Azithromycin is a macrolide antibiotic that works by blocking bacterial protein synthesis. Marketed in New Zealand as Azeetop, it’s prized for its long half‑life and once‑daily dosing, making it a go‑to for respiratory and skin infections.
The drug binds to the 50S ribosomal subunit, preventing the elongation of peptide chains. This action is bacteriostatic at low concentrations and becomes bactericidal as levels rise. Because it concentrates in tissues-especially lung and sinus mucosa-therapeutic levels persist for days after the last dose.
Guidelines in New Zealand often list it as a first‑line option for atypical pneumonia caused by Mycoplasma or Legionella.
| Attribute | Value |
|---|---|
| Drug class | Macrolide |
| Typical adult dose | 500mg on day1, then 250mg daily for 4days |
| Half‑life | ~68hours (tissue) |
| Spectrum | Gram‑positive, some Gram‑negative, atypicals |
| Common side effects | GI upset, mild QT prolongation |
| Resistance concerns | Increasing macrolide‑resistance in S. pneumoniae |
When azithromycin isn’t suitable-due to allergy, resistance, or drug‑interaction risk-clinicians turn to other agents. Below are the most frequently used alternatives.
Amoxicillin is a beta‑lactam penicillin that inhibits cell‑wall synthesis. It’s the backbone of many community‑acquired infection regimens because of its low cost and narrow spectrum.
Doxycycline is a tetracycline antibiotic that blocks protein synthesis at the 30S ribosomal subunit. Its oral bioavailability and anti‑inflammatory properties make it popular for acne, Lyme disease, and certain rickettsial infections.
Clarithromycin is a second‑generation macrolide. It shares a similar mechanism with azithromycin but has a shorter half‑life and stronger CYP3A4 inhibition, leading to more drug interactions.
Levofloxacin is a fluoroquinolone that targets bacterial DNA gyrase and topoisomerase IV. It offers excellent Gram‑negative coverage and penetrates respiratory tissue well.
Moxifloxacin is another fluoroquinolone with enhanced activity against anaerobes and atypicals, often reserved for severe pneumonia.
Ceftriaxone is a third‑generation cephalosporin administered intravenously. It provides broad Gram‑negative coverage and is the preferred inpatient choice for meningitis and gonorrhea.
| Drug | Class | Typical Adult Dose | Half‑Life | Spectrum | Key Side Effects |
|---|---|---|---|---|---|
| Azithromycin (Azeetop) | Macrolide | 500mg Day1, then 250mg×4days | ≈68h (tissue) | Gram+, atypicals, limited Gram‑‑ | GI upset, QT prolongation |
| Amoxicillin | Penicillin | 500mg×3daily | 1-1.5h | Gram+, some Gram‑‑ | Rash, GI upset |
| Doxycycline | Tetracycline | 100mg×2daily | ≈18h | Broad (incl. atypicals) | Photosensitivity, esophagitis |
| Clarithromycin | Macrolide | 500mg×2daily | ≈5h | Similar to azithro | CYP3A4 interactions, GI |
| Levofloxacin | Fluoroquinolone | 500mg×1daily | ≈7h | Broad Gram‑‑ + atypicals | Tendonitis, QT prolongation |
| Moxifloxacin | Fluoroquinolone | 400mg×1daily | ≈12h | Broad + anaerobes | GI, CNS effects |
| Ceftriaxone | Cephalosporin | 1‑2g IV/IM×1daily | ≈8h | Broad Gram‑‑, some Gram+ | Injection site pain, biliary sludging |
Putting these factors together creates a simple mental flowchart: start with the infection type, then check local resistance, then weigh cardiac risk, and finally consider cost and dosing convenience.
Azithromycin’s long half‑life reduces the need for strict adherence, but it can still prolong the QT interval. Co‑prescribing with other QT‑prolonging agents (e.g., quinine, certain antipsychotics) raises the risk of torsades. Clarithromycin has a far stronger CYP3A4 inhibition, leading to higher interaction potential with statins and oral contraceptives.
Fluoroquinolones carry warnings about tendon rupture, especially in patients over 60 or those on steroids. Doxycycline should be taken with plenty of water to prevent esophageal irritation.
Choosing the right drug isn’t just about individual cure-it’s part of a broader effort to preserve antibiotic effectiveness. Antibiotic stewardship programs in NZ hospitals use local antibiograms to guide empiric therapy. Understanding the mechanism of action (e.g., macrolide vs fluoroquinolone) helps clinicians predict cross‑resistance and avoid unnecessary broad‑spectrum use.
Other related topics worth exploring include:
Current evidence shows azithromycin does not improve outcomes in uncomplicated COVID‑19. It may be used only if a bacterial co‑infection is confirmed.
If you’re on drugs that already prolong the QT interval (e.g., sotalol, quinidine), discuss alternatives with your doctor. Azithromycin can add a modest QT effect, which may be risky for some patients.
The metallic or bitter sensation is a common gastrointestinal side effect of macrolides. Taking the pill with food can lessen the taste, though food may slightly delay absorption.
Azithromycin is classified as pregnancy category B (US) and is generally considered safe. Nevertheless, a clinician should weigh the benefit against any potential risk.
Doxycycline has strong anti‑inflammatory properties and is taken twice daily for 6‑12weeks, while azithromycin is used as a short‑course (often a 3‑day “pulse”). Doxycycline is usually preferred for moderate to severe acne.
Levofloxacin is favoured when a pathogen is known to be resistant to macrolides, or when the infection involves Gram‑negative organisms such as Haemophilus influenzae. It’s also an option for patients with macrolide allergy.
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