Framycetin Sulfate vs Neomycin Sulfate: What API Buyers Need to Check Before Ordering

Framycetin sulfate (CAS 4146-30-9) is the sulfate salt of neomycin B — a purified single-entity aminoglycoside, distinct from the variable neomycin B/C/neamine mixture sold as neomycin sulfate (CAS 1405-10-3). The two are not interchangeable in a dossier. Buyers selecting material for topical, ophthalmic, aural or nasal formulations should verify four things before ordering: the CAS number, the applicable monograph, the neomycin C limit, and whether potency is expressed against neomycin B on the dried substance.

What is framycetin sulfate?

    Framycetin sulfate is the sulfate salt of neomycin B, an aminoglycoside antibiotic produced by selected strains of Streptomyces fradiae or Streptomyces decaris. Its chemical formula is C₂₃H₄₆N₆O₁₃·xH₂SO₄ (base MW 615), its CAS number is 4146-30-9, and its ATC codes are D09AA01 (topical), R01AX08 (nasal) and S01AA07 (ophthalmic).

It appears as a white to yellowish-white hygroscopic powder, freely soluble in water, very slightly soluble in alcohol and practically insoluble in acetone.

How does framycetin sulfate differ from neomycin sulfate?

    Framycetin sulfate is purified neomycin B with pharmacopoeially controlled limits on neomycin C and neamine; neomycin sulfate is a variable mixture of all three components. This is a compositional distinction, and it is what determines whether antimicrobial performance is reproducible from batch to batch.

    Supplier and aminoglycoside literature reports neomycin B as roughly 65% more active than neomycin C and about 90% more active than neomycin A. We cite this as reported literature, not as a clinical superiority claim.

Why the CAS number alone is not enough？

    Two materials can share a neomycin lineage and still sit under different monographs. Always cross-check CAS number, monograph and impurity limits together — a supplier quoting "neomycin" without specifying which substance is a procurement risk.

How does framycetin sulfate work?

    Framycetin binds the 30S ribosomal subunit — specifically the 16S rRNA and the S12 protein — blocking mRNA reading, inducing misreading and translational frameshift, and causing premature termination. The effect is bactericidal rather than bacteriostatic, which is the clinically relevant property where bacterial load must be reduced quickly.

What is framycetin sulfate used for?

    Framycetin sulfate is used topically at 1% for skin infections and at 0.5% for eye and ear infections, often combined with other antibacterials or corticosteroids.It is active against staphylococci (including strains resistant to other antibiotics), Pseudomonas aeruginosa, coliform bacteria and pneumococci.

Regulatory product information for ophthalmic framycetin preparations notes that the substance is exceptionally well tolerated by ocular tissues and that the preparations are non-irritant— a relevant consideration when selecting among aminoglycosides for ophthalmic use.

Which specification parameters should buyers check before ordering?

    Check six parameters beyond the headline assay: potency basis (IU/mg on dried substance), neomycin C content, neamine content, pH, specific optical rotation, and loss on drying.Two additional items — microbial limits and particle size distribution — are not required by the monograph but materially affect formulation behaviour.

Why is composition control the real differentiator?

    Because two suppliers can both write "complies" while delivering material with very different stereochemical profiles, potency headroom and microbial burden.Those differences surface downstream as MIC variability, preservative-efficacy failures, or out-of-specification results at the end of shelf life — not as a line item on an incoming-goods check.

Asking for the measured value rather than the pass/fail statement is the single most effective qualification step a buyer can take.

FAQ

1. Is framycetin sulfate the same as neomycin sulfate?

No. Framycetin sulfate (CAS 4146-30-9) is purified neomycin B with neomycin C limited to 3%. Neomycin sulfate (CAS 1405-10-3) is a variable mixture of neomycin B, neomycin C and neamine.

2. What is the CAS number of framycetin sulfate?

4146-30-9. The free base framycetin is CAS 119-04-0.

3. What potency does Ph. Eur. require?

A minimum of 630 IU/mg, calculated with reference to the dried substance.

4. Is framycetin sulfate used systemically?

No. It is not used systemically because of aminoglycoside nephrotoxicity and ototoxicity, and it is poorly absorbed from the gastrointestinal tract.

5. What concentrations are used in finished products?

1% for skin cream and ointment, 0.5% for eye and ear preparations.