Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
METHERGINE vs BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Methylergonovine is an ergot alkaloid that acts as a partial agonist at α-adrenergic receptors in the uterine smooth muscle, causing sustained contractions. It also exhibits serotonergic (5-HT2) and dopaminergic activity.
Bacitracin zinc inhibits bacterial cell wall synthesis by interfering with dephosphorylation of the lipid carrier that transports peptidoglycan precursors. Neomycin sulfate and polymyxin B sulfate are aminoglycoside and polypeptide antibiotics, respectively; neomycin binds to 30S ribosomal subunit and causes misreading of m RNA, while polymyxin B disrupts bacterial cell membrane permeability by interacting with phospholipids.
Prevention and treatment of postpartum hemorrhage due to uterine atony,Management of incomplete abortion
Topical treatment of bacterial infections of the skin and eye (e.g., conjunctivitis, keratitis, blepharitis),Prophylaxis of minor wounds, cuts, and abrasions
0.2 mg intramuscularly or intravenously after delivery of placenta and every 2-4 hours as needed, up to a maximum of 5 doses.
Apply topically (ointment or cream) to affected area 1-3 times daily. For ophthalmic use, instill 1-2 drops into affected eye(s) every 3-4 hours.
Terminal elimination half-life is approximately 2–3 hours in healthy adults; prolonged in hepatic impairment.
Neomycin: 2-3 h; polymyxin B: 4.5-6 h; bacitracin: 1.5 h. Combined: effectively ~2-6 h depending on renal function; clinical context: prolonged with renal impairment.
Primarily hepatic via CYP3A4 with significant first-pass metabolism; active metabolite is methylergonovine itself; excreted mainly in bile and urine.
Not systemically absorbed after topical administration; no significant metabolism.
Primarily hepatic metabolism; less than 1% excreted unchanged in urine. Biliary/fecal excretion accounts for ~80% of metabolites.
Neomycin: ~99% renal; polymyxin B: ~60% renal, 40% fecal; bacitracin: mainly renal (over 90%). Combined: renal (predominant), with minor biliary/fecal contribution (polymyxin B).
Approximately 93% bound, primarily to albumin and alpha-1-acid glycoprotein.
Neomycin: 0-20%; polymyxin B: 60-80% (alpha-1-acid glycoprotein, albumin); bacitracin: <5%. Combined: ~40-50% bound overall.
0.6 L/kg (range 0.3–0.8 L/kg), indicating moderate distribution into tissues.
Neomycin: ~0.25 L/kg; polymyxin B: ~0.5 L/kg; bacitracin: ~0.3 L/kg. Combined Vd ~0.3-0.5 L/kg, reflecting limited distribution mainly to extracellular fluid.
Oral bioavailability is approximately 10–20% due to extensive first-pass metabolism. Intramuscular administration provides 100% bioavailability.
Topical/ophthalmic/otic: negligible systemic absorption (<0.1%).
No specific dose adjustment recommended; use with caution in renal impairment due to risk of hypertension.
No systemic absorption with typical topical use; no adjustment necessary. For extensive use on damaged skin, monitor renal function and adjust if needed; no specific GFR-based guidelines.
Contraindicated in severe hepatic impairment (Child-Pugh class C). For Child-Pugh class A or B, use with caution and monitor for signs of toxicity.
No adjustment needed for topical use. No systemic effects expected.
Not recommended for pediatric use; safety and efficacy in children have not been established.
Same as adult dosing for topical use. For neonates, use with caution on large surface areas; avoid prolonged use.
Use with caution in elderly patients due to increased sensitivity to vasoconstrictive effects and higher risk of hypertension and myocardial ischemia.
No specific age-related adjustments. Use with caution on fragile skin; apply sparingly to avoid systemic absorption.
Not for use during pregnancy (except during delivery) due to risk of uterine tetany and fetal hypoxia. Contraindicated in patients with hypertension, preeclampsia, or eclampsia due to risk of severe hypertension and stroke.
None.
Risk of severe hypertension, especially in patients with preeclampsia, eclampsia, or hypertension.,Use with caution in patients with sepsis, hepatic or renal impairment, or coronary artery disease.,May cause ergotism with prolonged use or high doses (symptoms: vasospasm, ischemia).,Monitor blood pressure and uterine response during administration.
Prolonged use may result in overgrowth of nonsusceptible organisms including fungi.,Neomycin is ototoxic and nephrotoxic if absorbed systemically (e.g., applied to large areas of damaged skin).,Avoid contact with eyes other than for ophthalmic use.,Cross-allergenicity among aminoglycosides exists.
Hypersensitivity to ergot alkaloids,Pregnancy (for antepartum use),Hypertension, preeclampsia, or eclampsia,Peripheral vascular disease,Coronary artery disease,Severe hepatic or renal impairment,Sepsis
Hypersensitivity to any component of the product.,Otic use if tympanic membrane is perforated (risk of ototoxicity).
Avoid grapefruit juice as it may increase serum levels of methylergonovine via CYP3A4 inhibition. No specific food restrictions other than avoiding excessive caffeine intake, which may potentiate vasoconstrictive effects.
No known food interactions with topical application.
Methergine (methylergonovine) is contraindicated in pregnancy due to its oxytocic properties and risk of uterine hyperstimulation, fetal distress, and abortion. First trimester: potential teratogenic effects not well studied; avoid use. Second and third trimesters: can cause abruptio placentae, premature labor, and fetal anoxia. It is FDA Pregnancy Category X.
No evidence of teratogenicity in first trimester; animal studies show no fetal harm. Second and third trimester risk is low due to minimal systemic absorption from topical use. No known association with congenital anomalies.
Methylergonovine is excreted into breast milk in small amounts; the milk-to-plasma ratio is approximately 1.0. Adverse effects in nursing infants are rare but may include diarrhea, vomiting, and hypertension. It is generally considered compatible with breastfeeding when used short-term for postpartum hemorrhage. Avoid prolonged use.
Minimal systemic absorption suggests negligible excretion into breast milk; M/P ratio not determined. Considered compatible with breastfeeding by AAP; avoid application to breast area to prevent infant ingestion.
Not applicable; the drug is contraindicated during pregnancy. No dose adjustments are recommended for use during pregnancy as it should not be used.
No dosage adjustment required for topical use; systemic absorption is negligible. Use standard dosing as per non-pregnant adults.
METHERGINE (methylergonovine) is an ergot alkaloid used primarily for postpartum hemorrhage due to uterine atony. Do not use for routine induction of labor or for threatened abortion. Avoid in patients with hypertension, preeclampsia, coronary artery disease, or severe hepatic/renal disease. Monitor blood pressure closely during administration. Administer intramuscularly for rapid effect; onset is 2-5 minutes. Intravenous administration should be reserved for emergencies due to risk of hypertensive crisis. Contraindicated in pregnancy except immediately after delivery. Drug interactions: avoid concurrent use with strong CYP3A4 inhibitors (e.g., ketoconazole, macrolides, protease inhibitors) due to risk of ergotism and vasospasm. As of April 2025, there is no generic form; brand METHERGINE only.
OTC triple antibiotic ointment; avoid use on deep wounds, puncture wounds, or animal bites due to risk of toxicity and lack of efficacy. Neomycin carries the highest risk of allergic contact dermatitis among topical antibiotics; consider patch testing if prolonged use needed. Polymyxin B can cause neurotoxicity and nephrotoxicity if applied to large wounds or damaged skin. Not for use in eyes, ears, or mucous membranes. Do not exceed 7 days of continuous use.
This medication is used to prevent or treat excessive bleeding after childbirth by causing contractions of the uterus.,Report immediately if you experience severe headache, chest pain, vision changes, muscle cramps, or numbness/tingling in the arms or legs.,Avoid breastfeeding within 8 hours after the last dose if possible; if breastfeeding is necessary, pump and discard for 8 hours to reduce infant exposure.,Do not use this medication if you have uncontrolled high blood pressure, heart disease, or liver/kidney disease.,Avoid alcohol and grapefruit juice while on this medication as they may affect blood levels.,Take this medication exactly as prescribed; do not take double doses if a dose is missed.
Clean the affected area before applying a thin layer of ointment 1-3 times daily.,Do not use on large areas of skin, deep cuts, puncture wounds, or animal bites unless directed by a doctor.,Do not apply to eyes, nose, mouth, or inside ears.,Stop use and consult a doctor if rash or allergic reaction develops, condition worsens, or persists for more than 7 days.,Keep out of reach of children; seek medical attention if accidentally ingested.
No interactions on record
"Cisatracurium, a non-depolarizing neuromuscular blocking agent (NMBA), competitively blocks nicotinic acetylcholine receptors at the neuromuscular junction, causing skeletal muscle paralysis. Polymyxin B, a polypeptide antibiotic, can potentiate this neuromuscular blockade by reducing presynaptic acetylcholine release and stabilizing postsynaptic membranes, leading to prolonged and enhanced neuromuscular blockade. This interaction increases the risk of prolonged muscle paralysis, respiratory depression, and apnea, especially in patients with renal impairment or those receiving other NMBAs."
"Mecamylamine, a ganglionic blocking agent, potentiates the neuromuscular blocking effects of Polymyxin B, a polypeptide antibiotic. This interaction occurs through additive or synergistic inhibition of neuromuscular transmission, potentially leading to prolonged or intensified muscle relaxation, respiratory depression, and apnea. The clinical outcome may include enhanced toxicity, especially in patients with renal impairment or those receiving concurrent anesthetics or other neuromuscular blocking agents."
"Decamethonium, a depolarizing neuromuscular blocker, enhances the neuromuscular blocking effects of Polymyxin B, a polypeptide antibiotic that can also cause neuromuscular blockade via direct membrane stabilization and calcium channel inhibition. This additive pharmacodynamic interaction can lead to prolonged or enhanced muscle weakness, potentially resulting in respiratory paralysis and apnea. Clinically, this combination increases the risk of acute respiratory failure and may prolong recovery from neuromuscular blockade."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about METHERGINE vs BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE, answered by our medical review team.
METHERGINE is a Ergot Alkaloid Uterotonic that works by Methylergonovine is an ergot alkaloid that acts as a partial agonist at α-adrenergic receptors in the uterine smooth muscle, causing sustained contractions. It also exhibits serotonergic (5-HT2) and dopaminergic activity.. BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE is a Aminoglycoside Antibiotic that works by Bacitracin zinc inhibits bacterial cell wall synthesis by interfering with dephosphorylation of the lipid carrier that transports peptidoglycan precursors. Neomycin sulfate and polymyxin B sulfate are aminoglycoside and polypeptide antibiotics, respectively; neomycin binds to 30S ribosomal subunit and causes misreading of m RNA, while polymyxin B disrupts bacterial cell membrane permeability by interacting with phospholipids.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between METHERGINE and BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE 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 METHERGINE is: 0.2 mg intramuscularly or intravenously after delivery of placenta and every 2-4 hours as needed, up to a maximum of 5 doses.. The standard adult dose of BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE is: Apply topically (ointment or cream) to affected area 1-3 times daily. For ophthalmic use, instill 1-2 drops into affected eye(s) every 3-4 hours.. 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 METHERGINE and BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE 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. METHERGINE is classified as Category C. Methergine (methylergonovine) is contraindicated in pregnancy due to its oxytocic properties and risk of uterine hyperstimulation, fetal distress, and abortion. First trimester: po. BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE is classified as Category A/B. No evidence of teratogenicity in first trimester; animal studies show no fetal harm. Second and third trimester risk is low due to minimal systemic absorption from topical use. No . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.