Azithromycin: Formula, Indications, Mechanism of Action, Dosage, Warnings, Contraindications and Interactions

It is a drug with antibiotic properties that correspond to the group of azalides, which is derived from the macrolides.

This component is active against a moderately extensive group of bacteria analogous to those that respond to the action of penicillins.

So patients allergic to penicillins can use azithromycin as an alternative treatment.

Chemical formula

  • C38H72N2O12.


Azithromycin Hydrochloride:

  • 500 mg coated tablets.
  • Powder for suspension 200 mg per 5 ml once the mixture is made.
  • 500 mg injections in each ampoule of 5 ml.


In tablets and suspension, it is indicated in:

Infections of the lower respiratory tract such as chronic bronchitis and pneumonia.

Soft tissue and skin infections that may have mild to moderate severity, uncomplicated cervicitis, and urethritis are caused by Chlamydia trachomatis.

Upper respiratory tract infections include acute bacterial sinusitis, pharyngotonsillitis, acute otitis media, and other conditions caused by susceptible organisms.

In sexually transmitted infections, azithromycin is indicated in both men and women in the therapies of uncomplicated genital infections caused by Chlamydia trachomatis and Neisseria gonorrhoeae.


The concomitant infection with Treponema pallidum should not be included in the indications.


In cases of pneumonia caused by sensitive microorganisms in the particular case of hospitalized immunocompetent adult patients.

The administration of azithromycin in this type of patient could be carried out concomitantly with other antibiotics as in the cases of pelvic inflammatory diseases caused by:

Chlamydia trachomatis, Neisseria gonorrhoeae, and Mycoplasma hominis in the cases of patients requiring an initial intravenous therapy.

In cases where an infection caused by anaerobic microorganisms is suspected, the anaerobicidal antimicrobial agent should be administered concomitantly with azithromycin.

Injectable azithromycin is usually a continuation of oral treatment.

Mechanism of action

Azithromycin inhibits the growth of bacterial organisms because it hinders the production of bacterial proteins essential for its multiplication and division.

This is because it binds irreversibly to the 50s subunit found in the ribosome of the bacterium and also differs. After all, it does not allow the translocation of the peptides.


This drug can be administered orally and intravenously.

In the case of oral tablet administration, absorption of the drug is rapid. It has a bioavailability of approximately 37%, so that it can be affected by joint ingestion of food.

Therefore, it is recommended to administer 1 or 2 hours before each meal.

In the case of its use in suspension, it has a much faster absorption, up to 55%, without it being able to modify its bioavailability.

The treatment administration time will depend on the pathology and the degree of infection, usually indicated for 1 to 5 days.

In the case of using azithromycin for suspension, it is essential to dissolve the content in water, mix well, take all the content entirely, and consume before 12 hours after dissolution.

In adults and for the treatment of sexually transmitted diseases caused by Chlamydia trachomatis, Haemophilus ducreyi, or some susceptible strains of Neisseria gonorrhoeae.

The dose of azithromycin is 1 g in a single dose; in the elderly, the same amount is used as in adults.

In patients with mild to moderate renal impairment, a glomerular filtration rate of 10-80 ml/min or a severe glomerular filtration rate of less than 10 ml/min and no dose adjustment is necessary.

Azithromycin is usually prescribed as a treatment for 3 or 5 days.

If the treatment is three days, 500 mg daily should be administered.

If the treatment is for five days, an initial dose of 500 mg is recommended, and continue with 250 mg daily for the next four days.

The recommended treatment should be administered until the end since its interruption before time can cause the infection to reappear.

Side effects

Among the side effects have been reported:

  • Difficulty breathing, an irregular heartbeat, and as a consequence, excessive tiredness.
  • Loss of appetite, lack of energy, and possible fainting.
  • Skin symptoms have been noted as itching, hives, fever, scaling, sores like blisters full of pus (lesions), swollen and reddened areas, unusual bruising, and jaundice on the skin and eyes.
  • Severe diarrhea can occur in liquid or blood, which may be accompanied or not accompanied by fever or stomach cramps that may occur for more than two months after the end of treatment.
  • Dark-colored urine, nausea, and vomiting also occur.
  • Irritability may occur in infants less than six weeks of age while feeding.
  • The presence of unusual muscle weakness or difficulty controlling muscles.
  • Swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, lower legs, and hoarseness may occur.
  • Pains in the upper right part of the stomach.
  • Headaches.

Intravenously, reactions include anorexia, pain, inflammation in the injection area, paresthesia, rashes, visual disturbances, pruritus, dizziness, deafness, dysgeusia, vomiting, flatulence, dyspepsia, arthralgia, and fatigue can be experienced.

A decrease in the lymphocyte count and the blood bicarbonate in the laboratory and an increase in eosinophils, basophils, monocytes, and neutrophils can occur.

These side effects can be aggravated. If you experience these symptoms, you should stop azithromycin immediately and seek emergency medical treatment.

Warnings and contraindications

It should not be administered in cases of hypersensitivity to azithromycin, erythromycin, or any other macrolide or ketolide antibiotic.

In the case of significant liver diseases, liver function tests should be monitored, and if signs or symptoms of hepatic dysfunction or failure appear, treatment should be discontinued.

There is a risk of diarrhea related to Clostridium difficile and superinfection due to non-sensitive microorganisms of fungal type.

Particular caution should be exercised in patients with arrhythmogenic diseases in progress, especially in female patients and the elderly.

In cases with the existence of electrocardiogram charts with prolongation of the congenital or confirmed QT interval, concomitant administration with QT interval prolonging drugs.

As well as antiarrhythmics such as quinidine and procainamide, dofetilide, amiodarone, and sotalol.

Avoid concomitant administration with medications such as terfenadine, cisapride, pimozide, citalopram, moxifloxacin, and levofloxacin.

Its use should be avoided in cases of electrolyte disturbance, particular hypokalemia or hypomagnesemia, clinically relevant bradycardia, arrhythmia, severe heart failure, in cases of risk of exacerbation or the appearance of myasthenia gravis.

It is not considered an empirical treatment of the first choice in cases of infections in those areas where the permanence of the resistant strains is more excellent than or equal to 10%.

Nor is it the first treatment choice to combat pharyngitis or tonsillitis caused by infection with Streptococcus pyogenes.

It is also not recommended to treat infected burns; a preliminary sensitivity analysis should be performed for soft tissue infection treatments.

In the case of pregnant women, administer if the benefit compensates the risk since adequate investigations are not available during pregnancy.

In animal reproduction studies, it has been reported that it passes through the placenta, so its safety is not established.

Azithromycin is excreted through breast milk, but it is unknown if it can cause adverse reactions in the infant.

Therefore, it is recommended to interrupt breastfeeding while administering azithromycin treatment.

The possible consequences for the infant are diarrhea, fungal infections in the mucous membranes, and sensitization.

It is advisable to discard the breast milk during the treatment and two more days after finishing it.


Treatment with azithromycin may interact with the use of other medications concomitantly.

As is the case of any of the following medications:

  • Ergotamine derivatives such as ergotamine which is used in the treatment of migraine.
  • Cyclosporine is a drug used in transplant patients.
  • Digoxin is a drug used to treat abnormal heart rhythm.
  • Antacids, these medications are used in digestive-type conditions. If antacids and azithromycin are administered together, the simultaneous administration of both drugs is recommended.
  • Dicumarinic anticoagulants, such as warfarin, are medicines used to prevent the appearance of blood clots.
  • Nelfinavir and zidovudine are the drugs used to treat infections caused by the HIV immunodeficiency virus.
  • Terfenadine is used for the treatment of allergies.
  • Rifabutin is commonly used to treat pulmonary tuberculosis and non-pulmonary diseases caused by mycobacteria.
  • Amiodarone and propafenone are recommended to treat heart rhythm disorders.