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Azithromycin: Mechanism of Action, Side Effects and Dosage

Macrolide antibiotics are based on a complex lactone ring structure. The reference substance erythromycin is prescribed less frequently in favor of better-tolerated successors such as clarithromycin, roxithromycin, and azithromycin. Azithromycin is the standard preparation in urology.

Mechanism of Action:

Bacteriostatic by inhibiting bacterial protein biosynthesis. Azithromycin binds to the 50S subunit of the ribosome, where it prevents translation and peptidyl transferase activity.

Antibiotic Spectrum of Azithromycin:

Pneumococci, streptococci, mycoplasmas, Ureaplasma urealyticum, Legionella, Chlamydia, Actinomyces israeli. Treponema pallidum and Peptostreptococcus are less sensitive to azithromycin. There is variable sensitivity and partial resistance in staphylococci, enterococci, Mycoplasma genitalium, and Neisseria gonorrhoeae.

Urological Indications for Azithromycin:

Sexually-transmitted Non-gonococcal urethritis, epididymitis, or prostatitis.

Pharmacokinetics of Azithromycin:

40% bioavailability, high distribution volume, and good tissue penetration.
The half-life is 10–12 hours in the blood and over 60 hours in tissue. Mainly excreted via the bile.

Side Effects of Azithromycin

GI tract: Nausea, vomiting, diarrhea, pseudomembranous enterocolitis. Rarely, liver dysfunction with cholestasis and pancreatitis is possible.
Other: Rarely, skin rash, photosensitivity, dizziness, reversible hearing impairment, QT prolongation with risk of malignant cardiac arrhythmias.

Drug Interactions:

Caution (possible potentiation) with theophylline, carbamazepine, Marcumar, digoxin, and midazolam. No simultaneous therapy with ergotamine-containing medications.

Contraindications:

Allergy to macrolides. QT prolongation. Severe liver disease. Caution in severe renal insufficiency (GFR below 10 ml/min).

Dosage of Azithromycin

The standard dose for azithromycin is 1500 mg, administered in 500 mg p.o. once daily for three days. Alternatively, prescribe 500 mg on day 1 and 250 mg on days 2 5.
Children receive 10 mg/kg body weight 1-0-0 for 3 days or 10 mg/kg body weight on day 1 and 5 mg/kg body weight on days 2 5.
Treatment of uncomplicated chlamydia infection: 1000 mg once p.o. However, low-dose single therapy is ineffective against Mycoplasma genitalium and is believed to be responsible for increasing macrolide resistance. A single dose is an option if infection with M. genitalium is ruled out.
Treatment of infection with Mycoplasma genitalium: 500 mg on day 1 and 250 mg on days 2 5. The current German guideline for urethritis recommends a higher off-label dosage of azithromycin over four days: 1000 mg p.o. on the first day and 500 mg p.o. for the next three days.

Ciprofloxacin

Index

Fosfomycin

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

References

Simon und Stille 1997 SIMON, C. ; STILLE, W.: Antibiotika-Therapie in Klinik und Praxis.
9. Auflage.
Stuttgart New York : Schattauer, 1997

DDG, DSTIG, DGU, and RKI, “S3-Leitlinie: Management der Urethritis bei männlichen Jugendlichen und Erwachsenen.” [Online]. Available: https://register.awmf.org/assets/guidelines/013-099l_S3_Management-Urethritis-maennliche-Jugendliche-Erwachsene_2025-02.pdf

Deutsche Version: Pharmakologie und Nebenwirkungen von Azithromycin

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