Clarithromycin is not a drug you hear about every day, but if you’ve been prescribed it, you know it’s one of the most reliable tools doctors have for fighting stubborn bacterial infections. It’s not a cure-all, but when it’s the right fit, it works fast and effectively-often when other antibiotics don’t. Unlike broad-spectrum drugs that hit everything, clarithromycin targets specific bacteria with precision, making it a go-to for respiratory, skin, and stomach infections that refuse to clear up.

What Clarithromycin Actually Is

Clarithromycin belongs to a class of antibiotics called macrolides. These drugs work by stopping bacteria from making proteins they need to survive and multiply. Think of it like cutting off the factory lines that keep a bacterial invasion going. It doesn’t kill bacteria outright right away-it just makes them unable to grow. Over time, your immune system clears the weakened invaders.

It’s available as tablets, liquid, and sometimes in combination with other drugs. The most common brand names are Biaxin and Klacid, but generic versions are widely used. It’s been around since the early 1990s, and despite newer antibiotics popping up, it’s still in active use because it’s effective, well-tolerated by most people, and works against bacteria that have developed resistance to penicillin and other common drugs.

How Clarithromycin Treats Common Infections

Doctors reach for clarithromycin for several specific infections, each with clear clinical backing:

• Strep throat and tonsillitis - Especially when patients are allergic to penicillin. Clarithromycin is one of the few alternatives that works just as well.
• Sinus infections - When symptoms last longer than 10 days or get worse after initial improvement, clarithromycin is often the next step.
• Pneumonia (community-acquired) - It’s particularly useful for atypical pneumonia caused by bacteria like Mycoplasma pneumoniae or Chlamydophila pneumoniae.
• Skin and soft tissue infections - Including cellulitis and impetigo, especially if caused by Staphylococcus or Streptococcus strains.
• Helicobacter pylori infections - This is one of its most important uses. Clarithromycin is a core part of triple therapy (with amoxicillin and a proton pump inhibitor) to eradicate H. pylori, the bacteria that causes most stomach ulcers.

For H. pylori, treatment usually lasts 7 to 14 days. Studies show that when taken correctly, this combination clears the infection in over 80% of cases. That’s huge-because once H. pylori is gone, ulcers rarely come back.

Why It’s Preferred Over Other Antibiotics

Not all antibiotics are created equal. Penicillin works great for many infections, but about 10% of people have allergies to it. That’s where clarithromycin steps in. It’s also more effective than older macrolides like erythromycin because it’s better absorbed by the body and stays active longer.

Compared to azithromycin, another popular macrolide, clarithromycin has a longer half-life and is often more effective against certain strains of H. pylori and some respiratory bugs. It also penetrates tissues like lung and stomach lining better than many other antibiotics, which is why it’s so useful for infections in those areas.

It’s not first-line for every infection, but when guidelines from the CDC or WHO recommend it-like for H. pylori or certain types of pneumonia-it’s because the evidence is solid. A 2023 meta-analysis in the Journal of Antimicrobial Chemotherapy confirmed that clarithromycin-based regimens remain among the most effective for treating H. pylori in regions where resistance to other drugs is rising.

What to Expect: Side Effects and Risks

Most people tolerate clarithromycin well. But like all antibiotics, it’s not without risks. The most common side effects are mild:

• Upset stomach, nausea, or diarrhea
• Unpleasant taste in the mouth (metallic or bitter)
• Headache or dizziness

These usually go away after a few days. Taking it with food can help reduce stomach upset. But there are rarer, more serious risks:

• Liver problems - Signs include yellowing skin, dark urine, or severe abdominal pain. This is rare but needs immediate attention.
• Heart rhythm changes - Clarithromycin can slightly prolong the QT interval on an ECG. That’s usually not a problem for healthy people, but if you have a history of heart arrhythmias, low potassium, or take certain heart medications (like amiodarone or sotalol), your doctor will avoid it.
• Antibiotic resistance - Overuse leads to resistant strains. In some countries, up to 20% of H. pylori strains are now resistant to clarithromycin. That’s why it’s never prescribed alone for stomach infections-it’s always paired with another antibiotic.
• C. difficile infection - Any antibiotic can trigger this severe diarrhea. If you develop watery or bloody stools after starting clarithromycin, stop taking it and call your doctor.

It’s also important to know: clarithromycin interacts with dozens of other medications. It can raise levels of statins (like simvastatin), blood thinners (warfarin), and even some anti-seizure drugs. Always tell your doctor what else you’re taking.

Who Should Avoid It

Clarithromycin isn’t for everyone. You should avoid it if:

• You’ve had a severe allergic reaction to macrolide antibiotics like erythromycin or azithromycin
• You have a history of liver disease caused by previous antibiotic use
• You’re taking medications that can cause dangerous heart rhythm changes when combined with clarithromycin
• You’re pregnant or breastfeeding-while studies haven’t shown major risks, it’s usually avoided unless the benefit clearly outweighs the risk

Children can take it safely, but the dose is based on weight. It’s not recommended for infants under 6 months unless under strict medical supervision.

How to Take It Right

Getting the most out of clarithromycin means taking it exactly as directed-even if you feel better after two days. Stopping early is one of the biggest reasons bacteria become resistant.

Standard dosing:

• Adults: 250 to 500 mg every 12 hours, for 7 to 14 days depending on the infection
• For H. pylori: Usually 500 mg twice daily for 10-14 days, along with amoxicillin and a PPI like omeprazole
• Children: 7.5 mg per kg of body weight every 12 hours, max 500 mg per dose

Take it with or without food-it’s absorbed either way. But if it upsets your stomach, eat something light first. Don’t crush or break extended-release tablets unless your doctor says it’s okay.

Set phone reminders. Missing doses reduces effectiveness. If you forget one, take it as soon as you remember-unless it’s close to the next dose. Then skip the missed one. Never double up.

What Happens If It Doesn’t Work?

If your symptoms don’t improve after 3-4 days-or if they get worse-you need to follow up. It doesn’t mean the drug failed; it could mean:

• The infection is viral, not bacterial
• The bacteria are resistant to clarithromycin
• You have a different type of infection than originally thought

In cases of H. pylori, if treatment fails, doctors often switch to a different combination, like using metronidazole instead of clarithromycin. Antibiotic resistance testing is becoming more common in hospitals and larger clinics, especially when infections keep coming back.

Long-Term Outlook and Alternatives

Clarithromycin will likely stay in use for years, especially for H. pylori and respiratory infections in penicillin-allergic patients. But resistance is growing. In parts of Asia and Europe, clarithromycin resistance in H. pylori now exceeds 30%. That’s why some guidelines now recommend starting with non-macrolide regimens in high-resistance areas.

Alternatives include:

• Azithromycin - Similar class, shorter course, but less effective for H. pylori
• Amoxicillin - First choice for most infections if no allergy
• Doxycycline - Used for respiratory and skin infections, especially in younger adults
• Metronidazole - Often paired with amoxicillin for H. pylori when clarithromycin resistance is suspected

There’s no universal replacement yet. Clarithromycin’s combination of tissue penetration, safety profile, and proven efficacy keeps it relevant.

Final Thoughts

Clarithromycin isn’t flashy. It doesn’t cure everything. But when used correctly-for the right infection, at the right dose, for the full course-it’s one of the most dependable tools in the antibiotic toolbox. It’s not a first choice for every sore throat or sinus infection. But for stubborn cases, especially when penicillin isn’t an option, it’s often the best solution.

The key is knowing when to use it-and when not to. Antibiotics aren’t magic pills. They’re precise instruments. And clarithromycin, when used wisely, can stop infections before they become serious.