What it is
Acetic acid is the acid in vinegar. It gives vinegar its sour taste and sharp smell. Household vinegar is roughly 5 to 8% acetic acid in water. The full-strength form is called glacial acetic acid. It can burn skin and eyes, and it can catch fire.
This page is about weak (dilute) acetic acid in peptide work. A peptide is a short chain of amino acids. Acetic acid shows up in two ways.
First, most approved peptide medicines are made as “acetate salts”. Acetate is the charged form of acetic acid. It is paired with each peptide molecule. It is seen as milder than other partners left over from manufacturing. It is also less likely to upset lab tests.
Second, labs use weak acetic acid to dissolve some peptides for testing.
It is not a drug for injection. No FDA-approved product uses it to dissolve peptides.
Acetic acid (ethanoic acid, CH3COOH, C2H4O2, 60.05 g/mol, CAS 64-19-7) is a weak carboxylic acid with a pKa of 4.76 at 25 °C, fully miscible with water. Below its pKa it exists mainly in the protonated form; above it, mainly as acetate.
In peptide chemistry its relevance is as a counter-ion and a solvent. Peptides made by solid-phase synthesis are cleaved from the resin and purified with trifluoroacetic acid (TFA), so cationic peptides are first obtained as TFA salts. Because TFA can interfere biologically and analytically, pharmaceutical peptides are usually converted to other salts; a 2020 review by Sikora and colleagues states that most approved peptide pharmaceuticals are acetate salts, with conversion done by ion-exchange resins or repeated lyophilisation. The same review lists acetic acid, at about 0.1% (v/v), among routine acidic mobile-phase additives in peptide HPLC. As a solvent, dilute acetic acid protonates basic side chains (lysine, arginine, histidine) and the N-terminus, increasing net positive charge and aqueous solubility of basic peptides. Acetic acid and acetate also serve as a buffer pair in some approved peptide injections.
Who made it and when
No one invented acetic acid. People have made vinegar for thousands of years. They did it by letting wine and other alcoholic drinks turn sour. Acetic acid is the part of vinegar that does the work. Today factories also make it in very large amounts.
Its role in peptide medicine is newer. As more man-made peptide drugs appeared, acetate became their usual partner. A 2020 review found that most approved peptide drugs are acetate salts. Examples include leuprolide and oxytocin. The FDA label of the bone drug teriparatide lists glacial acetic acid and sodium acetate as inactive ingredients.
Acetic acid has also been sold as a medicine for decades. It comes as ear drops and as a weak rinse for the bladder.
The approved medical products containing acetic acid as the active ingredient are old ones. VoSol, a 2% acetic acid otic solution, was approved under NDA 012179 on 17 May 1960; it is now discontinued, and FDA has determined it was not withdrawn for reasons of safety or effectiveness. Generic 2% acetic acid otic solutions remain on the market, for example ANDA 040607, approved in 2005; one current DailyMed label describes such a product as a non-aqueous solution in propylene glycol with benzethonium chloride and propylene glycol diacetate. B. Braun’s 0.25% Acetic Acid Irrigation was approved under NDA 018161 on 6 August 1979; it is hypotonic (42 mOsmol/L) with a pH of about 3.1 and is labelled not for injection.
As an excipient, acetic acid appears in approved peptide injections as part of an acetate buffer. The current Forteo (teriparatide) label, revised August 2026, lists 0.41 mg/mL glacial acetic acid and 0.1 mg/mL sodium acetate, with pH adjusted to 4. The Sikora review tabulates approved peptides by counter-ion, listing acetate salts such as leuprolide, oxytocin, liraglutide and enfuvirtide, with trifluoroacetate (bivalirudin, corticorelin) and chloride (glucagon, gramicidin D) as exceptions.
What the data say
No studies test how well weak acetic acid works as a lab solvent (something that dissolves things). Such studies would not make sense. A solvent is a chemistry tool, not a treatment. Studies of acetic acid for ear infections are not covered on this page.
What exists instead is safety information:
- The approved ear drops can sting or burn for a short time in a sore, swollen ear.
- The ear drops are not used if the eardrum has a hole in it.
- The approved bladder rinse is labelled not for injection.
- Its label reports too much acid in the body, pain, and blood in the urine in some patients.
- Workplace safety agencies set limits on how much of its vapour people can breathe.
- The full-strength form causes serious burns.
How dangerous a solution is depends a lot on how strong it is.
No efficacy trials exist for acetic acid as a solvent or counter-ion, because these are chemical functions with no therapeutic claim. The safety evidence comes from approved product labels and occupational hazard data.
Otic 2% solution (label): occasional stinging or burning on application to an inflamed ear; perforated tympanic membrane is a contraindication; safety has not been established below 3 years of age. Irrigation 0.25% (label): use with mucosal lesions of the bladder may be harmful, absorption through open lesions may cause systemic acidosis, and systemic acidosis, pain and haematuria have been reported; the antimicrobial effect depends on maintaining an effluent pH of 5.0 or lower. Occupational data (NIOSH): REL 10 ppm TWA and 15 ppm STEL, OSHA PEL 10 ppm, IDLH 50 ppm, flash point of the glacial acid 103 °F. GHS notifications compiled in PubChem classify the pure substance as Flam. Liq. 3 (H226) and Skin Corr. 1A (H314). Under the EU harmonised entry, the skin category steps down with dilution: corrosive 1A at 90% or above, corrosive 1B from 25% to under 90%, and irritant category 2 from 10% to under 25%.
Regulatory picture
The FDA has approved some products with acetic acid as the active ingredient. These are 2% ear drops, first approved in 1960, and a 0.25% bladder rinse, approved in 1979. By this site’s rules, that makes its status “approved”.
None of these approvals covers injection. The bladder rinse label clearly says it is not for injection.
No FDA-approved product uses weak acetic acid to dissolve peptides. The approvals above do not cover that use. Some approved peptide drugs contain acetate as a salt or as a buffer (an ingredient that keeps the acid level steady). That is part of each drug’s own approval. It is not a separate approval of acetic acid.
This page treats acetic acid as a lab supply. So pharmacy compounding rules (rules for mixing custom medicines) are not applied here.
The approval field is set to approved because FDA-approved products contain this exact molecule as the active ingredient: VoSol (NDA 012179, 1960; discontinued), generic acetic acid otic solution 2% (for example ANDA 040607, 2005) and 0.25% Acetic Acid Irrigation (NDA 018161, 1979). Their indications are superficial infections of the external auditory canal and bladder irrigation in patients with prolonged indwelling urethral catheters. No approved acetic acid product is labelled for parenteral use, and none is labelled as a solvent for peptides or other drugs.
Where acetic acid or acetate appears in approved peptide injections, it does so as a counter-ion or buffer component reviewed within that product’s application and controlled by its specifications. The compounding field is recorded as not applicable, consistent with this site’s treatment of supplies. Laboratory handling guidance, such as that published by the UK’s NIBSC for its peptide reference materials, describes dilute acetic acid as an option for dissolving basic, positively charged peptides for research use; that is laboratory practice and has no bearing on use in people or animals.
