Azithromycin
Azithromycin is a macrolide antibiotic used to treat a variety of bacterial infections including respiratory infections, skin infections, ear infections, and sexually transmitted diseases.
About Azithromycin
Azithromycin is a macrolide antibiotic also sold under brand names including Zithromax and Z-Pak. It is primarily used to is prescribed to treat: • Respiratory tract infections (bronchitis, pneumonia, sinusitis) • Ear infections (otitis media) • Skin and soft tissue infections • Strep throat and tonsillitis • Sexually transmitted infections (chlamydia, gonorrhea) • Mycobacterium avium complex (MAC) in HIV/AIDS patients • Pertussis (whooping cough) • Certain stomach infections (H. Azithromycin is available in oral tablet (250 mg, 500 mg, 600 mg), oral suspension (100 mg/5 ml, 200 mg/5 ml), oral single-dose packet (1 g), iv injection for reconstitution (500 mg vial), and ophthalmic solution (1%) form. Healthcare providers commonly prescribe Azithromycin for conditions including Atrial Fibrillation, Chronic Obstructive Pulmonary Disease (COPD), Hives (Urticaria), and Osteoarthritis.
Azithromycin at a Glance
- Brand names
- Zithromax, Z-Pak
- Drug class
- Macrolide Antibiotic
- Pregnancy category
- FDA Category Category B — Animal reproduction studies have not shown fetal harm, and observational human data have not demonstrated a clear increase in major malformations. Generally considered acceptable during pregnancy when a macrolide is indicated, though clinicians weigh QT-prolongation and limited long-term data when prescribing.
- Available forms
- Oral tablet (250 mg, 500 mg, 600 mg), Oral suspension (100 mg/5 mL, 200 mg/5 mL), Oral single-dose packet (1 g), IV injection for reconstitution (500 mg vial), Ophthalmic solution (1%)
- Therapeutic categories
- Antibiotics, Macrolides, Respiratory, Infectious Disease
- Conditions treated
- 7 related conditions on this site
What Azithromycin Is Used For
is prescribed to treat:
• Respiratory tract infections (bronchitis, pneumonia, sinusitis) • Ear infections (otitis media) • Skin and soft tissue infections • Strep throat and tonsillitis • Sexually transmitted infections (chlamydia, gonorrhea) • Mycobacterium avium complex (MAC) in HIV/AIDS patients • Pertussis (whooping cough) • Certain stomach infections (H. pylori)
It is effective against many types of bacteria.
Dosage Quick Reference
These are general dosage guidelines for Azithromycin. Your doctor will determine the appropriate dose for your specific situation.
| Condition | Starting Dose | Maintenance Dose |
|---|---|---|
| Community-acquired pneumonia (mild) | 500 mg orally on day 1 | 250 mg once daily on days 2–5 (Z-Pak) |
| Acute bacterial sinusitis or AECB | 500 mg once daily | 500 mg once daily for 3 days |
| Uncomplicated chlamydia | 1 g orally as a single dose | Not applicable — single dose |
| Strep pharyngitis (penicillin-allergic) | 12 mg/kg (max 500 mg) on day 1 | 6 mg/kg once daily on days 2–5 |
| MAC prophylaxis (advanced HIV) | 1.2 g orally once weekly | 1.2 g once weekly while CD4 < 50 |
Side Effects
Common side effects may include:
• Nausea, vomiting, or diarrhea • Stomach pain or upset • Headache • Dizziness • Abnormal taste
Serious side effects (seek immediate medical attention):
• Severe allergic reactions (rash, hives, swelling, difficulty breathing) • Irregular heartbeat or palpitations • Severe diarrhea (may indicate C. difficile infection) • Liver problems (yellowing of skin/eyes, dark urine, severe fatigue) • Hearing problems or ringing in ears • Severe stomach cramps • Muscle weakness or vision changes (signs of myasthenia gravis worsening)
See also: Drug Interactions ↓
Drug Interactions
Azithromycin has fewer cytochrome P450 interactions than other macrolides, but it carries a clinically important QT-prolongation signal and several pharmacodynamic interactions to know.
- QT-prolonging drugs (e.g., amiodarone, sotalol, citalopram, ondansetron, quetiapine, methadone): Additive risk of torsades de pointes and sudden cardiac death. Avoid combinations in patients with congenital long QT, bradycardia, hypokalemia, or hypomagnesemia.
- Warfarin: Case reports describe elevated INR and bleeding when azithromycin is added. Check INR within several days of starting and discontinuing therapy.
- Aluminum- or magnesium-containing antacids: Reduce peak azithromycin absorption when taken simultaneously. Separate dosing by at least 2 hours.
- Digoxin and colchicine (P-glycoprotein substrates): Azithromycin can raise levels of these P-gp substrates, increasing risk of digoxin toxicity or colchicine toxicity (especially in renal impairment). Monitor levels and clinical effects.
- Nelfinavir: Substantially increases azithromycin exposure. Monitor for liver enzyme abnormalities and ototoxicity.
See also: Questions to Ask Your Doctor ↓
Key Considerations
Known drug interactions
Azithromycin has documented interactions with other medications, supplements, and certain foods. Review the Drug Interactions section below and tell your healthcare provider about every medication you take, including over-the-counter products. Jump to section →
Multiple forms available
Azithromycin comes in more than one form (Oral tablet (250 mg, 500 mg, 600 mg), Oral suspension (100 mg/5 mL, 200 mg/5 mL), Oral single-dose packet (1 g), IV injection for reconstitution (500 mg vial), Ophthalmic solution (1%)). The right form for you depends on your condition, ease of use, and your provider's recommendation.
Additional Information
What is ?
Azithromycin is a broad-spectrum macrolide antibiotic widely known by its brand name Zithromax or as the "Z-Pak." It is one of the most commonly prescribed antibiotics worldwide due to its effectiveness against many common bacterial infections and convenient dosing schedule.
How Does Azithromycin Work?
Azithromycin works by interfering with bacterial protein synthesis:
- Binds to the 50S ribosomal subunit of bacteria
- Inhibits bacterial protein production
- Prevents bacterial growth and reproduction (bacteriostatic)
- Can be bactericidal at higher concentrations
- Concentrates in tissues, providing extended antimicrobial activity
- Long half-life allows for once-daily dosing and shorter treatment courses
Spectrum of Activity
Azithromycin is effective against:
- Respiratory pathogens: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumoniae, Legionella
- Atypical bacteria: Chlamydia pneumoniae, Mycoplasma
- Sexually transmitted infections: Chlamydia trachomatis, Neisseria gonorrhoeae (increasingly resistant)
- Skin pathogens: Staphylococcus aureus (not MRSA), Streptococcus pyogenes
- Other: Mycobacterium avium complex, Bordetella pertussis
Common Uses
Respiratory Infections
Community-Acquired Pneumonia:
- Outpatient treatment for mild-moderate CAP
- Often combined with other antibiotics for hospitalized patients
Acute Bacterial Sinusitis:
- Alternative for penicillin-allergic patients
- Usually 3-5 day course
Acute Bacterial Exacerbation of COPD:
- Helps reduce symptoms and duration
Bronchitis:
- Often prescribed though most bronchitis is viral (antibiotics not helpful)
Sexually Transmitted Infections
Chlamydia:
- Single 1-gram dose is first-line treatment
- Highly effective (>95%)
Gonorrhea:
- Must be combined with ceftriaxone due to resistance
- No longer used alone for gonorrhea
Other Infections
Otitis Media (Ear Infection):
- Alternative for penicillin allergy
Strep Throat:
- Alternative for penicillin-allergic patients
- 5-day course
Skin Infections:
- Cellulitis, impetigo (uncomplicated)
MAC Prophylaxis and Treatment:
- Weekly dosing for prevention in advanced HIV/AIDS
- Part of combination therapy for active MAC
Dosage and Administration
Azithromycin dosing varies by indication:
Standard "Z-Pak" for Respiratory Infections:
- Day 1: 500 mg (two 250 mg tablets)
- Days 2-5: 250 mg once daily
- Total course: 1.5 grams over 5 days
Single Dose for Chlamydia:
- 1 gram (1000 mg) as single oral dose
Pediatric Dosing:
- Weight-based: 10-12 mg/kg once daily for 5 days
- Liquid suspension available
MAC Prophylaxis:
- 1200 mg once weekly
Administration Tips:
- Can be taken with or without food
- Take at same time each day
- Complete full course even if feeling better
- Tablets, oral suspension, and IV formulations available
- Oral suspension should be taken on empty stomach (1 hour before or 2 hours after meals)
Important Safety Information
Who Should Not Take Azithromycin?
Do not take azithromycin if you:
- Are allergic to azithromycin, erythromycin, or other macrolide antibiotics
- Are allergic to ketolide antibiotics
- Have a history of cholestatic jaundice/hepatic dysfunction with prior azithromycin use
Use with caution if you have:
- Heart rhythm problems (QT prolongation)
- Liver disease
- Kidney disease (severe)
- Myasthenia gravis
- Low potassium or magnesium levels
Drug Interactions
Medications That Increase Risk of Irregular Heart Rhythm:
- Antiarrhythmics (amiodarone, sotalol)
- Antipsychotics (haloperidol, ziprasidone)
- Antidepressants (citalopram, escitalopram)
- Methadone
- Other QT-prolonging drugs
Other Important Interactions:
- Warfarin - increased bleeding risk
- Digoxin - may increase digoxin levels
- Ergotamine - risk of ergot toxicity
- Cyclosporine, tacrolimus - may increase immunosuppressant levels
- Nelfinavir - increased azithromycin levels
- Antacids (aluminum/magnesium) - separate by 2 hours
Cardiac Safety
⚠️ Important: Azithromycin can cause QT interval prolongation, potentially leading to a rare but serious irregular heartbeat (torsades de pointes). This risk is higher in:
- Patients with existing heart rhythm problems
- Those taking other QT-prolonging medications
- Patients with low potassium or magnesium
- Elderly patients
- Those with heart disease
Inform your doctor of any heart conditions or medications.
Antibiotic Resistance
Responsible use of azithromycin:
- Only take for bacterial infections (not effective for viral infections like cold or flu)
- Complete full course even if feeling better
- Don't save antibiotics for later use
- Don't share with others
- Overuse contributes to antibiotic resistance
Monitoring
Generally minimal monitoring required:
- Most patients don't need blood tests
- If severe diarrhea develops, may test for C. difficile
- For long-term use (MAC treatment): periodic monitoring of liver function
- Monitor for signs of allergic reaction
Managing Side Effects
Gastrointestinal Upset
- Very common, especially nausea and diarrhea
- Taking with food may help (though not required)
- Usually mild and self-limited
- Stay hydrated
Diarrhea
- Most cases mild and resolve after finishing medication
- Severe or persistent diarrhea may indicate C. difficile infection (requires medical attention)
- Probiotics may help but should be separated from antibiotic by 2+ hours
Special Populations
Pregnancy:
- Category B - generally considered safe
- Used when benefits outweigh risks
- Commonly prescribed for pregnancy complications like Group B Strep colonization, chlamydia
Breastfeeding:
- Small amounts pass into breast milk
- Generally considered compatible with breastfeeding
- Monitor infant for diarrhea or thrush
Elderly:
- May be more sensitive to QT prolongation
- Dosage adjustment usually not needed
- Increased risk of C. difficile infection
Kidney Disease:
- Dosage adjustment usually not needed for mild-moderate disease
- Use caution in severe kidney disease
Liver Disease:
- Use with caution
- Contraindicated if previous liver problems with azithromycin
Advantages of Azithromycin
Convenient Dosing:
- Once-daily dosing
- Short treatment courses (often 3-5 days)
- Single-dose treatment for chlamydia
- Long tissue half-life provides extended coverage
Tolerability:
- Generally well-tolerated
- Fewer drug interactions than erythromycin
- Less GI upset than erythromycin
Efficacy:
- Broad spectrum of activity
- Effective against atypical pathogens
- High tissue concentrations
When to Contact Your Doctor
Seek immediate medical attention if you experience:
- Signs of severe allergic reaction (difficulty breathing, severe rash, swelling of face/throat)
- Irregular heartbeat, palpitations, or chest pain
- Fainting or severe dizziness
- Severe diarrhea (especially with blood or mucus)
- Severe stomach cramps
- Yellowing of skin or eyes
- Dark urine
- Unusual tiredness or weakness
- Hearing problems or ringing in ears
Contact your doctor for non-emergency issues:
- Mild to moderate diarrhea lasting more than 2 days after finishing medication
- Persistent nausea or vomiting
- New rash or itching
- Symptoms not improving after 2-3 days of treatment
- Questions about whether you need to complete the full course
Effectiveness
When used appropriately, azithromycin is highly effective:
- Chlamydia: >95% cure rate with single dose
- Community-Acquired Pneumonia: 85-95% clinical success
- Sinusitis: Comparable to other first-line antibiotics
- Strep Throat: 85-90% cure rate
Storage
- Tablets: Store at room temperature (68-77°F) in original container, protected from light and moisture
- Oral Suspension: After reconstitution, stable for 10 days at room temperature or refrigerated (do not freeze)
- Keep out of reach of children
Cost and Availability
Azithromycin is available as an affordable generic medication. The "Z-Pak" (6-tablet pack) is widely available and covered by most insurance plans. Single-dose packets for chlamydia treatment are also commonly stocked at pharmacies.
Important Reminders
- Azithromycin only treats bacterial infections
- Will not work for viral infections (colds, flu, most sore throats)
- Unnecessary use contributes to antibiotic resistance
- Complete the full prescribed course
- Don't save leftover antibiotics
- Don't share antibiotics with others
Disclaimer: This information is for educational purposes only and is not intended to replace professional medical advice, diagnosis, or treatment. Always consult your physician or other qualified healthcare provider with any questions about a medical condition or medication.
Frequently Asked Questions
Questions to Ask Your Doctor About Azithromycin
Consider discussing these topics at your next appointment:
- Is azithromycin actually the best antibiotic for my type of infection, or are there alternatives with less heart risk?
- Do any of my current medications increase my QT interval or interact with azithromycin?
- How will we know if the antibiotic is working, and when should I follow up if I am not improving?
- Should I have an ECG before starting if I have heart disease or take other rhythm-affecting drugs?
Medical Disclaimer: This information is for educational purposes only and should not be considered medical advice. Always consult with your healthcare provider before starting, stopping, or changing any medication. Your doctor can provide personalized recommendations based on your specific health condition and medical history.