Clarithromycin: what it does and what to watch for

Clarithromycin is a macrolide antibiotic doctors use a lot for chest infections, sinusitis, skin infections, and part of some Helicobacter pylori treatments. It works by stopping bacteria from making proteins they need to grow. That sounds simple, but there are a few important things you should know before taking it.

How clarithromycin is commonly used

For adults the usual dose is 250–500 mg every 12 hours for 7–14 days depending on the infection. There’s a 500 mg extended-release tablet taken once daily. For children, dosing is weight-based (often about 7.5 mg/kg twice daily), but always follow a pediatrician’s instructions. Clarithromycin is also used in combination with other meds to treat H. pylori in stomach ulcers — don’t use it alone for that purpose.

If your kidneys are badly reduced (creatinine clearance <30 mL/min), your doctor may cut the dose or space it out. Never change dose on your own.

Side effects, interactions, and safety tips

The most common side effects are stomach upset, nausea, diarrhea, and a metallic or bitter taste. Some people get headache or mild rashes. More serious but rare problems include liver inflammation, allergic reactions, and heart rhythm changes (QT prolongation) — that last one can be dangerous when combined with other meds that affect heart rhythm.

Clarithromycin blocks the liver enzyme CYP3A4. That means it can raise levels of drugs like simvastatin and some benzodiazepines, and make warfarin or colchicine act stronger. Don’t mix clarithromycin with simvastatin — your prescriber should switch your statin or pause it. Tell your doctor about all meds and supplements you take, especially blood thinners, heart meds, certain antifungals, and some antiarrhythmics.

Pregnancy and breastfeeding: clarithromycin is usually avoided in pregnancy unless there’s no safer option. It passes into breastmilk, so discuss risks and benefits with your provider.

Resistant bacteria are a growing problem. If you’ve used macrolides before or your area has high resistance rates, a doctor might choose a different antibiotic or ask for a culture. Don’t pressure a prescriber for antibiotics if your illness looks viral (most coughs and sore throats are viral).

Practical tips: always finish the full course unless told otherwise; don’t skip doses; take with or without food depending on the product (extended-release tablets usually with food). Store at room temperature in the original container. If you miss a dose, take it when you remember unless it’s almost time for the next one — don’t double up.

Thinking of buying online? Use only reputable pharmacies that require a prescription and show clear contact info. Avoid sites that sell antibiotics without a prescription or at suspiciously low prices.

If you notice severe stomach pain, yellowing skin or eyes, sudden muscle weakness, irregular heartbeat, or a severe rash, stop the drug and seek medical help right away. For mild side effects, call your provider — they may switch you to another antibiotic.

Clarithromycin is useful, but not harmless. Know why you’re taking it, check interactions, and follow the label and your prescriber’s advice. That keeps treatment effective and reduces risks.