What Are the Most Important Drug Interactions with Clarithromycin?

Clarithromycin, a macrolide antibiotic, is a potent inhibitor of the enzyme CYP3A4, which means it can significantly slow the breakdown of many other medications in the body. According to FDA drug labeling, clarithromycin has multiple documented contraindicated interactions—meaning these drug combinations must be avoided entirely—with lipid-lowering agents (lovastatin, simvastatin), immunosuppressants (everolimus), sexual dysfunction agents (flibanserin), and certain gastrointestinal medications. Additionally, clarithromycin carries serious warnings when combined with other drugs that rely on CYP3A4 metabolism, including several statins and diabetes medications. This guide summarizes the FDA-documented interactions you and your healthcare provider should know before starting or continuing clarithromycin therapy.

What Is Clarithromycin and How Does It Work?

Clarithromycin is a macrolide antibiotic used to treat bacterial infections of the respiratory tract, skin, and other tissues. Like other macrolides, it works by inhibiting bacterial protein synthesis, stopping bacteria from multiplying and allowing the immune system to clear the infection.

In the human body, clarithromycin is metabolized by the hepatic enzyme cytochrome P450 3A4 (CYP3A4). However, clarithromycin does not simply pass through this metabolic pathway passively—it actively inhibits CYP3A4 activity. This inhibition is the root cause of many clarithromycin drug interactions. When CYP3A4 is inhibited, other drugs that depend on this enzyme for metabolism accumulate in the bloodstream to higher-than-normal levels. This accumulation can lead to increased side effects, toxicity, or serious adverse events depending on the drug involved and the dose.

This CYP3A4 inhibition property is why clarithromycin appears on FDA contraindication lists for so many medications and why it is classified as a strong CYP3A4 inhibitor in clinical drug interaction databases.

Contraindicated Drug Combinations: Do Not Use Together

The FDA has identified several drug combinations where clarithromycin is absolutely contraindicated—meaning these combinations carry unacceptable risk and should not be used together under any circumstance. The source material supplied does not explain the specific mechanisms beyond CYP3A4 inhibition, but the clinical impact warnings are clear and explicit.

Lovastatin and Simvastatin

According to the FDA drug label for clarithromycin, lovastatin and simvastatin are contraindicated when combined with clarithromycin. The label states: "Clarithromycin may increase the exposure of these drugs by inhibition of CYP3A metabolism, thereby increasing the risk of toxicities from these drugs."

Both lovastatin and simvastatin are HMG-CoA reductase inhibitors (statins) used to lower cholesterol. These drugs undergo extensive CYP3A4-mediated metabolism. When clarithromycin inhibits CYP3A4, blood levels of lovastatin or simvastatin can rise dramatically, raising the risk of statin-related muscle injury (myopathy) and, in severe cases, rhabdomyolysis—a life-threatening breakdown of muscle tissue that can lead to acute kidney injury.

The FDA source record does not provide a specific threshold dose or duration after which the risk becomes unacceptable; the contraindication is categorical. If a patient is taking lovastatin or simvastatin and requires antibiotic therapy, an alternative antibiotic that does not inhibit CYP3A4 should be selected.

Atorvastatin and Pravastatin

While atorvastatin and pravastatin are listed in the same FDA table as lovastatin and simvastatin, they are categorized as "Use With Caution" rather than contraindicated. This distinction is important. Both atorvastatin and pravastatin are also CYP3A4-metabolized statins, but the FDA source material indicates that concomitant use with clarithromycin requires careful monitoring rather than absolute avoidance. The supplied source does not specify monitoring parameters or dose adjustments; consult your healthcare provider for specific guidance on how to safely use these drugs together if necessary.

Fluvastatin

Fluvastatin is listed in the FDA clarithromycin label as "No Dose Adjustment" required, suggesting lower interaction risk compared to other statins. This reflects the fact that fluvastatin is metabolized by CYP2C9 and CYP3A4 to a lesser degree than some other statins. However, it remains on the interaction table and should still be discussed with your pharmacist when clarithromycin is prescribed.

Everolimus

Everolimus is an immunosuppressant and mTOR inhibitor used in organ transplant recipients and certain cancer patients. According to its FDA labeling, clarithromycin is contraindicated because it is a strong CYP3A4 inhibitor. The supplied source indicates the mechanism is "CYP3A4 inhibition" and states clarithromycin "should not be coadministered with everolimus." The source does not detail the specific adverse outcome, but CYP3A4 inhibition would be expected to elevate everolimus levels and increase the risk of immunosuppression-related complications.

Flibanserin

Flibanserin is a serotonin 5-HT1A receptor agonist used to treat hypoactive sexual desire disorder in women. According to its FDA label, clarithromycin is contraindicated. The supplied source specifies the mechanism: "Strong CYP3A4 inhibitor; concomitant use is contraindicated due to increased risk of hypotension and syncope." Flibanserin undergoes CYP3A4 metabolism, and when clarithromycin inhibits this pathway, flibanserin levels rise, increasing the risk of dangerous blood pressure drops and fainting.

Lomitapide

Lomitapide is a microsomal triglyceride transfer protein inhibitor used in patients with homozygous familial hypercholesterolemia. The FDA label for lomitapide states that "Concomitant use of strong CYP3A4 inhibitors (such as... clarithromycin...) with lomitapide is contraindicated." The supplied source record does not provide a specific mechanism beyond the CYP3A4 inhibition classification, but the contraindication is explicit and categorical.

Ezetimibe and Simvastatin Tablets (Fixed Combination)

The FDA label for ezetimibe and simvastatin tablets lists clarithromycin as a strong CYP3A4 inhibitor that is "contraindicated" with this fixed-dose combination. The label notes: "If treatment with... clarithromycin... is unavoidable, therapy with ezetimibe and simvastatin tablets must be suspended during the course of treatment." This reinforces that if clarithromycin therapy is necessary, the statin combination should be discontinued for the duration of antibiotic therapy.

Serious Warnings: Use With Caution or Monitoring Required

Beyond absolute contraindications, clarithromycin carries significant warnings when used with other drugs that depend on CYP3A4 metabolism or that pose additional cardiac or safety risks.

Cisapride (Gastroprokinetic Agent)

Cisapride, a medication used to treat gastroesophageal reflux, is listed as contraindicated in combination with clarithromycin. The FDA source warns that "Concomitant administration of clarithromycin with other drugs can lead to serious adverse reactions, including potentially fatal arrhythmias, and are contraindicated." This arrhythmia risk is a known hazard of macrolide antibiotics and is particularly acute when CYP3A4 inhibition causes cisapride levels to rise.

Immunosuppressants: Cyclosporine and Tacrolimus

Cyclosporine and tacrolimus are calcineurin inhibitors used in transplant recipients. The FDA clarithromycin label states: "There have been spontaneous or published reports of CYP3A based interactions of clarithromycin with cyclosporine" and both drugs are listed as "Use With Caution." The source does not specify monitoring intervals or dose adjustments, but the caution designation indicates that concomitant use is possible with heightened vigilance. Cyclosporine undergoes CYP3A4 metabolism, so clarithromycin-mediated CYP3A4 inhibition could raise cyclosporine levels and increase the risk of nephrotoxicity, neurotoxicity, or infection due to over-immunosuppression.

Diabetes Medications: Nateglinide, Repaglinide, Pioglitazone, and Rosiglitazone

The FDA clarithromycin label lists these hypoglycemic agents as "Use With Caution." The source does not provide specific mechanisms or monitoring recommendations, but several of these agents (nateglinide and repaglinide in particular) undergo CYP3A4-mediated metabolism, so clarithromycin could increase their blood levels and potentiate hypoglycemia risk. Insulin is also listed as "Use With Caution" but is not metabolized by CYP3A4; the caution may reflect general concern about infection management and glucose control during acute illness.

Clarithromycin in H. Pylori Eradication Therapy

Clarithromycin is a key component of standard triple-therapy regimens for Helicobacter pylori eradication, typically combined with a proton pump inhibitor (PPI) and amoxicillin. However, the FDA source material for several PPIs—including lansoprazole, rabeprazole, esomeprazole magnesium, and omeprazole magnesium—contains a notable warning about "Combination Therapy with Clarithromycin and Amoxicillin."

These labels state: "Concomitant administration of clarithromycin with other drugs can lead to serious adverse reactions, including potentially fatal arrhythmias, and are contraindicated." This language is somewhat ambiguous in context, because clarithromycin and amoxicillin together with a PPI form the standard-of-care regimen for H. pylori. The warning appears to be a reference to clarithromycin's general arrhythmia risk rather than a contraindication of the specific triple-therapy regimen. However, the exact interpretation should be confirmed with your prescribing physician or pharmacist, as the FDA source language does not explicitly clarify whether the triple-therapy regimen itself is contraindicated or whether the warning applies only to other concomitant drugs that pose arrhythmia risk.

Hypothetical Scenario: Clarithromycin and Lovastatin

To illustrate how clarithromycin's CYP3A4 inhibition leads to documented contraindication, consider a hypothetical patient taking lovastatin 20 mg daily for cholesterol management. Lovastatin is metabolized almost entirely by CYP3A4. If clarithromycin is started for a respiratory infection, CYP3A4 activity drops sharply. Lovastatin blood levels, which would normally remain stable, begin to accumulate because the enzyme that clears the drug is now inhibited. After several days, lovastatin concentrations may rise several-fold above therapeutic levels, increasing the risk of muscle pain, weakness, and in severe cases, rhabdomyolysis. This is why the FDA classifies the combination as contraindicated: the risk of harm outweighs any benefit of using these specific drugs together. An alternative antibiotic and/or a statin with a different metabolic pathway would be selected instead.

Key Documented Clarithromycin Interactions at a Glance

• Contraindicated: Lovastatin, simvastatin, everolimus, flibanserin, lomitapide, ezetimibe/simvastatin combination, cisapride (due to CYP3A4 inhibition and arrhythmia risk)
• Contraindicated in H. pylori regimens (per PPI labels): Clarithromycin with amoxicillin in combination therapies (though standard triple therapy is widely used—confirm with your provider)
• Use With Caution: Atorvastatin, pravastatin, fluvastatin, cyclosporine, tacrolimus, nateglinide, repaglinide, pioglitazone, rosiglitazone, insulin
• Mechanism: CYP3A4 inhibition leading to accumulation of metabolized drugs and increased toxicity risk
• Additional Risk: Macrolide-class arrhythmia risk, particularly with drugs that prolong the QT interval

Questions to Ask Your Pharmacist or Physician Before Starting Clarithromycin

• "Am I currently taking any statin medications, immunosuppressants, or diabetes drugs? If so, are they safe to use with clarithromycin, or do I need to switch medications?"
• "How long will I be taking clarithromycin, and should my other medications be temporarily stopped during treatment?"
• "What are the signs and symptoms of statin-related muscle injury or other adverse effects I should watch for?"
• "If I'm taking a drug that interacts with clarithromycin, are there alternative antibiotics available that would work for my infection?"
• "Will my liver or kidney function affect how clarithromycin and my other medications interact?"
• "Are there any over-the-counter medications or supplements I should avoid while taking clarithromycin?"

Key Takeaways

• Clarithromycin is a strong CYP3A4 inhibitor, meaning it significantly slows the breakdown of many other medications, potentially causing dangerous drug accumulation.
• FDA drug labeling lists multiple absolute contraindications: lovastatin, simvastatin, everolimus, flibanserin, lomitapide, and ezetimibe/simvastatin—these combinations should not be used together.
• Several statins (atorvastatin, pravastatin) and immunosuppressants (cyclosporine, tacrolimus) carry caution warnings with clarithromycin; close monitoring may be required if use is unavoidable.
• Macrolides, including clarithromycin, carry an inherent risk of cardiac arrhythmias, which is compounded when CYP3A4 inhibition raises levels of other arrhythmia-prone drugs like cisapride.
• Always inform your healthcare provider and pharmacist of all medications, supplements, and herbal products you are taking before starting clarithromycin, and confirm that no contraindicated combinations are present in your medication list.

Sources

• U.S. National Library of Medicine DailyMed (FDA-approved drug labeling)
• FDA Open Data: Drug Product Labeling
• PubMed: National Center for Biotechnology Information Literature Database
• NLM RxNorm: Normalized Naming System for Clinical Drugs

Take Control of Your Medication Safety Today

Drug interactions can be serious and sometimes life-threatening, but they are entirely preventable with proper information and communication. Before starting or stopping any medication—especially an antibiotic like clarithromycin—visit checkdruginteractions.com to enter your complete medication list and check for interactions in real time. Our database is powered by FDA labeling and NIH/NLM data, the same authoritative sources used in this guide. Then confirm all medication decisions with your pharmacist or physician. Your healthcare team is the best resource for personalizing these recommendations to your unique health situation.