Description

Azithromycin Dihydrate is a salt form of the active drug azithromycin. The term “dihydrate” indicates that each molecule of azithromycin is associated with two molecules of water (H2​O). This is a common way to formulate drugs for stability, manufacturing, and absorption. From a therapeutic standpoint, azithromycin dihydrate is the active pharmaceutical ingredient found in many azithromycin products (e.g., tablets and oral suspensions) and has the same clinical effects, indications, and mechanism of action as azithromycin. It is a macrolide antibiotic belonging to the azalide subclass, characterized by a 15-membered ring.

Indications

Azithromycin dihydrate is used to treat a broad range of bacterial infections. Its key features—such as its long half-life, high concentration in tissues, and ability to be administered in shorter courses—make it a common choice for various conditions. Indications include:

• Respiratory tract infections: Including community-acquired pneumonia, bronchitis, sinusitis, tonsillitis, and pharyngitis.
• Sexually transmitted infections (STIs): A single dose is highly effective for uncomplicated urethritis and cervicitis caused by Chlamydia trachomatis. It is also used for chancroid and sometimes for uncomplicated gonorrhea.
• Skin and soft tissue infections: Used for mild to moderate infections.

• Ear infections: A common treatment for acute otitis media.

• Prevention and treatment of Mycobacterium avium complex (MAC): Used in patients with advanced HIV/AIDS for both the treatment and prophylaxis of this type of lung infection.

• Other uses: Can also be used for conditions like traveler’s diarrhea and pertussis (whooping cough).

Mechanism of Action

The mechanism of action for azithromycin dihydrate is identical to that of azithromycin. It is a bactericidal agent that works by inhibiting bacterial protein synthesis. It does this by specifically targeting the bacterial ribosome, which is the cellular machinery responsible for creating new proteins. The process is as follows:

1. Binding to the 50S Ribosomal Subunit: Azithromycin dihydrate binds reversibly to the 23S ribosomal RNA (rRNA) of the 50S ribosomal subunit.

2. Inhibition of Translocation: By binding to this site, the drug blocks the process of “translocation,” which is the movement of the ribosome along the messenger RNA (mRNA) molecule. This movement is essential for adding new amino acids to the growing protein chain.
3. Cessation of Protein Synthesis: By preventing translocation, azithromycin dihydrate halts the elongation of the peptide chain. Without the ability to synthesize essential proteins, the bacteria cannot grow, reproduce, or perform basic functions, leading to their death or preventing their proliferation.

The drug’s effectiveness is further enhanced by its unique pharmacokinetic properties. It has a high affinity for and is actively absorbed by certain cells, particularly white blood cells like phagocytes. These cells then transport the drug to the site of infection, where it is released in high concentrations, leading to a potent and prolonged antibacterial effect.