pain relievers may help.,Store packets at room temperature away from moisture and heat. Do not open until ready to use.
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about HYDRALAZINE HYDROCHLORIDE vs GONITRO, answered by our medical review team.
HYDRALAZINE HYDROCHLORIDE is a Vasodilator that works by Vasodilation of arterioles by direct relaxation of vascular smooth muscle, likely involving interference with calcium movement.. GONITRO is a Nitrate Vasodilator that works by Nitric oxide (NO) donor; activates guanylyl cyclase, increasing c GMP in vascular smooth muscle, leading to vasodilation.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between HYDRALAZINE HYDROCHLORIDE and GONITRO 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 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.. The standard adult dose of GONITRO is: Sublingual: 0.3-0.6 mg at onset of angina, may repeat every 5 minutes up to 3 doses within 15 minutes. Prophylactic: 0.3-0.6 mg 5-10 minutes before activity. Transdermal: Apply 0.2-0.8 mg/hour patch once daily, remove at bedtime to prevent tolerance. Intravenous: Start at 5 mcg/min, titrate by 5-20 mcg/min every 3-5 minutes based on hemodynamic response; usual range 10-200 mcg/min.. 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 HYDRALAZINE HYDROCHLORIDE and GONITRO 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. 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. GONITRO is classified as Category C. FDA Pregnancy Category C. First trimester: no increased risk of major malformations in human studies; animal studies show fetal toxicity at high doses. Second/third trimesters: ris. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.