Azithromycin Dihydrate

Product Story

Azithromycin was discovered in 1981 at the Pliva Research Institute in Zagreb, Croatia (then Yugoslavia), by a team led by Dr. Slobodan Đokić and including Gorjana Radobolja-Lazarevski and Zrinka Tamburašev. The team achieved a structural breakthrough that had eluded macrolide chemists for decades: they inserted a methyl-substituted nitrogen atom at position 9a of the erythromycin lactone ring, expanding it from a 14-membered to a 15-membered ring. This Beckmann rearrangement-derived structural modification created the first "azalide" — a new subclass of macrolide antibiotics. Pliva patented the compound in 1981 and later licensed it to Pfizer, which launched it globally as Zithromax in 1991. Azithromycin became one of the most commercially successful antibiotics in history, with peak annual sales exceeding $2 billion.

Azithromycin's mechanism follows the macrolide class pattern — binding to the 50S ribosomal subunit near the peptide exit tunnel to inhibit protein synthesis — but its pharmacokinetics are unprecedented. The 15-membered azalide ring confers exceptional acid stability (300-fold more stable than erythromycin at pH 2), enabling reliable oral absorption without protective formulation. More importantly, azithromycin exhibits a unique pharmacokinetic profile characterized by rapid and extensive tissue distribution followed by slow release, resulting in a terminal half-life of approximately 68 hours — the longest of any antibiotic in clinical use. This means a 3-day course provides 7-10 days of antimicrobial activity at the infection site, a paradigm shift from traditional multi-week antibiotic regimens. Azithromycin is actively concentrated within phagocytes (achieving intracellular concentrations 100-200x serum levels), which transport it to sites of infection.

Azithromycin's clinical advantages are threefold: (1) short-course therapy (3-5 days vs. 7-14 days for comparators), dramatically improving patient compliance; (2) once-daily dosing enabled by the long half-life; and (3) a favorable safety profile with minimal drug-drug interactions (unlike clarithromycin, azithromycin does not inhibit CYP3A4). The single 1g oral dose regimen for uncomplicated Chlamydia trachomatis infection is a landmark in STD treatment — it effectively eliminated non-compliance as a cause of treatment failure. Beyond its antibacterial role, azithromycin has immunomodulatory and anti-inflammatory properties that are exploited in the long-term management of cystic fibrosis and diffuse panbronchiolitis, and it is used in mass drug administration programs for trachoma control in endemic regions.

As of mid-2026, global azithromycin API demand exceeds 2,000 metric tons annually. The market has been competitive since Pfizer's basic patent expired in 2005 (US) and 2008 (EU). China and India dominate production, with Chinese manufacturers controlling the erythromycin A fermentation and semi-synthetic conversion chain. The COVID-19 pandemic created a demand spike in 2020 due to its investigation as a potential therapy, but volumes have since normalized. Azithromycin is listed on the WHO Model List of Essential Medicines. KingWish supplies GMP-certified azithromycin dihydrate meeting USP/EP/CP standards, with consistent particle size distribution and polymorphic form for reliable formulation performance.

Quality Specifications

Therapeutic Applications

• Community-acquired pneumonia: First-line oral macrolide (500 mg day 1, then 250 mg days 2-5) for CAP caused by S. pneumoniae, H. influenzae, and atypical pathogens including Legionella pneumophila.
• Upper respiratory tract infections: 5-day azithromycin course (Z-pack) for pharyngitis, tonsillitis, acute sinusitis, and acute otitis media. Equivalent efficacy to 10-day penicillin/amoxicillin with superior compliance.
• Chlamydia trachomatis: Single 1g oral dose for uncomplicated urogenital chlamydia — the landmark regimen that redefined compliance-driven STD treatment. Also effective for chancroid and non-gonococcal urethritis.
• Skin and soft tissue infections: Effective for mild uncomplicated skin infections caused by S. aureus and S. pyogenes. Once-daily dosing improves adherence in community settings.
• Mycobacterium avium complex (MAC): Prophylaxis (1,200 mg weekly) against disseminated MAC in HIV patients with CD4 <50 cells/mm3. Also used in combination therapy for MAC pulmonary disease.