Gramicidin
One of the first antibiotics ever isolated, still found in eye and ear drops alongside neomycin and polymyxin B
Gramicidin punches channels through bacterial membranes and was isolated in 1939, before penicillin reached patients. It is too toxic to give by mouth or injection, so it survives only on the surface of the body, in eye and ear drops combined with other antibiotics. Its trials compare those combinations rather than gramicidin alone.
What is it?
Gramicidin is a short peptide made by soil bacteria. Two molecules stack end to end across a membrane to form a channel that lets sodium and potassium ions leak out, which kills bacteria. That channel is so well defined that biophysicists still use it as a model membrane protein, and a 2007 review describes it as the prototype ion channel.
The same action makes it toxic to human cells, including red blood cells, so it cannot be swallowed or injected. Its medical life is topical: drops that pair it with neomycin and polymyxin B, or with framycetin and dexamethasone, so the three antibiotics cover different bacteria.
The trials test those combinations. In bacterial conjunctivitis, neomycin-polymyxin-gramicidin drops matched trimethoprim-polymyxin in 48 patients. In acute external otitis, framycetin-gramicidin ear drops matched another combination, with 78% of 55 patients cured. In Aboriginal children with chronic suppurative otitis media, framycetin-gramicidin-dexamethasone did no better than ciprofloxacin, and discharge persisted in 70% either way.
After cataract surgery, drops containing gramicidin without a steroid controlled inflammation less well than steroid combinations, which is what they were included in that trial to show. Gramicidin is an antibiotic, not an anti-inflammatory.
At a Glance
Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Published Research
These are the studies that describe gramicidin, read from their PubMed abstracts: four randomised trials of combination drops and a review of its channel.
Bacterial conjunctivitis
48 patients were randomised, double-blind, to trimethoprim-polymyxin or neomycin-polymyxin-gramicidin eye drops. Both were very effective, with no difference in clearing organisms or clinical improvement and no adverse reactions with either.
Acute external otitis
55 patients took framycetin-gramicidin or oxytetracycline-hydrocortisone-polymyxin B ear drops for a week. 78% were cured, with no significant difference between the two preparations.
Chronic ear infection in children
97 Aboriginal children with persistent chronic suppurative otitis media were randomised to ciprofloxacin or framycetin-gramicidin-dexamethasone drops for 6 to 8 weeks. Discharge failed to resolve in 70% regardless of treatment.
After cataract surgery
271 patients took tobramycin-dexamethasone, dexamethasone-neomycin-polymyxin, or neomycin-polymyxin-gramicidin without a steroid for 21 days. Inflammation was significantly lower with the steroid combination than the gramicidin drops from day 8 on.
The model channel
A review of gramicidin as the prototype membrane ion channel, specific for monovalent cations, and what it has taught about how lipids and proteins interact in membranes.
Side Effects & Contraindications
Reported Side Effects
From the trials above.
Contraindications & Cautions
A topical antibiotic in prescription combinations.
Legal Status
Gramicidin is used only in combination topical products.
Frequently Asked Questions
?What is gramicidin?
A peptide antibiotic from soil bacteria that kills by forming channels through bacterial membranes. It was isolated in 1939.
?Why only in drops?
The same channel-forming action damages human cells, including red blood cells, so it cannot be swallowed or injected.
?Does it work?
In combination drops it matched other antibiotic combinations in conjunctivitis and external otitis trials.
?Is it an anti-inflammatory?
No. After cataract surgery, drops with gramicidin but no steroid controlled inflammation less well than steroid combinations.
References
- [pubmed] Genée E, et al. "Trimethoprim-polymyxin eye drops versus neomycin-polymyxin-gramicidin eye drops in the treatment of presumptive bacterial conjunctivitis - a double-blind study." Ophthalmologica, 1982;184(2):92-6. PMID: 6174913.
- [pubmed] Wadsten CJ, et al. "A randomized clinical trial of two topical preparations (framycitin/gramicidin and oxytetracycline/hydrocortisone with polymyxin B) in the treatment of external otitis." Arch Otorhinolaryngol, 1985;242(2):135-9. PMID: 2415098.
- [pubmed] Leach A, et al. "Topical ciprofloxin versus topical framycetin-gramicidin-dexamethasone in Australian aboriginal children with recently treated chronic suppurative otitis media: a randomized controlled trial." Pediatr Infect Dis J, 2008;27(8):692-8. PMID: 18664984.
- [pubmed] Notivol R, et al. "Comparison of topical tobramycin-dexamethasone with dexamethasone-neomycin-polymyxin and neomycin-polymyxin-gramicidin for control of inflammation after cataract surgery: results of a multicenter, prospective, three-arm, randomized, double-masked, controlled, parallel-group study." Clin Ther, 2004;26(8):1274-85. PMID: 15476908.
- [pubmed] Kelkar DA, et al. "The gramicidin ion channel: a model membrane protein." Biochim Biophys Acta, 2007;1768(9):2011-25. PMID: 17572379.
- [pubmed] Dubos RJ. "STUDIES ON A BACTERICIDAL AGENT EXTRACTED FROM A SOIL BACILLUS : I. PREPARATION OF THE AGENT. ITS ACTIVITY IN VITRO." J Exp Med, 1939;70(1):1-10. PMID: 19870884.
- [fda] US FDA, Drugs@FDA (openFDA): neomycin and polymyxin B sulfates and gramicidin ophthalmic solution, e.g. ANDA 064047 (Bausch and Lomb, prescription) and ANDA 065187 (prescription); several others discontinued. Read October 5, 2026.
Sources & Citations
Every study here was read from its PubMed record.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Consult a licensed healthcare provider before making health decisions.