Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FLOLAN vs Hydralazine
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Epoprostenol is a prostaglandin I2 (prostacyclin) analogue that directly vasodilates pulmonary and systemic arterial beds, inhibits platelet aggregation, and has antiproliferative effects on vascular smooth muscle.
Hydralazine is a direct-acting vasodilator that relaxes arteriolar smooth muscle, leading to decreased peripheral vascular resistance and blood pressure. Its exact mechanism is unclear but may involve interference with calcium movement and increased c GMP levels.
Pulmonary arterial hypertension (PAH) (WHO Group I) in NYHA Class III-IV patients to improve exercise capacity and hemodynamics,Pulmonary arterial hypertension in patients who require chronic IV therapy,Off-label: Severe Raynaud's phenomenon, primary pulmonary hypertension in neonates, and as a bridge to lung transplantation
Hypertension (adjunctive therapy),Off-label: Chronic heart failure (in combination with isosorbide dinitrate, especially in African American patients)
Initial: 4 ng/kg/min via continuous IV infusion, then titrated in increments of 1-2 ng/kg/min at intervals of at least 15 minutes based on clinical response. Typical maintenance dose: 20-40 ng/kg/min; range: 10-80 ng/kg/min.
10-50 mg orally every 6 hours, titrate to maximum 300 mg/day; 10-20 mg intramuscularly or intravenously every 4-6 hours as needed.
3–5 minutes (terminal elimination half-life; rapid inactivation necessitates continuous IV infusion).
The terminal elimination half-life of hydralazine is approximately 2-4 hours in patients with normal renal function. However, the duration of antihypertensive effect may be longer (6-12 hours) due to tissue binding and slow release from vascular smooth muscle. In renal impairment, half-life may extend to 7-16 hours, necessitating dose adjustment.
Epoprostenol undergoes rapid hydrolysis at neutral p H and is also metabolized by enzymes including 15-hydroxyprostaglandin dehydrogenase to inactive metabolites (6-keto-PGF1alpha, 6,15-diketo-PGF1alpha, and 6,15-diketo-13,14-dihydro-PGF1alpha).
Primarily hepatic via acetylation (N-acetyltransferase 2, NAT2). Metabolites include hydralazine pyruvic acid hydrazone and acetylhydralazine.
Renal: 70% (as inactive metabolites); biliary/fecal: negligible.
Hydralazine is primarily metabolized in the liver via N-acetylation and hydroxylation. Approximately 80-90% of the drug is eliminated in urine as metabolites, with less than 10% excreted unchanged. A small fraction appears in feces via biliary excretion.
Approximately 50% bound to albumin.
85-90% bound primarily to albumin and alpha-1-acid glycoprotein.
0.03–0.1 L/kg; small Vd consistent with limited extravascular distribution.
1.5-2.0 L/kg. This high Vd indicates extensive tissue binding and accumulation in vascular smooth muscle.
Intravenous: 100% (only route of administration).
Oral: 10-30% due to extensive first-pass metabolism. Bioavailability is lower in fast acetylators. Bioavailability is 100% for intravenous administration.
No specific dose adjustment required; monitor fluid and electrolyte balance due to potential hypotension.
GFR 10-50 m L/min: administer every 8-12 hours; GFR <10 m L/min: administer every 12-24 hours.
No specific dose adjustment required; consider reduced clearance in severe hepatic impairment (Child-Pugh class C) with cautious titration.
Child-Pugh A: caution, consider starting at 25% of normal dose; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated.
Initial: 2 ng/kg/min via continuous IV infusion, titrate by 1-2 ng/kg/min every 15 minutes as tolerated. Maximum dose not established; typical range 5-40 ng/kg/min.
0.75-1 mg/kg/day orally divided every 6-12 hours, maximum 7.5 mg/kg/day; intravenous: 0.1-0.2 mg/kg/dose every 4-6 hours as needed.
No specific dose adjustment; start at lower end of dosing range (4 ng/kg/min) and titrate cautiously due to increased sensitivity to hemodynamic effects.
Start at 10 mg orally twice daily, increase slowly; monitor for hypotension and reflex tachycardia; maximal dose 200 mg/day.
FLOLAN is a potent vasodilator and must be administered by continuous IV infusion through a permanent central venous catheter. Abrupt discontinuation or sudden large dose reductions may result in worsening pulmonary hypertension and death. Only clinicians experienced in PAH treatment should prescribe FLOLAN.
Systemic lupus erythematosus-like syndrome (drug-induced lupus) with long-term use at high doses.
Do not abruptly discontinue infusion (risk of rebound pulmonary hypertension), monitor for pulmonary edema (if suspect veno-occlusive disease), may cause bleeding complications (due to antiplatelet effects), monitor for sepsis/thrombosis from chronic IV catheter, use caution in patients with hepatic or renal impairment.
May cause drug-induced lupus erythematosus; discontinue if symptoms develop.,Peripheral neuritis (pyridoxine deficiency) with long-term use.,May precipitate angina or myocardial infarction in patients with coronary artery disease.,Tachycardia and palpitations may occur; use with beta-blockers if needed.,Blood dyscrasias (rare).
Long-term use in patients with pulmonary veno-occlusive disease (PVOD), hypersensitivity to epoprostenol or structurally related drugs, or severe left ventricular systolic dysfunction (NYHA Class III-IV heart failure) due to risk of pulmonary edema.
Hypersensitivity to hydralazine,Coronary artery disease (angina pectoris, myocardial infarction),Mitral valve rheumatic heart disease,Aortic aneurysm (relative)
No specific food interactions are reported for epoprostenol. Avoid excessive alcohol as it may worsen hypotension.
Take with food or milk to reduce stomach upset and slow absorption. Avoid high-tyramine foods (e.g., aged cheese, cured meats, fermented products) if taking a combination product containing hydralazine and hydrochlorothiazide–though hydralazine alone has no known significant food interactions. Limiting salt intake enhances antihypertensive effect.
FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; however, no adequate and well-controlled studies in pregnant women. Epoprostenol is a potent vasodilator and inhibitor of platelet aggregation; theoretical risk of hemorrhage in the fetus. Use only if clearly needed.
FDA Pregnancy Category C. First trimester: No well-controlled studies; animal studies show no evidence of teratogenicity but embryotoxicity at high doses. Second/Third trimesters: Associated with maternal hypotension potentially reducing placental perfusion; no fetal malformations reported, but neonatal thrombocytopenia, lupus-like syndrome, and arrhythmias reported with chronic use near term.
Epoprostenol is not recommended during breastfeeding. No data on presence in human milk, effects on the breastfed infant, or milk production. Due to potential for serious adverse reactions (e.g., hypotension, bleeding), breastfeeding should be discontinued during treatment.
Excreted into breast milk in small amounts (M/P ratio estimated 1.0-1.4). No reported adverse effects in infants. American Academy of Pediatrics considers compatible with breastfeeding. Monitor infant for hypotensive effects or drug accumulation, especially in neonates or preterm infants.
Pregnancy may alter pharmacokinetics; increase in plasma volume may require dose adjustments. No formal studies; titrate dose based on clinical response (e.g., symptoms of pulmonary arterial hypertension). Monitor for signs of overdose (hypotension, tachycardia) or underdose (worsening dyspnea).
Increased volume of distribution and plasma clearance may require dose adjustments. Initial oral: 10 mg 4 times daily, titrate up to 300 mg/day. In severe hypertension, IV bolus (5-10 mg) may be used with caution. Monitor for reflex tachycardia and hypotension; dose titration based on maternal response.
FLOLAN (epoprostenol) is a prostacyclin used for pulmonary arterial hypertension (PAH). It has a very short half-life (3-5 minutes) and must be administered via continuous IV infusion. Abrupt interruption can cause life-threatening rebound pulmonary hypertension. The drug is unstable at room temperature; requires ice packs during administration. Dose titration is done based on symptoms and side effects (e.g., jaw pain, flushing, headache, diarrhea).
Hydralazine is a direct-acting vasodilator; first dose may cause profound hypotension—administer with food to减缓 absorption. Monitor for drug-induced lupus (especially in slow acetylators); baseline ANA recommended. Tachyphylaxis occurs; combine with beta-blocker and diuretic to counteract reflex tachycardia and fluid retention. Adjust dose in renal impairment (creatinine clearance < 10 m L/min).
This medication is given continuously through an intravenous (IV) line using a portable infusion pump.,Never stop the infusion suddenly; sudden stoppage can cause severe worsening of your condition.,Keep the medication cold (with ice packs) during infusion; it degrades at room temperature.,Report any signs of infection at the IV site, such as redness, swelling, or pain.,Common side effects include headache, jaw pain, flushing, nausea, and diarrhea; these may improve over time.
Take this medication exactly as prescribed, usually 3-4 times daily. Swallow tablets whole with a glass of water.,Do not stop taking this drug suddenly, as this may cause a rapid increase in blood pressure.,This medication may cause dizziness or lightheadedness, especially when getting up from a sitting or lying position. Rise slowly.,Report any unexplained fever, joint pain, rash, or sore throat to your healthcare provider immediately—these could be signs of a lupus-like reaction.,Avoid alcohol, as it can increase side effects like dizziness or drowsiness.,If you miss a dose, take it as soon as you remember unless it is almost time for the next dose. Do not double the dose.
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 FLOLAN vs Hydralazine, answered by our medical review team.
FLOLAN is a Prostacyclin Vasodilator that works by Epoprostenol is a prostaglandin I2 (prostacyclin) analogue that directly vasodilates pulmonary and systemic arterial beds, inhibits platelet aggregation, and has antiproliferative effects on vascular smooth muscle.. Hydralazine is a Vasodilator that works by Hydralazine is a direct-acting vasodilator that relaxes arteriolar smooth muscle, leading to decreased peripheral vascular resistance and blood pressure. Its exact mechanism is unclear but may involve interference with calcium movement and increased c GMP levels.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FLOLAN and Hydralazine 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 FLOLAN is: Initial: 4 ng/kg/min via continuous IV infusion, then titrated in increments of 1-2 ng/kg/min at intervals of at least 15 minutes based on clinical response. Typical maintenance dose: 20-40 ng/kg/min; range: 10-80 ng/kg/min.. The standard adult dose of Hydralazine is: 10-50 mg orally every 6 hours, titrate to maximum 300 mg/day; 10-20 mg intramuscularly or intravenously every 4-6 hours as needed.. 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 FLOLAN and Hydralazine 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. FLOLAN is classified as Category C. FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; however, no adequate and well-controlled studies in pregnant women. Epoprostenol is a potent vasodilator . Hydralazine is classified as Category A/B. FDA Pregnancy Category C. First trimester: No well-controlled studies; animal studies show no evidence of teratogenicity but embryotoxicity at high doses. Second/Third trimesters: . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.