Reviewed on 3/14/2022

What Is Azithromycin and How Does It Work?

Azithromycin is used to treat certain bacterial infections (including sinusitis, pneumonia). It is a macrolide-type antibiotic. It works by stopping the growth of bacteria.

  • This medication will not work for viral infections (such as common cold, flu). Unnecessary use or misuse of any antibiotic can lead to its decreased effectiveness.
  • Azithromycin is available under the following different brand names: Zithromax, and Zmax.

Susceptible organisms

  • Actinobacillus actinomycetemcomitans, Actinomyces israelii, Actinomyces naeslundii, Actinomyces odontolyticus, Afipia felis, Arachnia propionica, Arcanobacterium (Corynebacterium) haemolyticum, Bartonella henselae, Bartonella quintana, Bordetella pertussis, Borrelia burgdorferi, Borrelia recurrentis, Klebsiella granulomatis, Campylobacter jejuni, Chlamydia pneumoniae (TWAR agent), Chlamydia trachomatis, Haemophilus ducreyi, Haemophilus influenzae, Legionella spp, Mycobacterium simiae, Mycobacterium scrofulaceum, Mycobacterium xenopi, Mycoplasma pneumoniae, Moraxella (Branhamella) catarrhalis, Neisseria gonorrhoeae, Staphylococcus aureus, Streptococcus (group C and G), Streptococcus agalactiae (group B), Streptococcus bovis (group D), Streptococcus intermedius group (Streptococcus anginosus, Streptococcus intermedius, Streptococcus constellatus), Streptococcus pneumoniae, Streptococcus pyogenes (group A), viridans streptococci
  • First-line therapy: A felis, B henselae, B quintana, B pertussis, C jejuni, C pneumoniae (TWAR agent), C trachomatis, H ducreyi, H influenzae, Legionella spp, M scrofulaceum, M simiae, M xenopi, N gonorrhoeae


Fungal Skin Infections: Types, Symptoms, and Treatments See Slideshow

What Are Dosages of Azithromycin?

Dosages of Azithromycin

Adult and Pediatric Dosage Forms & Strengths

Powder for solution

  • 500 mg
  • 25 g

Suspension reconstituted

  • 100 mg / 5mL
  • 200 mg / 5mL


  • 1 mg


  • 250 mg
  • 500 mg
  • 600 mg

Oral suspension, Pediatric

  • 100 mg / 5mL
  • 200 mg / 5mL

Dosage Considerations – Should be Given as Follows:

Acute Bacterial Exacerbations of Chronic Obstructive Pulmonary Disease

  • 500 mg orally once, then 250 mg once daily for 4 days
  • Alternatively, 500 mg orally once/day for 3 days

Acute Otitis Media

  • 500 mg orally once, then 250 mg once daily for 4 days
  • Younger than 6 months: Safety and efficacy not established
  • 6 months and older: 30 mg/kg of oral suspension once or 10 mg/kg orally once daily for 3 days or 10 mg/kg once on day 1 followed by 5 mg/kg on days 2-5

Genital Ulcer Disease (Chancroid)

  • 1 g orally once

Acute Bacterial Sinusitis

  • 500 mg/day orally for 3 days or 2 g orally once

Pediatric: Zmax: 2g orally once

  • 10 mg/kg of oral suspension orally once daily for 3 days

Community-Acquired Pneumonia

  • 500 mg orally once, then 250 mg once daily for 4 days
  • 2 g extended-release suspension orally once
  • 500 mg intravenously (IV) as a single dose for at least 2 days; follow with oral therapy with a single dose of 500 mg to complete 7-10 days course of therapy

Younger than 6 months: Safety and efficacy not established

  • 6 months and older: 10 mg/kg orally on day 1, followed by 5 mg/kg orally on days 2 through 5
  • 6 months and older (Zmax): 60 mg/kg orally once; not to exceed 2 g
  • Pharyngitis/Tonsillitis500 mg orally once, then 250 mg once daily for 4 days
  • Alternatively, 12 mg/kg orally; not to exceed 500 mg on day 1 followed by 6 mg/kg; not to exceed 250 mg on days 2 through 5

Younger than 2 years: Safety and efficacy not established

  • 2 years and older: 12 mg/kg orally once daily for 5 days; not to exceed 500 mg/day
  • Uncomplicated Skin/Skin Structure Infections
  • 500 mg orally once, then 250 mg once daily for 4 days

Cat Scratch Disease

  • Greater than 45.5 kg: 500 mg orally once, then 250 mg once daily for 4 days
  • Pediatric, off-label: Less than 45.5 kg: 10 mg/kg orally as a single dose; then 5 mg/kg orally once/day on days 2 through 5
  • Less than 45.5 kg: 500 mg orally once, then 250 mg once daily for 4 days

Pertussis (Off-label)

  • 500 mg orally once, then 250 mg once daily for 4 days

Acute Pelvic Inflammatory Disease

  • 500 mg intravenously (IV) over 1 hour once daily for 1-2 days; follow therapy by oral route with 250 mg once/day for 5 days to complete a 7-day therapy

Uncomplicated Gonococcal Infections

CDC STD guidelines: MMWR Recomm Rep. June 5, 2015:64(RR3);1-137

Sexual assault

Prophylaxis of sexually transmitted diseases (STDs) such as gonorrhea after sexual assault per CDC guidelines includes the following 3-drug regimen:

  • Ceftriaxone 250 mg intramuscularly (IM) once PLUS
  • Azithromycin 1 g orally once PLUS
  • Metronidazole or tinidazole 2 g orally once

If alcohol has been recently ingested or emergency contraception is provided, metronidazole or tinidazole can be taken by the victim at home rather than as directly observed therapy to avoid drug interactions

Mycobacterium Avium Complex Infection


  • Primary prophylaxis: 1.2 g orally once weekly or 600 mg orally twice weekly; with or without rifabutin 300 mg once daily
  • Secondary prophylaxis: 500-600 mg orally once/day in combination with ethambutol

Younger than 6 years: Safety and efficacy not established

  • 6 years and older primary prophylaxis: 20 mg/kg orally once weekly; not to exceed 1200 mg or 5mg/kg/day once/day; not to exceed 250 mg/day
  • 6 years and older secondary prophylaxis: 5 mg/kg/day orally once/day; not to exceed 250 mg/day in combination with ethambutol with or without rifabutin


  • 250 mg orally once daily in combination with ethambutol 15 mg/kg/day with or without rifabutin 300 mg/day
  • Alternative regimen: 500 mg orally 3 times weekly in combination with ethambutol 15 mg/kg/day with or without rifabutin 300 mg/day
  • Pediatric: 10-12 mg/kg/day orally; not to exceed 500 mg; used in combination with ethambutol; if severe disease patient should also receive rifabutin

Endocarditis (Off-label)


  • 500 mg orally 30-60 min before procedure

Current American Heart Association (AHA) guidelines recommend only for high-risk patients

  • Chlamydia Trachomatis Infection (Pediatric, Off-label)
  • Greater than 45 mg/kg: 1 g orally as a single dose

Dosage Considerations

Not for use in patients with pneumonia judged to be inappropriate for oral therapy because of moderate to severe illness or risk factors not containing all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Are Side Effects Associated with Using Azithromycin?

Side effects of azithromycin include:

Additional side effects of azithromycin from postmarketing reports include:

This is not a complete list of side effects and other serious side effects or health problems may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.


Bowel regularity means a bowel movement every day. See Answer

What Other Drugs Interaction with Azithromycin?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

  • Severe Interactions of azithromycin include:
    • pimozide
  • Azithromycin has serious interactions with at least 38 different drugs.
  • Azithromycin has moderate interactions with at least 144 different drugs.
  • Azithromycin has mild interactions with at least 38 different drugs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Azithromycin?


  • This medication contains azithromycin. Do not take Zithromax or Zmax if you are allergic to azithromycin or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


  • Hypersensitivity
  • History of cholestatic jaundice or hepatic impairment associated with prior azithromycin use
  • Coadministration with pimozide

Effects of Drug Abuse

  • None

Short-term Effects

  • See "What Are Side Effects Associated with Using Azithromycin?"

Long-term Effects

  • See “What Are Side Effects Associated with Using Azithromycin?”


  • Use with caution in abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepatic failure have been reported, some of which have resulted in death; discontinue azithromycin immediately if signs and symptoms of hepatitis occur.
  • Injection-site reactions can occur with the IV route.
  • In the treatment of gonorrhea or syphilis, perform susceptibility culture tests before initiating azithromycin therapy; may mask or delay symptoms of incubating gonorrhea or syphilis.
  • Bacterial or fungal superinfection may result from prolonged use.
  • Prolonged QT interval: Cases of torsades de pointes have been reported during postmarketing surveillance; use with caution in patients with known QT prolongation, history of torsades de pointes, congenital long QT syndrome, bradyarrhythmias, or uncompensated heart failure; also use with caution if co-administering with drugs that prolong QT interval or proarrhythmic conditions (e.g., hypokalemia, hypomagnesemia); elderly patients may be more susceptible to drug-associated effects on QT interval.
  • Pneumonia: oral azithromycin is safe and effective only for community-acquired pneumonia (CAP) due to C pneumoniae, H influenzae, M pneumoniae, or S pneumonia.
  • Cases of Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) reported; despite successful symptomatic treatment of allergic symptoms, when symptomatic therapy was discontinued, allergic symptoms recurred soon thereafter in some patients without further azithromycin exposure; if allergic reaction occurs, the drug should be discontinued and appropriate therapy instituted; physicians should be aware that allergic symptoms may reappear when symptomatic therapy discontinued.
  • Endocarditis prophylaxis: Indicated only for high-risk patients, per current AHA guidelines.
  • Use caution in renal impairment (CrCl less than 10 mL/min).
  • Use caution in patients with myasthenia gravis (exacerbation may occur).
  • Immediate release and extended-release suspensions are not interchangeable.
  • Use extended-release suspension only for the treatment of infections that are proven or strongly suspected to be caused by susceptible bacteria.
  • Clostridium difficile associated diarrhea (CDAD) is reported and may range in severity from mild diarrhea to fatal colitis; treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of Clostridium difficile.
  • Serious allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions including Stevens-Johnson Syndrome, and toxic epidermal reported; if allergic reaction occurs, the drug should be discontinued and appropriate therapy instituted; physicians should be aware that allergic symptoms may reappear after symptomatic therapy has been discontinued.
  • The following use in neonates (treatment up to 42 days of life), infantile hypertrophic pyloric stenosis was reported; direct parents and caregivers to contact physician if vomiting or irritability with feeding occurs.
  • Prescribing antibiotics in absence of a proven or strongly suspected bacterial infection is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

Pregnancy and Lactation

  • Azithromycin use may be acceptable during pregnancy. Either animal studies show no risk but human studies are not available or animal studies showed minor risks and human studies were done and showed no risk.
  • It is unknown whether azithromycin is excreted into breast milk; use with caution while breastfeeding.
Medscape. Azithromycin.

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