Zithrolide contains azithromycin, a prescription antibiotic, in 250 mg and 500 mg tablets. It is used for chest and sinus infections, throat and skin infections, and some sexually transmitted infections. Its distinctive feature is a very short course — often just three days.
What is Zithrolide?
Zithrolide is Schedule 4 — prescription-only:
| Product | Contains |
|---|---|
| Zithrolide 250 mg | Azithromycin 250 mg tablet |
| Zithrolide 500 mg | Azithromycin 500 mg tablet |
Azithromycin is widely available in South Africa under other names, including Azrotrin, Azithromycin 500 Biotech and Zithromax. Being dispensed one rather than another is ordinary generic substitution.
Azithromycin is a macrolide antibiotic. It binds to the bacterial ribosome — the machinery that assembles proteins — and blocks it, so the bacterium cannot make the proteins it needs to grow and divide. Human ribosomes are structured differently, which makes the effect selective.
What makes azithromycin distinctive is how it behaves in the body, and this explains almost everything unusual about how it is prescribed:
- It concentrates inside cells and in tissue, reaching levels at the site of infection far higher than in the blood. White blood cells effectively carry it to where it is needed.
- It has a very long half-life, lingering in tissue for days after the last dose.
Together these mean a three-day course keeps working for around ten days. A course that looks suspiciously short is not under-treatment — it is a property of the medicine. Finishing a three-day pack is completing the course, and this is a common and understandable source of doubt.
The two strengths reflect different regimens. Some courses use 500 mg once daily for three days; others use 500 mg on day one then 250 mg for four days; and some infections are treated with a single larger dose. Follow the schedule you were given rather than assuming.
Macrolides are the standard alternative for people allergic to penicillin, being chemically unrelated — one of the main reasons azithromycin is prescribed. It also covers “atypical” organisms such as Mycoplasma, Chlamydia and Legionella that penicillins miss entirely.
What is Zithrolide commonly used for?
A doctor may prescribe it for:
- Chest infections, including community-acquired pneumonia and infective exacerbations of COPD.
- Sinusitis, where symptoms are persistent or severe.
- Throat and tonsil infections, particularly in penicillin allergy.
- Middle ear infections.
- Chlamydia, as a single-dose or short-course treatment.
- Some other sexually transmitted infections, often alongside another antibiotic.
- Skin and soft-tissue infections.
- Whooping cough (pertussis), and preventing it in close contacts.
- Some gut infections, including travellers’ diarrhoea caused by susceptible bacteria.
It has no effect on viruses. Colds, flu, most sore throats, most coughs and most bronchitis are viral, and an antibiotic will not shorten them or prevent complications.
How Zithrolide fits into this medicine category
| Group | Examples | Typical role |
|---|---|---|
| Macrolides | Azithromycin (Zithrolide), clarithromycin, erythromycin | Chest infections, atypical organisms, penicillin allergy |
| Penicillins | Amoxicillin, flucloxacillin | Common first-line choices |
| Penicillin + inhibitor | Co-amoxiclav | Where resistance is likely |
| Cephalosporins | Cefalexin | Skin, throat, urinary infections |
| Tetracyclines | Doxycycline | Chest, skin, STIs, tick bite fever |
| Nitroimidazoles | Metronidazole | Anaerobic and some parasitic infections |
See the antibiotics and antimicrobials hub.
What to check before using Zithrolide
Complete the course you were given, however short it looks.
Take it at the same time each day. It can generally be taken with or without food, though food may reduce stomach upset.
Separate it from antacids containing aluminium or magnesium by at least two hours, as they reduce absorption.
Tell your doctor or pharmacist if you:
- Have any heart condition, particularly a rhythm disorder or prolonged QT interval, a slow heart rate, or heart failure. Azithromycin can affect heart rhythm, and this is its most important caution.
- Have low potassium or magnesium.
- Take other medicines affecting heart rhythm — some antipsychotics, antidepressants, antifungals, antimalarials and antiarrhythmics.
- Have liver disease. Azithromycin is cleared mainly by the liver.
- Have kidney disease.
- Have myasthenia gravis, which macrolides can worsen.
- Have had a reaction to any macrolide antibiotic before.
- Take warfarin, digoxin, ciclosporin, colchicine, or ergot medicines for migraine.
- Take statins, where muscle side effects can increase.
- Are pregnant or breastfeeding.
- Are being treated for a sexually transmitted infection, so partners can be tested and treated.
Possible cautions and when to ask a pharmacist or doctor
Common effects are nausea, diarrhoea, abdominal pain, vomiting and headache. Azithromycin is generally better tolerated than older macrolides such as erythromycin.
Stop and seek medical attention urgently if you develop:
- Palpitations, fainting, dizziness or an irregular heartbeat — given the heart rhythm effect.
- Swelling of the face, lips, tongue or throat, difficulty breathing, or a widespread hives-like rash — a serious allergic reaction. Call emergency services.
- A rash, blistering or peeling skin, or sores in the mouth or eyes. Serious skin reactions are rare but recognised.
- Severe, watery or bloody diarrhoea, during or in the weeks after the course — possible C. difficile infection, where anti-diarrhoeal medicines should not be used.
- Yellowing of the eyes or skin, dark urine or pale stools — possible liver problems.
- Muscle weakness, particularly if you have myasthenia gravis.
- Hearing loss, ringing in the ears or dizziness, reported with prolonged or high-dose use and usually reversing on stopping.
Contact your doctor if you are no better after two to three days of treatment, or if symptoms worsen at any point.
If you were treated for a sexually transmitted infection, follow the advice about avoiding sex until treatment is complete, and about partner testing. Reinfection is common when partners are not treated, and untreated chlamydia can cause lasting damage to fertility.
Never use antibiotics left over from a previous illness or prescribed for someone else.
Related medicine guides
- Browse Antibiotics, Antifungals & Antimicrobials guides
- Read: Azrotrin used for
- Read: Metronidazole used for
Frequently asked questions
What is Zithrolide 500 mg used for? Bacterial infections including chest and sinus infections, throat infections, chlamydia and other STIs, and skin infections. Each tablet contains azithromycin 500 mg.
What is Zithrolide 250 mg used for? The lower strength, used in regimens that step down after a larger first dose, or where a smaller dose is appropriate.
Why is the course only three days? Azithromycin concentrates in tissue and lingers for days after the last dose, so a three-day course keeps working for about ten. Finishing the pack is completing the course.
Will it help flu or a cold? No. Those are viral, and antibiotics have no effect on them.
Can I take it if I am allergic to penicillin? Macrolides are chemically unrelated to penicillins and are the usual alternative. Tell your doctor about any antibiotic allergy.
Can I take it with antacids? Separate them by at least two hours, as antacids reduce absorption.
Does it affect the heart? It can affect heart rhythm, which is its most important caution. Tell your doctor about any heart condition or medicines affecting rhythm.
Does my partner need treatment? For a sexually transmitted infection, yes — partners need testing and treatment, or reinfection is likely.