Nafithromycin  (Synonyms: WCK 4873)

Nafithromycin (WCK 4873) is an orally active ketolide antibiotic with activity against Gram-positive bacteria, Gram-negative bacteria, and atypical respiratory pathogens (including drug-resistant strains). Nafithromycin binds to domains II and V of bacterial 23S rRNA and the peptidyl transferase center of the 50S ribosomal subunit, thereby inhibiting protein synthesis. Nafithromycin can be used in research related to bacterial infections^[1][2][3][4].

Nafithromycin (0.03-1 mg/liter; 72 h) exhibits in vitro activity against 10 clinical Chlamydia pneumoniae isolates, with an MIC₅₀ of 0.03 mg/liter and an MIC₉₀ of 0.25 mg/liter^[1].
Nafithromycin (WCK 4873) potently inhibits growth of erythromycin-sensitive, mef-expressing, ermB-expressing, and high-level ermB-expressing Streptococcus pneumoniae, as well as high-level ermB-expressing Streptococcus pyogenes, with MIC_s ranging from 0.015-0.03 μg/mL to 0.5 μg/mL^[2].
Nafithromycin shows non-cytotoxic effects up to 62.5 μg/mL in CHO cells, 31.25 μg/mL in MDBK, V79, HepG2, L929, and HeLa cells, and 15.6- ≤ 31.25 μg/mL in J774 cells^[2].
Nafithromycin exhibits potent in vitro activity against Streptococcus pneumoniae (MIC₅₀/MIC₉₀ 0.015/0.06 μg/mL, 100% inhibited at ≤0.25 μg/mL), Streptococcus pyogenes (MIC₅₀/MIC₉₀ 0.015/0.015 μg/mL, 100% inhibited at ≤0.5 μg/mL), and Moraxella catarrhalis (MIC₅₀/MIC₉₀ 0.12/0.25 μg/mL), bimodal activity against Staphylococcus aureus (MIC₅₀/MIC₉₀ 0.06/>2 μg/mL), and moderate activity against Haemophilus influenzae (MIC₅₀/MIC₉₀ 4/4 μg/mL) when tested against 2014 global clinical respiratory isolates via CLSI broth microdilution methods^[3].
Nafithromycin potently inhibits clinical Streptococcus pneumoniae isolates (including macrolide-resistant strains) with an MIC₅₀ of 0.03 mg/L and MIC₉₀ of 0.06 mg/L, and achieves 100% susceptibility at a PK/PD breakpoint of 0.25 mg/L^[4].
Nafithromycin potently inhibits Indian clinical Streptococcus pneumoniae isolates (including those with erm and mef-mediated macrolide resistance) with an MIC₅₀ of 0.015 mg/L and MIC₉₀ of 0.06 mg/L^[4].

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.

Nafithromycin exhibits systemic and hepatobiliary safety in repeat-dose toxicity studies in rats and dogs at exposures 3-8 fold higher than targeted therapeutic exposures^[2].

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.

859.04

C₄₂H₆₂N₆O₁₁S

1691240-78-4

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Room temperature in continental US; may vary elsewhere.

Please store the product under the recommended conditions in the Certificate of Analysis.

• [1]. Kohlhoff S. In Vitro Activity of Nafithromycin (WCK 4873) against Chlamydia pneumoniae. Antimicrob Agents Chemother. 2021 Aug 17;65(9):e0058521.

  [2]. Bhavsar S, et al. WCK 4873 (INN: Nafithromycin): Structure–activity relationship (SAR) identifying a novel lactone ketolide with activity against Streptococcus pneumoniae (SPN) and Streptococcus pyogenes (SPY). Results in Chemistry. 2023;5:100757.

  [3]. van der Meer JW, et al. Abstract!. The Netherlands journal of medicine. 2002 Dec;60(11):418.  [Content Brief]

  [4]. Kumar D, et al. Nafithromycin: a potential ketolide antibiotic for combating antimicrobial resistance in community-acquired bacterial pneumonia. Next Research. 2025;2(3):100592.