Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
NITROGLYCERIN vs ISMO
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Nitroglycerin is a vasodilator that is converted to nitric oxide (NO) in vascular smooth muscle cells. NO activates guanylyl cyclase, increasing c GMP levels, leading to dephosphorylation of myosin light chains and vasodilation. Predominantly dilates venous capacitance vessels, reducing preload; also dilates coronary arteries at higher doses.
Isosorbide mononitrate is a nitrate that dilates coronary arteries and peripheral veins. It acts by releasing nitric oxide, which activates guanylate cyclase, increasing c GMP levels, leading to smooth muscle relaxation and vasodilation.
Acute angina pectoris,Prophylaxis of angina pectoris,Acute myocardial infarction (IV formulation),Heart failure associated with acute myocardial infarction (IV),Anal fissure (topical, off-label),Esophageal spasm (off-label)
Prevention of angina pectoris due to coronary artery disease,Off-label: Treatment of acute angina (immediate-release forms)
Sublingual: 0.3-0.6 mg every 5 minutes up to 3 doses for angina; Transdermal: 0.2-0.8 mg/hour patch applied daily for 12-14 hours; Intravenous: 5-200 mcg/min continuous infusion for acute coronary syndromes or heart failure; Topical 2% ointment: 15-30 mg (0.5-1 inch) every 6-8 hours.
20 mg orally twice daily, 7 hours apart (e.g., 8 AM and 3 PM) to minimize nitrate tolerance.
Terminal half-life: 1–4 minutes for the parent compound; clinical effects dissipate within the same time frame, correlating with rapid metabolism.
Terminal elimination half-life is approximately 5-6 hours. In elderly patients or those with hepatic impairment, half-life may be prolonged (up to 8-10 hours), warranting dose adjustment.
Metabolized primarily by hepatic glutathione-organic nitrate reductase and cytochrome P450 enzymes (CYP3A4) to inorganic nitrite and denitrated metabolites; also undergoes extrahepatic metabolism in erythrocytes and vascular tissue.
Primarily metabolized in the liver by denitration; minor metabolism via glucuronidation. Metabolites are inactive.
Metabolized extensively by hepatic glutathione-organic nitrate reductase and other non-specific esterases; renal excretion of metabolites accounts for approximately 50%, with fecal elimination of about 20-30%. Less than 1% of unchanged drug is excreted renally.
Primarily renal; 80-90% of the dose is excreted as inactive metabolites (isosorbide mononitrate and isosorbide dinitrate) in urine. Less than 1% is excreted unchanged. Fecal excretion is minimal.
Approximately 60% bound to albumin.
Approximately 30% bound to plasma proteins, primarily albumin.
Approximately 3.3 L/kg, indicating extensive distribution into tissues.
Vd is 0.6-0.9 L/kg, indicating distribution into total body water. Higher Vd may be observed in patients with heart failure.
Sublingual: 40–60% due to first-pass metabolism; buccal: 40–60%; transdermal: 10–20% (limited by skin permeability).
Oral: 90-100% (sustained-release formulations). Sublingual: high but variable; generally effective due to extensive absorption.
No dose adjustment required for any degree of renal impairment, including end-stage renal disease.
No dose adjustment required for GFR ≥30 m L/min. For GFR <30 m L/min, consider reducing dose to 10 mg twice daily due to potential accumulation of active metabolite.
Child-Pugh Class A: No adjustment; Child-Pugh Class B: Consider 25% dose reduction; Child-Pugh Class C: Avoid use or use with extreme caution, consider 50% dose reduction.
No dose adjustment in Child-Pugh A or B. For Child-Pugh C, reduce dose to 10 mg twice daily and monitor for hypotension.
Safety and efficacy not established; limited data: IV infusion 0.25-1 mcg/kg/min titrated to effect; sublingual 5-10 mcg/kg per dose (max 0.6 mg) every 5-10 minutes as needed for angina.
Safety and efficacy not established; no standard dosing recommendations.
Start at lowest dose; sublingual 0.3 mg, transdermal 0.2 mg/hour; increased sensitivity to hypotension and syncope; monitor for orthostatic hypotension; may require reduced dosing frequency.
Start at 10 mg twice daily with gradual titration based on tolerance and renal function. Monitor for hypotension and dizziness.
Do not use nitroglycerin with phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil) as this can cause severe hypotension. Concomitant use with soluble guanylyl cyclase stimulators (e.g., riociguat) is contraindicated.
Do not use with phosphodiesterase-5 (PDE-5) inhibitors (e.g., sildenafil, tadalafil) due to risk of severe hypotension.
Hypotension,Tachycardia,Paradoxical bradycardia,Increased intracranial pressure (use with caution in cerebral hemorrhage or head trauma),Hypertrophic cardiomyopathy (may exacerbate outflow obstruction),Tolerance with prolonged use (intermittent dosing with nitrate-free interval recommended),Abrupt withdrawal may precipitate angina
Hypotension and reflex tachycardia may occur,Caution in patients with volume depletion or hypotension,May cause headaches; tolerance may develop with prolonged use,Abrupt withdrawal may increase angina frequency
Hypersensitivity to nitroglycerin or any component,Concomitant use with phosphodiesterase-5 inhibitors (within 24 hours for sildenafil, vardenafil; 48 hours for tadalafil),Concomitant use with soluble guanylyl cyclase stimulators (riociguat),Severe anemia,Increased intracranial pressure (e.g., head trauma, cerebral hemorrhage),Constrictive pericarditis,Pericardial tamponade,Restrictive cardiomyopathy,Acute myocardial infarction with low left ventricular filling pressure,Circulatory failure (shock)
Concurrent use of PDE-5 inhibitors,Severe anemia,Closed-angle glaucoma,Hypersensitivity to isosorbide mononitrate or nitrates,Acute myocardial infarction with low filling pressures
Avoid alcohol consumption while taking nitroglycerin due to risk of severe hypotension and syncope. No other significant food interactions.
Alcohol may enhance hypotension risk. Avoid high-fat meals if extended-release formulation, as they may affect absorption. No other significant food interactions.
Insufficient human data; animal studies do not indicate teratogenicity. Avoid in first trimester unless clearly needed. No known increased risk of major malformations. Use caution in third trimester due to potential maternal hypotension reducing uteroplacental perfusion.
ISMO (isosorbide mononitrate) is categorized as FDA Pregnancy Category C. In animal studies, reduced fetal survival and growth retardation were observed at high doses. No adequate human studies exist. Use only if potential benefit justifies risk. First trimester: Theoretical risk of hemodynamic effects; avoid unless necessary. Second/third trimester: May cause fetal hypoxia due to maternal hypotension; monitor fetal heart rate. Peripartum: May exacerbate uterine relaxation and postpartum hemorrhage if used near delivery.
Excreted into breast milk in very low amounts; M/P ratio not established. Considered compatible with breastfeeding; monitor infant for hypotension.
Excretion into human milk is unknown. Due to risk of infant methemoglobinemia and hypotension, caution is advised. M/P ratio: Not available. American Academy of Pediatrics considers nitrate derivatives compatible with breastfeeding, but monitor infant for cyanosis and lethargy.
No routine dose adjustment required; however, increased plasma volume may necessitate higher doses for therapeutic effect. Monitor clinical response.
No specific dose adjustments for ISMO in pregnancy are established due to lack of pharmacokinetic studies. However, pregnancy-induced hemodynamic changes (increased plasma volume, cardiac output) may reduce efficacy; consider dose titration based on clinical response. Avoid doses >60 mg/day to minimize hypotensive risk. Use immediate-release formulations for flexible dosing if needed.
Use with caution in patients with hypertrophic obstructive cardiomyopathy due to risk of syncope. Nitroglycerin is contraindicated with phosphodiesterase-5 inhibitors (e.g., sildenafil) due to severe hypotension. Sublingual tablets should be taken at first sign of angina; if pain persists after 5 minutes, call 911. Tolerance develops with continuous exposure, so use nitrate-free intervals (10-12 hours daily) for transdermal patches. Administer intravenous nitroglycerin with non-PVC tubing to avoid drug absorption. Monitor for hypotension, reflex tachycardia, and headache. Do not use in patients with severe anemia, increased intracranial pressure, or right ventricular infarction.
ISMO (isosorbide mononitrate) is a nitrate used for angina prophylaxis, not for acute attacks. Tolerance develops with sustained use; maintain a 10-12 hour nitrate-free interval to prevent tolerance. Do not use with phosphodiesterase-5 inhibitors (e.g., sildenafil) due to risk of profound hypotension. Contraindicated in severe anemia, increased intracranial pressure, or hypertrophic obstructive cardiomyopathy. Discontinue if blurred vision or dry mouth occurs.
Take sublingual nitroglycerin at the first sign of chest pain; sit down before taking to prevent dizziness.,Place the tablet under the tongue or in the buccal pouch and allow it to dissolve completely; do not swallow.,If pain is not relieved within 5 minutes, call 911 immediately; you may take a second tablet while waiting.,Do not take this medication if you have taken erectile dysfunction drugs (e.g., sildenafil, tadalafil) within the last 24-48 hours.,Store sublingual tablets in the original glass bottle with the cap tightly closed to protect from light and moisture; do not transfer to another container.,Expect a headache or flushing after taking; these usually diminish with continued use.,If using a transdermal patch, apply to a hairless area of skin and rotate sites daily; remove at bedtime to prevent tolerance.,Avoid alcohol while taking this medication as it can increase the risk of hypotension.,Seek emergency help if you experience severe dizziness, fainting, or difficulty breathing.
Take as prescribed to prevent angina; do not use for acute attacks.,May cause headache, dizziness, or hypotension; rise slowly from sitting.,Avoid taking erectile dysfunction drugs (e.g., sildenafil, tadalafil) as severe blood pressure drop can occur.,Do not stop abruptly to avoid rebound angina.,Store in original container away from light and moisture.
"Concomitant use of nitroglycerin, a vasodilator that increases cyclic guanosine monophosphate (cGMP) in vascular smooth muscle, and acebutolol, a cardioselective beta-1 adrenergic blocker, can lead to excessive hypotension and reflex tachycardia. Acebutolol may blunt the compensatory sympathetic response to nitroglycerin-induced vasodilation, while nitroglycerin can counteract the negative chronotropic effects of acebutolol, resulting in unopposed vagal tone and potential bradycardia. This interaction increases the risk of syncope, dizziness, and cardiovascular collapse, particularly in patients with volume depletion or pre-existing heart failure."
"Amobarbital, a barbiturate with hepatic enzyme-inducing properties, may enhance the metabolism of nitroglycerin, potentially reducing its efficacy. However, the primary concern is that amobarbital can cause significant hypotension via central nervous system depression and vasodilation, which, when combined with the vasodilatory effects of nitroglycerin, may lead to additive hypotensive effects, increasing the risk of severe hypotension, syncope, and cardiovascular collapse. This interaction is particularly relevant in patients with coronary artery disease or heart failure, where maintaining adequate blood pressure is critical."
"Concurrent administration of clofarabine, a purine nucleoside antimetabolite, and nitroglycerin, a vasodilator for angina, may lead to additive hypotension. Clofarabine itself can induce hypotension as an adverse effect, and nitroglycerin directly relaxes vascular smooth muscle, resulting in decreased blood pressure. This combination increases the risk of severe hypotension, potentially leading to dizziness, syncope, or falls, especially in patients with pre-existing hypotension or volume depletion."
"Bosentan, a dual endothelin receptor antagonist and an inducer of CYP3A4 and CYP2C9, reduces systemic exposure to vismodegib, a Hedgehog pathway inhibitor primarily metabolized by CYP3A4. This interaction leads to decreased serum concentrations of vismodegib, potentially diminishing its antitumor efficacy in patients with advanced basal cell carcinoma. Concomitant use may require vismodegib dose adjustment or alternative therapies to avoid therapeutic failure."
"Vismodegib inhibits CYP3A4, which is the primary enzyme responsible for metabolizing nilotinib. Concomitant administration may lead to increased nilotinib plasma concentrations, elevating the risk of QT interval prolongation, torsades de pointes, hepatotoxicity, and myelosuppression. Clinical vigilance is warranted due to the narrow therapeutic index of nilotinib."
"Vismodegib, a hedgehog pathway inhibitor, is a moderate inhibitor of CYP2C9, the primary enzyme responsible for metabolizing tolbutamide. Concomitant use can significantly decrease tolbutamide clearance, leading to elevated plasma concentrations and prolonged hypoglycemic effects. This increases the risk of severe hypoglycemia, especially in diabetic patients, and may require dose adjustment of tolbutamide."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about NITROGLYCERIN vs ISMO, answered by our medical review team.
NITROGLYCERIN is a Nitrate Vasodilator that works by Nitroglycerin is a vasodilator that is converted to nitric oxide (NO) in vascular smooth muscle cells. NO activates guanylyl cyclase, increasing c GMP levels, leading to dephosphorylation of myosin light chains and vasodilation. Predominantly dilates venous capacitance vessels, reducing preload; also dilates coronary arteries at higher doses.. ISMO is a Nitrate Vasodilator that works by Isosorbide mononitrate is a nitrate that dilates coronary arteries and peripheral veins. It acts by releasing nitric oxide, which activates guanylate cyclase, increasing c GMP levels, leading to smooth muscle relaxation and vasodilation.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between NITROGLYCERIN and ISMO depend on the specific clinical indication. These are both Nitrate Vasodilator agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of NITROGLYCERIN is: Sublingual: 0.3-0.6 mg every 5 minutes up to 3 doses for angina; Transdermal: 0.2-0.8 mg/hour patch applied daily for 12-14 hours; Intravenous: 5-200 mcg/min continuous infusion for acute coronary syndromes or heart failure; Topical 2% ointment: 15-30 mg (0.5-1 inch) every 6-8 hours.. The standard adult dose of ISMO is: 20 mg orally twice daily, 7 hours apart (e.g., 8 AM and 3 PM) to minimize nitrate tolerance.. 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 NITROGLYCERIN and ISMO 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. NITROGLYCERIN is classified as Category C. Insufficient human data; animal studies do not indicate teratogenicity. Avoid in first trimester unless clearly needed. No known increased risk of major malformations. Use caution . ISMO is classified as Category C. ISMO (isosorbide mononitrate) is categorized as FDA Pregnancy Category C. In animal studies, reduced fetal survival and growth retardation were observed at high doses. No adequate . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.