Clarithromycin Drug Interactions: A Complete Guide to What You Need to Avoid

Clarithromycin is an effective antibiotic, but it has more drug interactions than almost any other commonly prescribed antibiotic. Some of these interactions are inconvenient. Others are genuinely dangerous — even potentially fatal.

This guide covers the interactions you need to know about, in plain language, so you can have an informed conversation with your doctor and pharmacist.

How Drug Interactions Work With Clarithromycin

To understand why Clarithromycin causes so many interactions, you need to know one thing: it's a strong inhibitor of CYP3A4.

CYP3A4 is a liver enzyme responsible for breaking down roughly 50% of all medications on the market. When Clarithromycin blocks this enzyme, other drugs that rely on CYP3A4 for metabolism can build up in your blood to dangerously high levels — as if you'd taken an overdose of those drugs.

Clarithromycin also inhibits a transporter called P-glycoprotein (P-gp), which affects how certain drugs are absorbed and eliminated. This adds another layer of interaction potential.

This is the main reason Clarithromycin has more drug interactions than its cousin Azithromycin — Azithromycin barely affects CYP3A4.

Medications That Interact With Clarithromycin

Contraindicated (Do NOT Take Together)

These combinations are considered too dangerous to use. Your doctor should never prescribe Clarithromycin if you're taking any of these:

• Pimozide (Orap) — An antipsychotic. Combining with Clarithromycin can cause fatal cardiac arrhythmias.
• Cisapride — A GI motility drug. Risk of severe QT prolongation and life-threatening heart rhythm problems.
• Ergotamine and Dihydroergotamine (Migranal, D.H.E. 45) — Migraine medications. Clarithromycin can cause ergotism — a serious condition involving restricted blood flow to extremities.
• Lovastatin (Mevacor) and Simvastatin (Zocor) — Cholesterol-lowering statins. Clarithromycin dramatically increases their levels, leading to risk of rhabdomyolysis (severe muscle breakdown that can cause kidney failure).
• Lomitapide (Juxtapid) — A lipid-lowering drug. Contraindicated with strong CYP3A4 inhibitors.
• Colchicine (in patients with kidney or liver impairment) — Used for gout. Fatal Colchicine toxicity has been reported when combined with Clarithromycin in patients with impaired organs.

Major Interactions (Use With Extreme Caution)

These combinations require close monitoring, dose adjustments, or may warrant switching to a different antibiotic:

• Warfarin (Coumadin, Jantoven) — Blood thinner. Clarithromycin increases Warfarin's anticoagulant effect, raising bleeding risk. INR monitoring is essential.
• Carbamazepine (Tegretol) — Seizure medication. Clarithromycin can increase Carbamazepine levels to toxic ranges, causing dizziness, double vision, and ataxia.
• Cyclosporine (Neoral, Sandimmune) — Immunosuppressant used in transplant patients. Risk of nephrotoxicity (kidney damage) from elevated Cyclosporine levels.
• Digoxin (Lanoxin) — Heart medication. Clarithromycin increases Digoxin levels via P-glycoprotein inhibition, risking toxicity (nausea, visual disturbances, dangerous heart rhythms).
• Theophylline (Theo-24, Elixophyllin) — Asthma/COPD medication. Increased levels can cause seizures, nausea, and rapid heart rate.
• Benzodiazepines — Midazolam (Versed), Triazolam (Halcion) — Sedatives. Clarithromycin can dramatically increase their levels, causing prolonged and excessive sedation.
• Colchicine (in patients with normal organ function) — Even without kidney or liver problems, dose reduction is needed. Monitor for Colchicine toxicity symptoms: muscle weakness, GI distress, low blood counts.

Moderate Interactions (Monitor Closely)

These combinations may need dose adjustments or extra monitoring:

• Calcium channel blockers — Amlodipine (Norvasc), Diltiazem (Cardizem), Verapamil (Calan). Risk of low blood pressure (hypotension) and swelling.
• Atorvastatin (Lipitor), Pravastatin (Pravachol) — While not contraindicated like Lovastatin/Simvastatin, use with caution. Risk of muscle injury. Use the lowest effective statin dose.
• Sildenafil (Viagra), Tadalafil (Cialis) — Clarithromycin increases their levels. Risk of excessive effects including dangerous drops in blood pressure.
• Oral hypoglycemics (diabetes medications) — Risk of hypoglycemia (dangerously low blood sugar). Monitor blood glucose more closely.
• Fluconazole (Diflucan) — An antifungal that can increase Clarithromycin levels in your blood.
• Rifabutin (Mycobutin) — Used for tuberculosis and MAC. Bidirectional interaction: increased Rifabutin toxicity and decreased Clarithromycin efficacy.
• Atazanavir (Reyataz), Ritonavir (Norvir) — HIV medications. Bidirectional interaction that affects levels of both drugs.

Supplements and Over-the-Counter Medications to Watch

Drug interactions aren't limited to prescription medications. Watch out for these:

• St. John's Wort — This herbal supplement induces CYP3A4 (the enzyme Clarithromycin inhibits), potentially reducing Clarithromycin's effectiveness.
• Antacids — While not a dangerous interaction, taking antacids at the same time as Clarithromycin may affect absorption. Space them apart if possible.
• OTC sleep aids containing antihistamines — Combined with Clarithromycin's potential to increase sedation from certain drugs, use caution.
• Supplements containing magnesium or calcium — May interfere with absorption if taken simultaneously.

Food and Drink Interactions

• Grapefruit and grapefruit juice — Grapefruit inhibits CYP3A4 (same enzyme Clarithromycin inhibits), which could further increase drug levels. While the clinical significance with Clarithromycin itself is limited, it could amplify interactions with other medications you're taking.
• Alcohol — Both Clarithromycin and alcohol are processed by the liver. Combining them increases the risk of liver-related side effects and may worsen nausea and GI symptoms.
• Food and extended-release tablets — Clarithromycin ER must be taken with food for proper absorption. This isn't a harmful interaction — it's a requirement.

What to Tell Your Doctor Before Starting Clarithromycin

Before your doctor prescribes Clarithromycin, make sure they know about:

1. Every medication you're currently taking — Prescription drugs, OTC medications, and herbal supplements. Don't leave anything out.
2. Any heart conditions — History of irregular heartbeat, QT prolongation, or heart disease. The FDA issued specific warnings about Clarithromycin use in heart disease patients.
3. Kidney or liver problems — These affect how Clarithromycin is processed and can dramatically increase interaction risks.
4. Allergies — Especially to macrolide antibiotics (Clarithromycin, Azithromycin, Erythromycin).
5. Pregnancy or breastfeeding — Clarithromycin is Pregnancy Category C and passes into breast milk.

Your pharmacist is also an excellent resource. When you fill your prescription, they'll run an interaction check — but this only works if your pharmacy has a complete list of your medications. If you use multiple pharmacies, let each one know what you're taking.

What If You're Already Taking a Medication That Interacts?

Don't panic, and don't stop any medication without talking to your doctor. Your doctor has several options:

• Switch to a different antibiotic with fewer interactions (like Azithromycin)
• Temporarily adjust the dose of the interacting medication
• Temporarily pause a medication during your Clarithromycin course
• Add monitoring (blood tests, EKG) to catch problems early

Final Thoughts

Clarithromycin is an effective antibiotic, but its interaction profile demands respect. The CYP3A4 inhibition is the root cause of most problems, and it's why your doctor and pharmacist need a complete picture of what you're taking.

The good news: these interactions are well-documented and manageable when your healthcare team knows what you're on. The key is communication — before you start Clarithromycin, not after.

For more on this medication, read our guides on what Clarithromycin is, how it works, and how to save money on your prescription.