Gramicidin

gramicidin D (Dubos; mixture of gramicidins A/B/C), gramicidin A; component of tyrothricin; distinct from gramicidin S (a separate cyclic peptide)

Antimicrobial & antiviral

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1What it is

Gramicidin is one of the first antibiotics ever used clinically. It was found by René Dubos in 1939 in the soil bacterium Brevibacillus brevis, as part of a mixture called tyrothricin. Gramicidin D ("D" for Dubos) is actually a blend of closely related linear 15-amino-acid peptides (gramicidins A, B and C). It should not be confused with gramicidin S, an unrelated cyclic peptide.

Because it damages human cells as well as bacteria, gramicidin is used only topically — most familiarly as a component of combination eye drops (with neomycin and polymyxin B) and in some skin preparations and throat lozenges. It is an approved pharmaceutical ingredient, not a community research peptide.

2How it's thought to work

Gramicidin's 15-residue chain folds so that two molecules join head-to-head and span the membrane, creating a channel. Through this channel, monovalent cations such as sodium and potassium flow freely, wrecking the bacterium's carefully maintained ion gradients. In bacteria this quickly stops the processes that depend on those gradients, including energy production. The same channel-forming action damages human cell membranes and mitochondria, which is why it cannot be given internally.

A channel-forming peptide that threads the membrane and lets sodium and potassium leak through. Topical only: it destroys red blood cells if it reaches the bloodstream.Schematic — not to scale

3What the research shows

Graded A (by long clinical use)

Topical antibacterial use

Gramicidin has been a component of approved topical antibacterials for decades, chiefly in ophthalmic combinations (for example with neomycin and polymyxin B for superficial bacterial eye infections) and in skin and throat preparations. Its effectiveness against Gram-positive bacteria in these settings is well established through long use and the approval of the finished products.

Not gradedfoundational science

Channel biophysics

Gramicidin A is one of the most studied model ion channels in all of biophysics; its structure and conductance have taught much about how peptides form membrane pores. This is basic science rather than a clinical grade.

Not gradedruled out

Systemic use

Early attempts at systemic use were abandoned because gramicidin lyses red blood cells and is toxic to liver, kidney and other tissues. This is settled and is the reason for the topical-only restriction.

4Reported side effects and interactions

Literature-reported

Topically, gramicidin-containing products are generally well tolerated; local irritation or allergic reaction can occur, as with any topical antibiotic. Systemic use causes haemolysis and organ toxicity and is not done.

Community-reported

Community use: essentially none documented beyond ordinary use of approved topical products. It is not a self-injected peptide.

Theoretical. the overriding issue is intrinsic toxicity to human cells, which confines it to the skin and eye surface.

Interactions. in combination products, the relevant profile is that of the whole formulation (e.g. neomycin sensitisation).

Markers researchers commonly monitor

Not applicable — topical use at the eye or skin surface needs no blood monitoring, and systemic use does not occur. The historical reason for avoiding systemic use (haemolysis, organ toxicity) is the context in which markers like red-cell indices and liver/kidney function would ever have mattered.

Free for everyone. Safety information is never behind a paywall.

5Formulation and handling

Used as a low-concentration ingredient in finished topical/ophthalmic products; not supplied as a peptide for . No calculator link applies.

6Commonly studied alongside

Neomycin and Polymyxin B and Colistin (its usual partners in eye/skin combinations), tyrocidine (the other half of tyrothricin), bacitracin.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Approved ingredient in topical/ophthalmic combination products (e.g. neomycin–polymyxin B–gramicidin eye drops)
European Union	Approved in topical combination products
United Kingdom	Licensed in topical/ophthalmic combinations
Australia	Approved in topical combination products
South Africa	Available in registered topical combinations
Sport	Not listed by WADA; not a performance substance

8Open questions

Can gramicidin's channel chemistry inspire safer, more selective membrane-active antibiotics?
Is there any way to target it so that systemic use becomes possible, or is the host-cell toxicity fundamental?

9References

1Dubos RJ (1939). Studies on a bactericidal agent extracted from a soil bacillus. J Exp Med. PubMed · DOI
2Kelkar DA, Chattopadhyay A (2007). The gramicidin ion channel: a model membrane protein. Biochim Biophys Acta. PubMed · DOI
3Wallace BA (1990). Gramicidin channels and pores. Annu Rev Biophys Biophys Chem. PubMed · DOI
4Product labelling for neomycin–polymyxin B–gramicidin ophthalmic solution (current). PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

10Community

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Self-reported side effects Phase 2

Not enough data yet. 0 of the 50 members needed have logged this compound for 4+ weeks. We don't show anything below 50, so no one can be identified.

11Page history

30 Oct 2026Profile published — awaiting medical review

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