Evidence Grade A — Regulatory approved. 3724 published studies. 9 registered clinical trials.
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Gramicidin is a topical antibiotic peptide found in combination eye drops such as Neosporin Ophthalmic Solution. It is far too toxic for systemic use but provides effective gram-positive bacterial coverage when applied directly to the eye surface. Historically, gramicidin is significant as one of the very first antibiotics ever discovered — its success in animals in 1939 was a key catalyst for the development of penicillin.
Gramicidin is also known by these brand and alternate names:
3,724 published studies: 518 human, 780 animal, 227 in-vitro, 147 reviews
Gramicidin is available in combination ophthalmic products such as Neosporin Ophthalmic Solution (with neomycin and polymyxin B), approved 1949. It provides gram-positive bacterial coverage in these combinations.
Gramicidin's significance extends well beyond its clinical use. It was the first antibiotic shown to cure systemic bacterial infections in animals (1939), and the demonstration that a natural substance could fight infection in living organisms was a key catalyst for the development of penicillin. In basic science, gramicidin remains the most-studied ion channel peptide, providing foundational understanding of how molecules transport ions across membranes.
Gramicidin has an extraordinary molecular mechanism that has made it one of the most studied peptides in biophysics. Its alternating D- and L-amino acids allow it to form a helix that spans the bacterial cell membrane. Two gramicidin molecules meet head-to-head inside the membrane, creating a tiny channel that allows ions to flood through uncontrollably — approximately six million ions per second. This destroys the bacterium's ability to maintain its internal chemistry, killing the cell. The channel is too toxic for systemic use but effective when applied topically.
Gramicidin's clinical evidence is entirely historical, predating modern trial standards by decades. Its safety and effectiveness as a topical ophthalmic antibiotic are supported by prolonged clinical experience rather than randomised controlled trials. The haemolytic (blood cell-destroying) activity that makes it unsuitable for systemic use is well documented. Outside clinical use, gramicidin is one of the most studied molecules in biophysics — the tiny ion channels it forms in cell membranes have been the subject of over 50 years of fundamental research. More recently, gramicidin's ability to accumulate in mitochondria and disrupt energy production has attracted interest in anticancer research, with laboratory screening of thousands of gramicidin variants aimed at reducing toxicity while retaining anti-tumour activity.
PeptideTrace tracks 9 registered clinical trials for Gramicidin sourced from ClinicalTrials.gov.
Safety, Tolerability, and Pharmacokinetic Profile of Grammidin, a Metered Dose Topical Spray in Healthy Volunteers
Safety, Tolerability, and Pharmacokinetic Profile of Grammidin With Anesthetic, a Metered Dose Topical Spray in Healthy Volunteers
Study to Evaluate the Efficacy and Safety of Different Doses of Graminidin With Anesthetic, a Metered Dose Topical Spray, in the Treatment of Acute Infectious and Inflammatory Pharyngeal Diseases Compared With Drug Septolete Total, Lozenges
Phage Therapy for the Prevention and Treatment of Wound Infections in Burned Patients
Frozen Versus Fresh Corneal Carriers for the Boston KPro Type I Donor Carriers
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Gramicidin D is a heterogeneous mixture of linear pentadecapeptides (15 AA): gramicidin A (~80%), B (~6%), C (~14%), from Brevibacillus brevis. MW ~1,882 Da. Strictly alternating D/L-amino acids, N-terminal formyl group, C-terminal ethanolamine, four tryptophans. Extremely hydrophobic (6 mg/L solubility). First commercially manufactured antibiotic (1939). Never used systemically (hemolytic). Ophthalmic 0.025 mg/mL q4h.
In lipid bilayers, each monomer adopts right-handed beta-6.3-helix. Two monomers dimerize head-to-head (N-to-N) via six H-bonds, spanning full membrane (~25-30 A) to form an ion channel (~4 A pore). Selective for monovalent cations (H+, Na+, K+), transporting ~6.3x10^6 ions/sec. Uncontrolled Na+ influx and K+ efflux collapse electrochemical gradient, causing depolarization and lysis.
Discovered 1939, FDA approved 1949. Available only in combination ophthalmic products: Neosporin Ophthalmic Solution (neomycin + polymyxin B + gramicidin). Contributes gram-positive coverage. Indication: superficial ocular infections, exclusively as combination product component. Historically catalyzed penicillin development for systemic use in the 1940s.
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