Zithromax (Azithromycin): How It Works, Application, Side effects

Zithromax (azithromycin) is applied for, among other uses, to treat infections of the airways and skin, including acne and erythema. The medicine is also applied for the treatment of UTIs and cervical mucositis triggred by Chlamidia infection, as well as a host of other STIs. The drug is available in form of eye drops applied in patients with Chlamydia-triggered conjunctivitis and trachomatous conjunctivitis.


How does Zithromax work?

Zithromax is a drug from the group of macrolide antibiotics. They are characterized by a complex chemical structure. The first drugs in this group were isolated from the Streptomyces species, and are now produced synthetically. Macrolide antibiotics work by inhibiting bacterial protein synthesis in the process of RNA chain extension (binding to the 50S ribosome subunit). This mechanism indicates their bacteriostatic effect.

Azithromycin is a derivative of erythromycin. The mechanism of action of macrolide antibiotics is based on inhibition of protein biosynthesis in bacterial cells by binding to the 50S ribosomal subunit and disrupting the elongation of the protein chain (the ribosome is an element of the cell serving for the production of proteins, composed of two subunits – large 50S and small 30S). Since cell growth is inhibited rather than being killed, we say that macrolides are bacteriostatic antibiotics. They are characterized by a broad spectrum of activity, i.e. they are active against many species of bacteria. In respiratory infections, macrolides are considered as an alternative to β-lactam antibiotics.

In order for an antibiotic to work effectively, it must reach the concentration at the site of infection necessary to inhibit the growth or kill the pathogenic microorganism, and at the same time that concentration must remain safe for human cells. If both of these conditions are met, we say the microorganism is antibiotic sensitive, if not, we say antibiotic resistance. Antibiotic resistance can be innate or acquired as a result of genetic mutation in bacteria and selection of resistant strains, or through the transfer of resistance genes between bacterial cells (this is called horizontal transfer). Resistance to macrolide antibiotics can arise from active drug clearance, production of ribosomal proteins to displace the drug from association with the 50S subunit, enzymatic inactivation, or by chromosomal mutations that alter the 50S protein.

Effects duration

After oral administration, azithromycin is well absorbed from the gastrointestinal tract, the maximum concentration in the blood is reached after 2-3 hours. The biological half-life of azithromycin is long and amounts to 2-4 days, therefore it can be taken once a day for 1-5 days. Azithromycin is mainly eliminated in the bile as unchanged drug and as metabolites. After administration into the conjunctival sac, it is not found in the blood.


The undesirable effects that may occur after the use of macrolide antibiotics are gastrointestinal symptoms such as nausea, vomiting, loose stools, diarrhea. They are usually mild and often disappear during or after treatment. It may also be beneficial to take preparations that restore the normal composition of the intestinal flora.

Zithromax is active against the following bacteria:

  • pneumoniae,
  • Ureaplasma,
  • Chlamydia,
  • Legionella,
  • Gram-positive cocci Streptococcus,
  • Gram-negative cocci Moraxella,
  • influenzae,
  • Bordetella petrussis,
  • Camphylobacter,
  • Helicobacter
  • Corynebacterium diphteriae,
  • Mycobacterium avium complex,
  • Clostridium, Listeria.
  • Female health conditions
  • For signs of infection in adults
  • Pain and fever
  • Runny nose and sinuses
  • Otitis
  • Sore throat
  • Cough

The antibiotic has no effect on P. aerguinosa, Enterococcus, Nocardia and MRSA.

Zithromax is used in bacterial infections in which the bacteria are sensitive to the active substance.

Those are:

  • Upper respiratory tract infections – inflammation of the throat, sinuses, tonsils;
  • Acute otitis media;
  • Lower respiratory tract infections – acute bronchitis, exacerbation of chronic bronchitis, pneumonia (mild to moderately severe);
  • Skin and soft tissue infections – erysipelas, impetigo, secondary pyoderma;
  • Wandering erythema.
  • Skin irritations

Dosage and posology

Zithromax is administered orally in the form of tablets or a suspension. Usually doses of 0.5-1 g / day are used. It is very well absorbed when taken with a meal. It penetrates well into the tissues and achieves a high concentration there, so a shorter therapy lasting 3-5 days is possible. The elimination of the drug from the body is mainly via the bile or via the faeces.


The drug should not be used in case of allergy to the active substance or any of the excipients. Caution should be exercised when taking Zithromax in diseases associated with cardiac arrhythmias, as it prolongs the period of cardiac repolarization. The substance may interact with other drugs, but due to its structure it has a lower interaction potential than the rest of macrolides.

Be careful and tell your doctor about the following medications:

  • pimozide, astemizole, terfenadine – risk of QT prolongation;
  • ergotamines, dihydroergotamines – possible vasospasms and limb ischemia;
  • HMG-CoA reductase inhibitors (simvastatin, lovastatin) – risk of rhabdomyolysis;
  • oral antidiabetic drugs – possibility of hypoglycaemia;
  • oral anticoagulants – risk of bleeding.

The drug can be used during pregnancy and breastfeeding only when necessary, because the substance crosses the placenta and into breast milk.

Side effects

Zithromax is well tolerated with few side effects.

The most common are:

  • Dizziness,
  • Somnolence,
  • Headaches,
  • Taste disturbance
  • Smell,
  • Nausea,
  • Vomiting,
  • Diarrhea,
  • Stomach pain,
  • Allergic reactions
  • Palpitations,
  • Arrhythmias.

Zithromax is a substance used to treat i.a. upper and lower respiratory tract and skin infections. Due to the short therapy and the wide spectrum of action, it is often prescribed by doctors.

Important note:

This patient information is published for educational purposes only. The instructions and product properties quoted on this page follow the guidelines outlines by the drug manufacturer, but do not replicate it in all fullness. We strongly advise against using this information as a call to action of any kind, be it purchasing or using the drug without a proper medical consultation carried out first. Trademarks, names of companies and eventual studies are inserted for informational purposes and as a legal reference and respect for the copyright law and ethics.