Description

Azithromycin is a macrolide antibiotic that is a semi-synthetic derivative of erythromycin. It is a broad-spectrum, bactericidal agent known for its ability to penetrate and accumulate in body tissues, particularly in immune cells like macrophages. This characteristic, combined with its long half-life, allows for shorter treatment courses (e.g., a one-time dose or a 5-day course) compared to many other antibiotics. It is available in various forms, including tablets, capsules, and oral suspension.

Indications

Azithromycin is used to treat a wide range of bacterial infections. Its long-lasting effect and ability to target specific types of bacteria make it a popular choice for many conditions. Key indications for azithromycin include:

• Respiratory tract infections: This includes community-acquired pneumonia, bronchitis, sinusitis, tonsillitis, and pharyngitis (strep throat).

• Sexually transmitted infections (STIs): It is highly effective as a single dose for treating uncomplicated urethritis and cervicitis caused by Chlamydia trachomatis. It is also used to treat chancroid and sometimes for gonorrhea.

• Skin and soft tissue infections: It is used for uncomplicated infections caused by susceptible organisms.

• Ear infections: It is a common treatment for acute otitis media.

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

• Other uses: It can also be used for conditions like traveler’s diarrhea, Lyme disease, and pertussis (whooping cough).

Mechanism of Action

Azithromycin works by inhibiting the synthesis of essential proteins within bacterial cells. Its mechanism is similar to other macrolide antibiotics and involves a specific interaction with the bacterial ribosome:

1. Binding to the 50S Ribosomal Subunit: Azithromycin binds reversibly to the 23S ribosomal RNA (rRNA) within the 50S subunit of the bacterial ribosome. This is the part of the bacterial protein-making machinery that assembles amino acids into a polypeptide chain.
2. Inhibition of Translocation: By binding to this specific site, azithromycin blocks the “translocation” step of protein synthesis. Translocation is the process where the ribosome moves along the messenger RNA (mRNA) molecule to add a new amino acid.
3. Cessation of Protein Synthesis: This blockage prevents the elongation of the growing peptide chain. Without the ability to synthesize new proteins, the bacteria cannot grow, reproduce, or repair themselves, which ultimately leads to their death or prevents their proliferation.

Azithromycin’s effectiveness is also enhanced by its unique pharmacokinetic properties. It is highly concentrated in white blood cells, such as phagocytes, which then transport the drug directly to the site of infection. This “targeted delivery” mechanism allows the drug to accumulate in infected tissues at concentrations much higher than in the blood, leading to a potent and prolonged antibacterial effect.