Clarithromycin: What It Treats, Side Effects & Safe Use

Clarithromycin is a macrolide antibiotic doctors use for many bacterial infections. It treats sinusitis, bronchitis, community‑acquired pneumonia, skin and soft tissue infections, and it’s part of some H. pylori eradication plans. It stops bacteria from making proteins they need, so the bugs stop growing and your immune system can finish the job.

How to use clarithromycin and side effects

Adults commonly take 250–500 mg every 12 hours for routine infections. There’s also an extended‑release 500 mg tablet usually taken once daily. For H. pylori, clinicians often prescribe 500 mg twice daily along with a proton‑pump inhibitor and a second antibiotic. Children get weight‑based dosing — don’t guess a pediatric dose; ask the prescriber.

Expect mild stomach upset, nausea, loose stools, or a temporary change in taste. Rare but serious problems include liver injury and irregular heart rhythms (QT prolongation). Some large studies linked clarithromycin to a small increase in cardiac events in people with existing heart disease, so mention any heart problems before you start. If you get severe abdominal pain, jaundice, fainting, or palpitations, seek care fast.

Interactions, resistance, and practical tips

Clarithromycin blocks the liver enzyme CYP3A4. That can raise blood levels of medicines such as simvastatin or lovastatin, colchicine, certain benzodiazepines, and ergot drugs. Mixing clarithromycin with other QT‑prolonging medicines — some antipsychotics, fluoroquinolones, or certain antiarrhythmics — can be dangerous. Always list every prescription, over‑the‑counter drug, and supplement when your clinician asks.

Antibiotic resistance changes which drug is best. In areas with high macrolide resistance, azithromycin or clarithromycin may work poorly, and your provider might choose doxycycline, amoxicillin, or a cephalosporin depending on the infection. For sinus and respiratory infections, culture or local resistance data help guide a safe choice.

Don’t use clarithromycin for viral illnesses like colds or flu. If you’re pregnant, breastfeeding, or have severe liver disease, discuss safer options. Take tablets as directed — extended‑release forms are best taken with food to limit stomach upset. Finish the whole course even if you feel better, and don’t double up after a missed dose; take it as soon as you remember unless the next dose is near.

Store clarithromycin at room temperature away from moisture and heat. Keep out of reach of children. Don’t share your antibiotics — the dose and drug are chosen for one person’s infection. If you buy medicine online, use a licensed pharmacy and a prescription; avoid sites that sell antibiotics without asking for a prescriber. Alcohol doesn’t stop clarithromycin from working, but drinking can increase dizziness or stomach upset, so avoid heavy drinking while on treatment. Watch for severe, persistent diarrhea — that could be C. difficile and needs prompt medical care. Keep list of your medicines handy.

If you notice severe diarrhea (especially with fever or blood), yellow skin/eyes, dark urine, signs of an allergic reaction, fainting, or a racing or irregular heartbeat, get medical attention. For mild side effects, a quick message to your prescriber can help decide if switching antibiotics is safer.