What it is
Acetic acid is the acid that gives vinegar its sour taste and sharp smell. Household vinegar is roughly 5 to 8% acetic acid in water. At full strength, called glacial acetic acid, it is a corrosive and flammable chemical that burns skin and eyes.
This article is about dilute acetic acid as it appears in peptide chemistry, where it turns up in two ways. First, most approved peptide medicines are made as “acetate salts”: each peptide molecule is paired with acetate, the charged form of acetic acid, an ion regarded as milder and less likely to interfere with biological testing than the alternatives left over from manufacture. Second, in research laboratories dilute acetic acid is one of the standard solvents for getting certain peptides into solution for analysis.
It is not a drug for injection, and no FDA-approved product uses it as a peptide solvent.
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
Nobody invented acetic acid. People have made vinegar by fermenting wine and other alcoholic liquids for thousands of years, and acetic acid is the active component. Today it is also produced industrially on a very large scale.
Its role in peptide medicine is more recent. As synthetic peptide drugs multiplied, acetate became the usual partner ion for the finished medicine; a 2020 review found that most approved peptide drugs are acetate salts, including leuprolide and oxytocin. The FDA label of the bone drug teriparatide lists glacial acetic acid and sodium acetate among its inactive ingredients.
In medicine, acetic acid itself has been sold for decades as ear drops and as a weak bladder-rinse solution.
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
There are no efficacy trials of dilute acetic acid as a laboratory solvent, and none would make sense. A solvent is a tool for chemistry, not a treatment. Clinical research on acetic acid’s own medical uses, such as ear infections, is outside the scope of this page.
What exists instead is safety information. The approved ear drops can sting or burn briefly in an inflamed ear and are not used when the eardrum is perforated. The approved bladder rinse is labelled not for injection, and its label reports body-wide acid build-up, pain and blood in the urine in some patients. For the chemical itself, occupational safety agencies set limits on breathing its vapour, and the concentrated form causes serious burns. How hazardous a solution is depends heavily on its strength.
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
Several FDA-approved products contain acetic acid as their active ingredient: 2% ear drops, first approved in 1960, and a 0.25% bladder irrigation, approved in 1979. Under this site’s definitions that makes its approval status “approved”. None of those approvals covers injection, and the irrigation label says outright that it is not for injection.
No FDA-approved product uses dilute acetic acid as a solvent for dissolving peptides, and nothing in those approvals extends to that use. Its presence as an acetate salt or buffer in approved peptide drugs is part of each finished product’s own approval, not a separate approval of acetic acid.
Pharmacy compounding rules for bulk drug substances are not applied on this page, which treats acetic acid as a laboratory supply.
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.
