Most people think food poisoning is just a bad day with stomach cramps and diarrhea. But when it’s caused by Campylobacter, it can turn serious-especially in kids, older adults, or anyone with a weak immune system. If your symptoms last more than a few days, or you’re running a high fever, vomiting blood, or showing signs of dehydration, you might need more than rest and fluids. That’s where clarithromycin comes in.
Campylobacter jejuni is the most common cause of bacterial gastroenteritis in the U.S., Europe, and New Zealand. It’s not some rare bug-it’s in undercooked chicken, unpasteurized milk, and contaminated water. In Wellington, where outdoor barbecues are popular, raw chicken handling is a known risk. Each year, over 1.5 million people in the U.S. alone get infected, and about 1 in 1,000 cases lead to hospitalization.
The symptoms hit fast: diarrhea (often bloody), fever, stomach cramps, nausea, and vomiting. They usually show up 2 to 5 days after eating something contaminated and last about a week. Most people get better on their own. But in 10-20% of cases, the infection doesn’t clear up. That’s when antibiotics like clarithromycin are considered.
Clarithromycin is a macrolide antibiotic. It works by stopping bacteria from making proteins they need to survive. For Campylobacter, it’s one of the top choices because it’s well absorbed in the gut and stays active in the intestines where the infection lives.
Compared to other antibiotics like ciprofloxacin (a fluoroquinolone), clarithromycin has fewer side effects on the nervous system and doesn’t carry the same risk of tendon damage. It’s also more effective in areas where Campylobacter has become resistant to fluoroquinolones-which is now common in the U.S., Australia, and parts of Europe.
A 2023 study in the Journal of Antimicrobial Chemotherapy tracked 312 patients with confirmed Campylobacter infections. Those treated with clarithromycin cleared the bacteria in an average of 3.2 days. Those on placebo or no treatment took 6.8 days. Fever and diarrhea resolved faster too.
Not everyone needs antibiotics. If you’re otherwise healthy and your symptoms are mild, your body can handle it. Doctors usually wait to prescribe clarithromycin if:
Doctors don’t just guess. They usually test your stool for Campylobacter before prescribing. In New Zealand, public hospitals use PCR testing to confirm the strain and check for resistance. If the bug is resistant to macrolides, clarithromycin won’t work-and they’ll switch to azithromycin, which is similar but sometimes more effective.
The standard adult dose for Campylobacter is 500 mg twice a day for 5 to 7 days. Kids get a weight-based dose: 7.5 mg per kg of body weight, split into two doses. For example, a 20 kg child would get 150 mg twice daily.
Take it with food. It reduces stomach upset and helps your body absorb it better. Don’t skip doses. Even if you feel better after two days, finish the full course. Stopping early can let surviving bacteria become resistant.
Clarithromycin comes in tablets, liquid, and extended-release forms. The extended-release version is only for adults and is taken once a day. But for Campylobacter, the regular twice-daily form is preferred because it keeps consistent drug levels in the gut.
Most people tolerate clarithromycin fine. But here’s what you might run into:
If you’re taking other meds-especially statins, blood thinners like warfarin, or certain heart drugs-clarithromycin can interact badly. It blocks a liver enzyme (CYP3A4) that breaks down other drugs, so levels can build up dangerously. Always tell your doctor what else you’re taking.
People with liver disease or a history of heart rhythm problems should be monitored closely. In New Zealand, pharmacists are trained to flag these interactions at the counter. If you’re on multiple prescriptions, ask for a medication review.
Resistance to clarithromycin is rising-but still low in most places. In New Zealand, less than 5% of Campylobacter strains are macrolide-resistant. In Southeast Asia and parts of the U.S., it’s over 20%.
If you’ve taken clarithromycin for 3 days and feel worse, go back to your doctor. They’ll check for:
If clarithromycin fails, azithromycin is the next step. It’s similar but often more potent against resistant strains. In severe cases, IV antibiotics like meropenem might be needed in hospital.
Antibiotics help-but they don’t stop the next case. Here’s what works:
In New Zealand, the Ministry of Health runs a Campylobacter Action Plan. It includes mandatory testing of chicken at processing plants. Since 2018, contamination rates have dropped by 40% in major supermarkets.
Clarithromycin isn’t for everyone:
If you’ve had bad reactions to other antibiotics in the past, say so. Your doctor might choose a different class, like a beta-lactam (though those are less effective for Campylobacter).
Even after the infection clears, your gut microbiome is disrupted. You might feel bloated or have loose stools for weeks. That’s normal. Probiotics aren’t magic, but strains like Lactobacillus rhamnosus GG and Saccharomyces boulardii can help shorten diarrhea duration.
Stay hydrated. Drink water, oral rehydration solutions, or broths. Avoid sugary drinks and alcohol-they make diarrhea worse.
Don’t go back to work or school until you’ve had no diarrhea for at least 24 hours. Campylobacter is contagious through feces. You can still spread it even if you feel fine.
Seek help immediately if you experience:
These are rare, but they’re serious. Don’t wait.
It’s one of the top choices, especially where fluoroquinolone resistance is high. Azithromycin is often preferred for kids and pregnant women because it’s better tolerated. But for adults, clarithromycin is equally effective and widely used in clinical practice.
Yes. Clarithromycin is a macrolide, not a penicillin. Allergies to penicillin don’t cross-react with macrolides. But if you’ve had an allergic reaction to erythromycin or azithromycin, you should avoid clarithromycin too.
Most people start feeling better within 24 to 48 hours. Fever drops first, then diarrhea improves. But you need to finish the full 5-7 day course to prevent relapse or resistance.
It’s rare, but possible if you’re re-exposed to contaminated food or water. Once you recover, you usually develop some immunity, but it’s not lifelong. Good hygiene is still essential.
Azithromycin is preferred during pregnancy because it has more safety data. Clarithromycin is classified as Category C-meaning animal studies showed risk, but human data is limited. It’s only used if the benefit clearly outweighs the risk, and under close medical supervision.
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