Gramicidin
Also known as: Gramicidin D, Gramicidin A/B/C, linear gramicidin, gramicidine, Neosporin (combination)
Antimicrobial peptide / pore-forming ion channel peptide
What it is
Gramicidin is found in topical antibiotic eye drops and skin ointments used to treat bacterial infections of the eye and skin. It is most often combined with neomycin and polymyxin B in products like Neosporin ophthalmic drops. It is not taken by injection or by mouth.
The scientific side
gramicidin is a small linear antimicrobial peptide that exerts its effects primarily by forming transmembrane ion channels in bacterial lipid bilayers. The abstracts describe gramicidin A (gA) as a pore-forming peptide capable of self-assembling within phospholipid bilayers to produce conducting dimers that span the membrane. Once incorporated, each gramicidin A channel allows uncontrolled cation flux—particularly monovalent ions such as potassium and sodium—across the bacterial membrane, disrupting cellular ion homeostasis and ultimately causing bacterial cell death. The channel forms when two gramicidin A monomers from opposite membrane leaflets dimerize head-to-head, creating a narrow aqueous pore approximately 0.4 nm in diameter. Studies using quartz crystal microbalance with dissipation (QCM-D) showed that at low peptide concentrations gramicidin D induces mild outer-leaflet softening consistent with beta-6.3 channel formation, while at higher concentrations it drives mechanically disruptive remodeling of supported lipid bilayers. Raman microscopy studies confirmed that gramicidin A incorporation into phospholipid vesicles causes concentration-dependent disordering of membrane acyl chains, reflecting hydrophobic mismatch between the rigid channel structure and surrounding lipids, with approximately 7–8 boundary lipids perturbed per channel. The channel's conductance and lifetime are modulated by membrane composition and peripheral protein adsorption: bovine serum albumin adsorption to membranes was shown to increase the average number and lifetime of conducting gramicidin A dimers by shifting the monomer-dimer equilibrium. Endocannabinoid studies using gramicidin A currents as a readout of membrane physical properties demonstrated that lipid bilayer elasticity and hydrophobic thickness regulate channel function. Because gramicidin acts by disrupting membrane integrity rather than targeting a specific receptor, its antibacterial spectrum is broad but its systemic toxicity is high, confining clinical use to topical ophthalmic and dermatological formulations.
Class: Antimicrobial peptide / pore-forming ion channel peptide
Administration & storage
- Administration
- None identified in the fetched abstracts. Systemic gramicidin administration is not described in any retrieved clinical study. Gramicidin is toxic when administered parenterally and is confined to topical use.
- Storage
- No specific storage conditions for gramicidin formulations are reported in the fetched abstracts. Standard ophthalmic preparation handling (room temperature, protect from light, discard after stated expiry) is implied by the product descriptions in the clinical studies.
Legal & regulatory status
Gramicidin is approved as an over-the-counter and prescription topical antimicrobial ingredient in combination ophthalmic products (e.g., neomycin-polymyxin B-gramicidin eye drops). It is not approved for systemic or…
Gramicidin is not listed as a prohibited substance by WADA. It is a topically administered antibiotic with no performance-enhancing indication identified in the fetched abstracts.
Gramicidin-containing combination ophthalmic drops are marketed in Canada as prescription topical antibiotics. No injectable or systemic formulations are approved. No specific Canadian regulatory data found in the…
What it's studied for
- Topical treatment of bacterial corneal ulceration Tier 2 — Controlled clinical studies
- Post-cataract-surgery prophylaxis and inflammation control (comparator arm) Tier 2 — Randomized controlled trial
- Treatment of bacterial keratitis in resource-limited settings Tier 2 — Randomized controlled trial
- Ophthalmic antibiotic for hordeolum (stye) after incision and curettage Tier 3 — Small randomized pilot trial
- Decontamination of donor eyes before corneal transplantation Tier 3 — Comparative laboratory/clinical study
- Model ion channel for membrane biophysics research Tier 4 — Preclinical/mechanistic research only
- Probe of membrane physical properties in pharmacology research Tier 4 — Preclinical/mechanistic research only
Safety signals
- Ocular allergic reactions
- Topical toxic or allergic reactions during corneal ulcer treatment
- Membrane disruption at higher concentrations (mechanistic toxicity signal)
- Systemic toxicity precluding parenteral use
- Potential for inferior anti-inflammatory outcomes when used without a steroid post-surgery
- Bilayer lipid disordering at therapeutic concentrations
All studies (1)
Frequently asked
Can gramicidin be injected or used for anything other than eye drops or ointments?
Based on the published studies retrieved, gramicidin is only studied and used clinically as a topical ophthalmic or dermatological agent. Its mechanism—forming non-selective ion channels in lipid membranes—makes it toxic to all cell types at systemic concentrations. No clinical study of injectable or oral gramicidin was identified in the retrieved literature. Use is limited to products applied directly to the eye or skin.
How does gramicidin kill bacteria?
gramicidin works by inserting itself into bacterial cell membranes and forming narrow tubular pores. Two gramicidin molecules join end-to-end to span the membrane, allowing ions like sodium and potassium to flow freely across it. This disrupts the electrical and chemical gradients the bacterium needs to survive, leading to cell death. At higher concentrations it also physically disrupts the membrane structure itself.
Is gramicidin effective for treating eye infections on its own?
Based on the retrieved abstracts, gramicidin is almost always used in combination with other antibiotics (typically neomycin and polymyxin B) rather than alone. The combination provides broader coverage against gram-positive and gram-negative bacteria. Clinical trials studied the combination product, not gramicidin in isolation, so the individual contribution of gramicidin to treatment outcomes cannot be determined from the available evidence.
What bacteria does gramicidin treat?
Based on the clinical studies retrieved, gramicidin-containing combination eye drops have been studied against infections caused by Staphylococcus aureus and Pseudomonas aeruginosa (the most common organisms in bacterial corneal ulcer studies), as well as coagulase-negative Staphylococcus and Acinetobacter species. The retrieved abstracts do not provide a comprehensive spectrum for gramicidin alone, as it was always studied in combination formulations.
Does gramicidin have any role in sports or performance enhancement?
Based on the retrieved literature, gramicidin has no identified role in sports performance or physical enhancement. It is a topical antibiotic used for eye and skin infections. It is not mentioned in any performance-enhancement context in the retrieved abstracts, and it is not on the WADA prohibited list.