Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
RECTIV vs ISMO
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
RECTIV (nitroglycerin) is a nitric oxide (NO) donor that relaxes vascular smooth muscle via stimulation of intracellular cyclic guanosine monophosphate (c GMP) production, leading to vasodilation. In chronic anal fissures, it reduces internal anal sphincter pressure and improves blood flow to the anoderm.
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.
FDA-approved: Treatment of moderate to severe pain associated with chronic anal fissures
Prevention of angina pectoris due to coronary artery disease,Off-label: Treatment of acute angina (immediate-release forms)
1 gram (0.5 mg nitroglycerin) applied intrarectally as an ointment 10-15 minutes before anticipated bowel movement, up to twice daily.
20 mg orally twice daily, 7 hours apart (e.g., 8 AM and 3 PM) to minimize nitrate tolerance.
Terminal elimination half-life is approximately 2-4 hours in healthy adults. In patients with severe hepatic impairment, half-life may be prolonged up to 8-10 hours, requiring dose adjustment.
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.
Primarily hepatic metabolism via glutathione-organic nitrate reductase, with subsequent denitration and conjugation. Metabolites include inorganic nitrate and 1,2-glyceryl dinitrate. Also undergoes hydrolysis by esterases.
Primarily metabolized in the liver by denitration; minor metabolism via glucuronidation. Metabolites are inactive.
Primarily renal; approximately 60-70% of the parent drug and metabolites excreted in urine within 24 hours. Fecal elimination accounts for ~20-30% via biliary secretion. Less than 1% unchanged drug recovered in feces.
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 plasma proteins, primarily albumin. Binding is reversible and concentration-dependent.
Approximately 30% bound to plasma proteins, primarily albumin.
Volume of distribution is approximately 2-4 L/kg, indicating extensive tissue distribution. Clinical meaning: high Vd suggests significant uptake into vascular smooth muscle and other 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: approximately 40-50% due to first-pass metabolism. Oral: <10% due to extensive hepatic first-pass effect. Topical (RECTIV): systemic bioavailability is negligible (<1%) when applied as directed to the anal mucosa.
Oral: 90-100% (sustained-release formulations). Sublingual: high but variable; generally effective due to extensive absorption.
No dosage adjustment required for renal impairment. Use with caution in severe impairment due to potential for volume depletion.
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 A: no adjustment. Child-Pugh B: reduce dose to 1 gram (0.5 mg) once daily. Child-Pugh C: contraindicated.
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 in pediatric patients under 18 years.
Safety and efficacy not established; no standard dosing recommendations.
Use with caution; start at lowest effective dose (1 gram) and monitor for hypotension. Consider decreased renal/hepatic function.
Start at 10 mg twice daily with gradual titration based on tolerance and renal function. Monitor for hypotension and dizziness.
No FDA boxed warning.
Do not use with phosphodiesterase-5 (PDE-5) inhibitors (e.g., sildenafil, tadalafil) due to risk of severe hypotension.
Hypotension and syncope: Use with caution in patients with hypotension, hypovolemia, or those taking antihypertensives.,Severe anemia or conditions where vasodilation is detrimental.,Concomitant use with phosphodiesterase-5 (PDE-5) inhibitors (e.g., sildenafil) is contraindicated due to risk of severe hypotension.,May cause headaches and local burning or itching at application site.
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
Concomitant use of PDE-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil),History of hypersensitivity to nitroglycerin or any component of the formulation,Severe anemia,Increased intracranial pressure (e.g., head trauma, cerebral hemorrhage),Circulatory failure (shock) or severe hypotension
Concurrent use of PDE-5 inhibitors,Severe anemia,Closed-angle glaucoma,Hypersensitivity to isosorbide mononitrate or nitrates,Acute myocardial infarction with low filling pressures
No specific food restrictions. Avoid alcohol as it may worsen hypotension and headache. Grapefruit juice may increase nitroglycerin levels; avoid concurrent consumption.
Alcohol may enhance hypotension risk. Avoid high-fat meals if extended-release formulation, as they may affect absorption. No other significant food interactions.
Pregnancy Category B. No evidence of teratogenicity in animal studies at doses up to 10 mg/kg/day (approximately 50 times the recommended human dose). No well-controlled studies in pregnant women; use only if clearly needed. Fetal risk cannot be ruled out.
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.
Not recommended during breastfeeding. Drug is administered topically for hemorrhoids; systemic absorption is minimal, but no data on excretion in human milk. M/P ratio not determined.
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 dose adjustment required; pharmacokinetics not studied in pregnancy. Use the same dose as in non-pregnant patients, but with caution due to lack of safety data.
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.
RECTIV (nitroglycerin) 0.4% ointment is indicated for chronic anal fissure pain. Apply a 1-inch strip intra-anally every 12 hours for up to 8 weeks. May cause headache; monitor blood pressure. Contraindicated with PDE5 inhibitors (sildenafil, tadalafil, vardenafil) due to severe hypotension. Avoid in patients with hypotension (SBP <90 mm Hg) or hypovolemia. Do not use with strong CYP3A4 inhibitors (e.g., ritonavir, cobicistat).
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.
Apply 1-inch strip of ointment inside the anus every 12 hours using the applicator.,Wash hands before and after application.,Do not use more than 8 weeks unless directed by your doctor.,Avoid sexual activity during treatment as partner may absorb medication.,Do not take erectile dysfunction drugs (Viagra, Cialis, Levitra) while using this medication.,Seek medical help if you experience severe headache, dizziness, or fainting.,Store at room temperature away from heat and direct light.,Do not use if you have low blood pressure or are dehydrated.
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.
No interactions on record
"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 RECTIV vs ISMO, answered by our medical review team.
RECTIV is a Nitrate Vasodilator that works by RECTIV (nitroglycerin) is a nitric oxide (NO) donor that relaxes vascular smooth muscle via stimulation of intracellular cyclic guanosine monophosphate (c GMP) production, leading to vasodilation. In chronic anal fissures, it reduces internal anal sphincter pressure and improves blood flow to the anoderm.. 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 RECTIV 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 RECTIV is: 1 gram (0.5 mg nitroglycerin) applied intrarectally as an ointment 10-15 minutes before anticipated bowel movement, up to twice daily.. 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 RECTIV 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. RECTIV is classified as Category C. Pregnancy Category B. No evidence of teratogenicity in animal studies at doses up to 10 mg/kg/day (approximately 50 times the recommended human dose). No well-controlled studies in. 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.