Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BETHKIS 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
Tobramycin, an aminoglycoside antibiotic, binds to the 30S ribosomal subunit, causing misreading of m RNA and inhibiting protein synthesis, leading to bacterial cell death.
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.
Management of cystic fibrosis patients with Pseudomonas aeruginosa infection
Topical treatment of bacterial infections of the skin and eye (e.g., conjunctivitis, keratitis, blepharitis),Prophylaxis of minor wounds, cuts, and abrasions
4 IU/kg (1 mg/kg) intramuscularly or subcutaneously once weekly for 4 weeks, then a maintenance dose of 2 IU/kg (0.5 mg/kg) once weekly.
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 2-3 hours in patients with normal renal function; prolonged to 20-40 hours in severe renal impairment (Cr Cl <30 m L/min).
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 excreted unchanged in urine via glomerular filtration; minimal hepatic metabolism.
Not systemically absorbed after topical administration; no significant metabolism.
Primarily renal excretion of unchanged drug via glomerular filtration; ~90% of absorbed dose excreted in urine within 24 hours; biliary/fecal elimination <5%.
Neomycin: ~99% renal; polymyxin B: ~60% renal, 40% fecal; bacitracin: mainly renal (over 90%). Combined: renal (predominant), with minor biliary/fecal contribution (polymyxin B).
Low protein binding: 10-20%; primarily binds to albumin.
Neomycin: 0-20%; polymyxin B: 60-80% (alpha-1-acid glycoprotein, albumin); bacitracin: <5%. Combined: ~40-50% bound overall.
0.2-0.4 L/kg; distributes primarily into extracellular fluid; limited intracellular penetration.
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.
Inhalation: ~50-60% of nominal dose reaches systemic circulation; oral: negligible (<1% due to poor gastrointestinal absorption).
Topical/ophthalmic/otic: negligible systemic absorption (<0.1%).
No dose adjustment required for renal impairment. Not removed by hemodialysis.
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.
No dose adjustment recommended for mild to moderate hepatic impairment (Child-Pugh A or B). Use with caution in severe hepatic impairment (Child-Pugh C) due to lack of data.
No adjustment needed for topical use. No systemic effects expected.
Weight-based dosing: 4 IU/kg (1 mg/kg) intramuscularly or subcutaneously once weekly for 4 weeks, then 2 IU/kg (0.5 mg/kg) once weekly. Safety and efficacy in children <18 years not established.
Same as adult dosing for topical use. For neonates, use with caution on large surface areas; avoid prolonged use.
No specific dose adjustments recommended. Use with caution due to potential age-related decline in renal and hepatic function. Monitor for adverse effects.
No specific age-related adjustments. Use with caution on fragile skin; apply sparingly to avoid systemic absorption.
Risk of nephrotoxicity and ototoxicity; monitor renal function and hearing during therapy.
None.
Nephrotoxicity, ototoxicity (vestibular and auditory), neuromuscular blockade, hypersensitivity, superinfection.
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 tobramycin or other aminoglycosides.
Hypersensitivity to any component of the product.,Otic use if tympanic membrane is perforated (risk of ototoxicity).
No specific food interactions. Maintain adequate hydration; avoid excessive salt intake if concurrent diuretics are used.
No known food interactions with topical application.
Insufficient human data; animal studies show no teratogenic effects at doses up to 4 times the human dose. Risk cannot be ruled out; use only if clearly needed.
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.
Unknown if excreted in human breast milk; M/P ratio not available. Caution advised due to risk of infant bowel flora alteration and potential for tobramycin-related ototoxicity or nephropathy.
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.
No specific dose adjustments recommended; pharmacokinetics may be altered due to increased volume of distribution and GFR; monitor serum levels and adjust to maintain therapeutic trough <2 mcg/m L.
No dosage adjustment required for topical use; systemic absorption is negligible. Use standard dosing as per non-pregnant adults.
Administer via inhalation only using a suitable nebulizer; do not mix with other drugs in the nebulizer. Monitor for bronchospasm; consider pretreatment with a bronchodilator in patients with reactive airway disease. Assess renal function before and during therapy due to potential nephrotoxicity. Obtain audiometric testing at baseline and periodically due to ototoxicity risk. Avoid concurrent use of loop diuretics or other nephrotoxic drugs. Trough serum tobramycin concentrations should be measured after 2–3 doses when systemic absorption is suspected.
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.
Use Bethkis exactly as prescribed; do not skip doses or double up.,Do not swallow or inject Bethkis; it is for inhalation only.,Use a nebulizer with a mouthpiece; do not use a face mask unless necessary.,Store vials in the refrigerator; protect from light.,Clean and disinfect the nebulizer after each use.,Report hearing loss, ringing in the ears, dizziness, or changes in urine output immediately.,Avoid other inhaled medications within 30 minutes of Bethkis unless directed.,Inform your healthcare provider of all other medications, especially diuretics and other antibiotics.
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 BETHKIS vs BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE, answered by our medical review team.
BETHKIS is a Aminoglycoside Antibiotic that works by Tobramycin, an aminoglycoside antibiotic, binds to the 30S ribosomal subunit, causing misreading of m RNA and inhibiting protein synthesis, leading to bacterial cell death.. 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 BETHKIS and BACITRACIN ZINC-NEOMYCIN SULFATE-POLYMYXIN B SULFATE depend on the specific clinical indication. These are both Aminoglycoside Antibiotic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of BETHKIS is: 4 IU/kg (1 mg/kg) intramuscularly or subcutaneously once weekly for 4 weeks, then a maintenance dose of 2 IU/kg (0.5 mg/kg) once weekly.. 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 BETHKIS 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. BETHKIS is classified as Category C. Insufficient human data; animal studies show no teratogenic effects at doses up to 4 times the human dose. Risk cannot be ruled out; use only if clearly needed.. 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.