Gramicidin — Complete Research Guide (2026)

Last updated 2026-06-30

What is Gramicidin?

Gramicidin (gramicidin D) is a linear peptide antibiotic that acts as a membrane ion-channel former and is active against Gram-positive bacteria. It is used only topically - in combination ophthalmic and skin preparations, for example alongside neomycin and polymyxin B - because it is hemolytic and toxic when given systemically.

The literature is dominated by older biophysical and mechanistic work plus a limited number of topical clinical studies; dedicated modern randomized controlled trials of gramicidin are sparse. Note that gramicidin S is a structurally distinct cyclic peptide and should not be confused with the linear channel-forming gramicidin used in topical products.

How does Gramicidin work?

Two gramicidin molecules span the bacterial membrane to form a cation-selective channel that dissipates transmembrane sodium and potassium gradients.

This collapses the electrochemical potential the cell needs to survive, killing the bacterium.

What does the research say about Gramicidin?

• Gramicidin kills Gram-positive bacteria by forming transmembrane ion channels that collapse the cell's ion gradients, a well-characterized membrane mechanism. ^[1]
• A topical framycetin/gramicidin preparation has been evaluated in a randomized clinical trial for external otitis, reflecting its use as a topical combination antibiotic. ^[3]
• Gramicidin D can enhance antibacterial activity in combination approaches, consistent with its membrane-permeabilizing action (in-vitro evidence). ^[5]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

• [1] The gramicidin ion channel: a model membrane protein — Kelkar DA et al., Biochimica et Biophysica Acta 2007. (Review (mechanism))
• [2] Gramicidin channels — Andersen OS et al., IEEE Transactions on Nanobioscience 2005. (Review (biophysics))
• [3] A randomized clinical trial of two topical preparations (framycitin/gramicidin and oxytetracycline/hydrocortisone with polymyxin B) in the treatment of external otitis — Wadsten CJ et al., Archives of Oto-Rhino-Laryngology 1985. (Randomized clinical trial (topical))
• [4] Gramicidin derivatives; toxicity; effect of proteins on hemolytic and bacteriostatic activity; antibacterial effect in vivo — Schales O et al., Archives of Biochemistry 1948. (Experimental (early antibacterial/toxicity))
• [5] Gramicidin D enhances the antibacterial activity of fluoride — Nelson JW et al., Bioorganic and Medicinal Chemistry Letters 2014. (In-vitro (antibacterial))
• [6] Structure, toxicity and antibiotic activity of gramicidin S and derivatives — Swierstra J et al., European Journal of Clinical Microbiology and Infectious Diseases 2016. (Review (gramicidin S - a distinct cyclic peptide))

Dosing context

Gramicidin appears only as a minor component of topical combination products applied to the skin or eye; there is no systemic dosing.

This is educational context only and not a usage recommendation.

Side effects & safety profile

Gramicidin is strongly hemolytic and toxic if administered systemically, which is why its use is restricted to topical and ophthalmic preparations, and even then at low concentrations within combination products.

Older studies characterized its hemolytic and antibacterial activity and its systemic toxicity.

Because it is never given systemically, safety concerns center on appropriate topical use.

Stacking & combinations

Gramicidin is almost always combined with neomycin and polymyxin B (and sometimes bacitracin) in topical and ophthalmic formulations so that the mixture covers both Gram-positive and Gram-negative organisms.

Finding Gramicidin vendors

User reviews

Frequently asked questions

References

1. [1] The gramicidin ion channel: a model membrane protein — Kelkar DA et al., Biochimica et Biophysica Acta 2007. PMID: 17572379. View sourceStudy: Review (mechanism)Reviewed the gramicidin cation channel as a model membrane protein, detailing its channel-forming mechanism.
2. [2] Gramicidin channels — Andersen OS et al., IEEE Transactions on Nanobioscience 2005. PMID: 15816168. View sourceStudy: Review (biophysics)Reviewed the biophysical behavior of gramicidin channels in lipid membranes.
3. [3] A randomized clinical trial of two topical preparations (framycitin/gramicidin and oxytetracycline/hydrocortisone with polymyxin B) in the treatment of external otitis — Wadsten CJ et al., Archives of Oto-Rhino-Laryngology 1985. PMID: 2415098. View sourceStudy: Randomized clinical trial (topical)Randomized trial comparing two topical preparations, one containing gramicidin, for external otitis.
4. [4] Gramicidin derivatives; toxicity; effect of proteins on hemolytic and bacteriostatic activity; antibacterial effect in vivo — Schales O et al., Archives of Biochemistry 1948. PMID: 18875044. View sourceStudy: Experimental (early antibacterial/toxicity)Early characterization of gramicidin derivatives' hemolytic and bacteriostatic activity and in vivo antibacterial effect.
5. [5] Gramicidin D enhances the antibacterial activity of fluoride — Nelson JW et al., Bioorganic and Medicinal Chemistry Letters 2014. PMID: 24857543. View sourceStudy: In-vitro (antibacterial)Showed that gramicidin D potentiates the antibacterial activity of fluoride, consistent with membrane permeabilization.
6. [6] Structure, toxicity and antibiotic activity of gramicidin S and derivatives — Swierstra J et al., European Journal of Clinical Microbiology and Infectious Diseases 2016. PMID: 26886453. View sourceStudy: Review (gramicidin S - a distinct cyclic peptide)Reviewed structure, toxicity, and antibiotic activity of gramicidin S and derivatives; included as related context, noting gramicidin S differs from linear gramicidin D.