Azithromycin: Uses, Dosage, Side Effects, and Precautions

What is azithromycin?

Azithromycin (azithromycin dihydrate) is an antibiotic from the macrolide class, commonly used to treat respiratory infections, sexually transmitted diseases, bacterial diarrhea, and other infectious diseases.

It is derived from erythromycin, an older macrolide that is now rarely used in medical practice, except in certain ointments and eye drops. Today, azithromycin and clarithromycin are the most widely used antibiotics in this class.

Azithromycin has gained popularity due to its convenient dosing regimen—typically just one tablet per day for 3 to 5 days. Some infections can even be treated with a single dose of this antibiotic.

In this article, we will cover the main uses, interactions, contraindications, and side effects of azithromycin. This text is designed to be more practical and accessible than a standard drug leaflet, offering useful information for patients.

The following content is based on various leaflets published by pharmaceutical manufacturers.

What azithromycin is used for?

Azithromycin is prescribed to treat a variety of bacterial infections, including:

• Pneumonia.
• Urethritis caused by gonorrhea.
• Chlamydial urethritis.
• Tonsillitis.
• Sinusitis.
• Whooping cough (Pertussis).
• Bacterial diarrhea.
• Soft chancre.
• Acne.
• Cholera.
• Otitis (ear infections).
• Pelvic inflammatory disease (PID).
• Syphilis.

Azithromycin is effective against various bacteria, including:

Gram-positive bacteria:

• Staphylococcus aureus.
• Streptococcus agalactiae.
• Streptococcus pneumoniae.
• Streptococcus pyogenes.
• Streptococcus viridans.

Gram-negative bacteria:

• Bordetella pertussis.
• Campylobacter jejuni.
• Haemophilus ducreyi.
• Haemophilus influenzae.
• Haemophilus parainfluenzae.
• Legionella pneumophila.
• Moraxella catarrhalis.
• Neisseria gonorrhoeae.

Anaerobes:

• Clostridium perfringens.
• Peptostreptococcus spp.
• Prevotella bivia.

Other species:

• Borrelia burgdorferi.
• Chlamydia trachomatis.
• Chlamydophila pneumoniae.
• Mycoplasma pneumoniae.
• Treponema pallidum
• Ureaplasma urealyticum.

Is Azithromycin Effective for Urinary Tract Infections (UTIs)?

Azithromycin is not a recommended treatment for common urinary tract infections (UTIs). One reason is that it does not reach high concentrations in the urine, making it less effective against bacteria in the urinary tract. Additionally, it has limited activity against Escherichia coli, which causes over 80% of UTIs.

However, azithromycin is used for urethritis caused by Chlamydia trachomatis and, in some cases, Neisseria gonorrhoeae.

The best treatment options for simple urinary infection are discussed in the article: Treatment of Urinary Tract Infection (UTI) With Antibiotics.

Brand Names

Azithromycin is available in generic form or under various brand names. Some of the most common brands in English-speaking countries include:

• Zithromax.
• Zmax.
• Azasite (eye drops).
• Azyth.
• Z-Pak.
• Tri-Pak.

Presentations

Azithromycin is available in different forms and dosages, including:

• Tablets: 250 mg, 500 mg, and 600 mg.
• Oral suspension: 200 mg/5 mL.
• Extended-release suspension: 2 g single-dose bottle.
• Injection: 500 mg vial for intravenous use.
• Ophthalmic solution: 1% for bacterial eye infections.

Dosage and Administration

Tablets

Azithromycin tablets can be taken with or without food. It should be taken once a day, preferably at the same time each day. If you forget a dose, take it as soon as possible. If it is close to the next scheduled dose, skip the missed dose—do not double up.

Store the medication in a dry, cool place away from heat and moisture.

Recommended Dosage for Adults:

• Sinusitis: 500 mg once daily for 3 days.
• Chlamydia: 1000 mg as a single dose.
• Pneumonia: 500 mg on the first day, followed by 250 mg daily for 4 days.
• Soft chancre: 1000 mg as a single dose.
• Pharyngitis (Tonsillitis): 500 mg on the first day, followed by 250 mg daily for 4 days.

Azithromycin has a long half-life, remaining active for about 70 hours per gram taken. This allows for shorter treatment durations compared to many other antibiotics, which often require 10-14 days of multiple daily doses.

Oral Suspension

Azithromycin dihydrate oral suspension comes in powder form for reconstitution. Shake the bottle well before opening it to loosen any powder stuck to the bottom. Then, add filtered water (or any type of drinking water) up to the mark indicated on the bottle. Close the bottle and shake again to ensure all the powder is fully dissolved. Once reconstituted, the solution is ready for use, and no additional water should be added.

Both the 600 mg and 900 mg bottles will, after dilution, form a solution containing 40 mg of azithromycin per milliliter. This means that each 5 ml syringe included with the bottle contains 200 mg of azithromycin.

If the required dose is 500 mg, you should take two full 5 ml syringes plus one half-filled syringe (2.5 ml).

Recommended Dosage for Children

The dosage of azithromycin for children is based on body weight, calculated as 30 mg per kg (13.6 mg per lb) of the child’s weight. For example, a child weighing 20 kg (44 lbs) will require a total dose of 600 mg of azithromycin.

There are different administration schedules for this total dose:

• 3-day regimen: The child takes 10 mg/kg (4.5 mg/lb) once daily for 3 consecutive days.
• 5-day regimen: The child takes 10 mg/kg (4.5 mg/lb) on the first day, followed by 5 mg/kg (2.3 mg/lb) once daily from the second to the fifth day.
• Acute otitis media: A single dose of 30 mg/kg (13.6 mg/lb) can be used for treatment.

Streptococcal pharyngitis (Tonsillitis):

• 5-day regimen: 10 mg/kg (4.5 mg/lb) on day 1, followed by 5 mg/kg (2.3 mg/lb) daily for 4 days.
• 3-day regimen: 10 mg/kg (4.5 mg/lb) once daily for 3 days.

Weight-Based Dosage Table (Metric & Imperial Units)

Weight (kg/lbs)	3-Day Regimen	5-Day Regimen	Total Vial Requirement
< 15 kg (33 lbs)	10 mg/kg (4.5 mg/lb) once daily for 3 days.	10 mg/kg (4.5 mg/lb) on day 1, then 5 mg/kg (2.3 mg/lb) for 4 days.	600 mg
15-25 kg (33-55 lbs)	200 mg (5 mL) once daily for 3 days.	200 mg (5 mL) on day 1, then 100 mg (2.5 mL) for 4 days.	600 mg
26-35 kg (57-77 lbs)	300 mg (7.5 mL) once daily for 3 days.	300 mg (7.5 mL) on day 1, then 150 mg (3.75 mL) for 4 days.	900 mg
36-45 kg (79-99 lbs)	400 mg (10 mL) once daily for 3 days.	400 mg (10 mL) on day 1, then 200 mg (5 mL) for 4 days.	1200 mg (2 bottles of 600 mg)
> 45 kg (99+ lbs)	Same as adult dose.	Same as adult dose.	1500 mg (1 bottle of 900 mg + 1 bottle of 600 mg)

Side Effects

Azithromycin is generally considered a safe antibiotic with a low incidence of serious side effects. The most common side effects include nausea, vomiting, stomach cramps, and diarrhea, occurring in approximately 5-10% of patients. These gastrointestinal symptoms are more frequent when taking high doses (≥1 gram per day).

Contraindications

• Liver Disease: Azithromycin should not be used in patients with liver conditions, particularly hepatitis or cirrhosis, as it may have hepatotoxic effects.
• Myasthenia Gravis: Patients with Myasthenia Gravis should avoid azithromycin, as it may exacerbate muscle weakness.
• Pregnancy and Breastfeeding:
  • While there is no confirmed evidence of birth defects, azithromycin is generally not recommended during pregnancy, as its safety has not been definitively established.
  • This antibiotic should also be avoided during breastfeeding, unless prescribed by a healthcare provider.

Further reading: Mixing Antibiotics with Alcohol: What’s the Risk?

Drug Interactions

Azithromycin can interact with various medications, potentially altering their effectiveness or increasing the risk of adverse effects.

• Amiodarone – May increase amiodarone toxicity, leading to potential heart rhythm complications.
• Antacids – May reduce azithromycin’s effectiveness by interfering with its absorption.
• Cyclosporine – May increase cyclosporine toxicity, requiring dose adjustments and monitoring.
• Hydroxychloroquine – May increase the risk of cardiac arrhythmias due to prolonged QT interval.
• Tacrolimus – May increase tacrolimus toxicity, necessitating close monitoring of drug levels.
• Digoxin – May increase digoxin toxicity, requiring careful monitoring of digoxin levels.
• Nelfinavir – May increase azithromycin toxicity, potentially leading to stronger side effects.
• Warfarin – May enhance the anticoagulant effect of warfarin, increasing the risk of bleeding.
• Atorvastatin – May increase the risk of muscle damage (rhabdomyolysis), potentially leading to muscle pain or weakness.

⚠ Note: This list is not exhaustive. Always consult a healthcare provider before taking azithromycin with other medications to avoid harmful interactions.

Does Azithromycin Affect the Contraceptive Pill?

No, azithromycin does not interfere with or reduce the effectiveness of hormonal contraceptives, including pills, patches, injections, or implants. The mini-pill and morning-after pill are also not affected by azithromycin.

Does Azithromycin Help Treat COVID-19?

There is no scientific evidence that azithromycin is effective in treating viral infections, including COVID-19

⚠ Important Warning:

• Combining azithromycin with hydroxychloroquine increases the risk of cardiac arrhythmias, as both drugs prolong the QT interval (the depolarization and repolarization time of the heart’s ventricles).

Azithromycin can be prescribed to COVID-19 patients only if they develop a bacterial respiratory infection (such as bacterial pneumonia) as a complication of the viral infection.

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References

• Azithromycin 200mg/5ml Powder for Oral Suspension – Sandoz Limited.
• Azithromycin – NHS.
• Azithromycin Dihydrate – NIH National Library of Medicine.
• Azithromycin (systemic): Drug information – UpToDate.
• Azithromycin, clarithromycin, and telithromycin – UpToDate.

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