Clarithromycin Side Effects: What to Expect and When to Call Your Doctor

Clarithromycin Side Effects: What's Normal, What's Not, and When to Get Help

Clarithromycin (formerly sold as Biaxin) is a macrolide antibiotic prescribed for everything from sinus infections to H. pylori ulcers. Like all antibiotics, it comes with potential side effects — some annoying but harmless, and others that need immediate medical attention.

This guide covers what clinical trials and FDA labeling actually say about Clarithromycin's side effects, so you know what to expect and when to call your doctor.

What Is Clarithromycin? (Quick Overview)

Clarithromycin is a macrolide antibiotic that works by stopping bacteria from making the proteins they need to grow. It's used to treat bacterial infections of the lungs, sinuses, skin, and stomach. It comes as immediate-release tablets (250 mg, 500 mg), extended-release tablets (500 mg), and an oral suspension for children.

A typical course lasts 7 to 14 days, and most people tolerate it well. But side effects do happen — here's what to watch for.

Common Side Effects

These side effects are the most frequently reported in clinical trials. They're usually mild and go away on their own once you finish your course:

• Abnormal or metallic taste (dysgeusia) — This is the most distinctive Clarithromycin side effect. Many patients describe a persistent bitter or metallic taste that lingers between meals. It affects up to 15-20% of patients and resolves after you stop taking the medication.
• Diarrhea — Antibiotics disrupt gut bacteria, and Clarithromycin is no exception. Mild diarrhea is common and usually manageable.
• Nausea — Stomach upset is one of the most common complaints. Taking Clarithromycin with food can help reduce nausea.
• Vomiting — Less common than nausea but still reported, especially at higher doses.
• Abdominal pain or discomfort — Cramping or a general "off" feeling in your stomach is normal during treatment.
• Headache — Reported in clinical trials at rates comparable to placebo in some studies.
• Dyspepsia (indigestion) — A feeling of fullness, bloating, or burning in the upper stomach.

Serious Side Effects

These are less common but require prompt medical attention. Contact your doctor immediately — or go to the emergency room — if you experience any of the following:

Heart Rhythm Problems (QT Prolongation)

Clarithromycin can affect the electrical activity of your heart, leading to a condition called QT prolongation. This can cause dangerous irregular heartbeats (arrhythmias), including a potentially fatal rhythm called torsades de pointes.

Warning signs: Rapid or irregular heartbeat, dizziness, fainting, or feeling like your heart is "fluttering."

Important: In 2018, the FDA issued a safety communication warning about increased risk of heart problems or death in patients with heart disease who took Clarithromycin. If you have any heart condition, make sure your doctor knows before starting this medication.

Liver Damage (Hepatotoxicity)

Clarithromycin can cause liver injury, ranging from mild enzyme elevations to more serious conditions like cholestatic jaundice.

Warning signs: Yellowing of the skin or eyes (jaundice), dark urine, unusual fatigue, upper-right abdominal pain, loss of appetite.

Clostridioides difficile–Associated Diarrhea (CDAD)

All antibiotics can disrupt your normal gut bacteria and allow C. difficile to overgrow, causing severe, watery diarrhea that can become life-threatening.

Warning signs: Watery diarrhea that doesn't stop (more than 3 loose stools per day), fever, abdominal cramping or tenderness, blood or mucus in stool. This can occur during treatment or even weeks after finishing your course.

Severe Allergic Reactions

Anaphylaxis and severe skin reactions like Stevens-Johnson syndrome (SJS) are rare but documented with Clarithromycin.

Warning signs: Hives, swelling of the face/throat/tongue, difficulty breathing, widespread skin rash with blistering or peeling, fever with rash.

Acute Kidney Injury

Kidney problems have been reported, particularly in patients taking other nephrotoxic medications.

Warning signs: Decreased urination, swelling in legs or feet, unusual fatigue, confusion.

Worsening of Myasthenia Gravis

Patients with myasthenia gravis may experience a flare-up of symptoms.

Warning signs: Increased muscle weakness, difficulty swallowing or breathing, drooping eyelids.

Hearing Loss

Reversible hearing loss or ringing in the ears (tinnitus) has been reported, usually at higher doses.

Warning signs: Muffled hearing, ringing or buzzing in the ears, difficulty understanding speech.

Side Effects in Specific Populations

Older Adults

Patients over 65 may be more susceptible to QT prolongation and heart rhythm problems. Kidney function naturally declines with age, which can increase Clarithromycin levels in the blood and raise the risk of side effects.

Children

In pediatric clinical trials, the most commonly reported side effects were diarrhea, vomiting, abdominal pain, and rash. The oral suspension may be better tolerated than tablets. Clarithromycin is not approved for infants under 6 months.

Pregnant or Breastfeeding Women

Clarithromycin is Pregnancy Category C — meaning animal studies showed adverse effects, and there aren't enough human studies to confirm safety. It should only be used during pregnancy if the potential benefit justifies the risk. Clarithromycin is excreted in breast milk, so breastfeeding mothers should discuss alternatives with their doctor.

Patients with Kidney or Liver Problems

If you have severe kidney impairment (CrCl below 30 mL/min), your doctor should reduce your dose or extend the dosing interval. Patients with liver disease should be monitored closely, as Clarithromycin is processed by the liver.

How to Manage Common Side Effects

Most mild side effects can be managed with simple strategies:

• Metallic taste: Suck on sugar-free mints or hard candies between doses. Brushing your teeth more frequently and staying hydrated can also help. This side effect disappears once you finish your course.
• Nausea and stomach upset: Take Clarithromycin with a meal or snack. Extended-release tablets (Clarithromycin ER) must be taken with food anyway, and this helps with nausea for all forms.
• Diarrhea: Stay hydrated. Eat bland foods (bananas, rice, toast). Probiotics may help restore gut bacteria — ask your doctor or pharmacist for recommendations. Do not take anti-diarrheal medications like loperamide without asking your doctor first, as they can mask serious complications like C. difficile infection.
• Headache: Over-the-counter pain relievers like Acetaminophen (Tylenol) are generally safe to take alongside Clarithromycin. Avoid dehydration.

What NOT to Do

• Don't stop your antibiotic early because of mild side effects. Incomplete courses can lead to antibiotic resistance and recurring infections.
• Don't double up on doses if you miss one. Take the missed dose as soon as you remember, unless it's almost time for your next dose.
• Don't take antacids at the same time as Clarithromycin without checking with your pharmacist.

When to Call Your Doctor

Call your doctor promptly if you experience:

• Diarrhea that is severe, watery, or bloody
• Signs of an allergic reaction (hives, swelling, difficulty breathing)
• Yellowing of skin or eyes
• Irregular heartbeat, fainting, or dizziness
• Hearing changes or ringing in your ears
• Dark urine or significantly decreased urination
• Any side effect that feels severe or doesn't improve

If you experience difficulty breathing, chest pain, or severe swelling, call 911 or go to the nearest emergency room.

Final Thoughts

Clarithromycin is an effective antibiotic for a wide range of infections, and most people complete their course without serious problems. The metallic taste is probably the most annoying side effect you'll encounter — and it goes away once you're done.

The key is knowing the difference between "uncomfortable but normal" and "call your doctor now." If you're not sure, err on the side of calling. That's what your doctor is there for.

Looking for more information? Read our full guide on what Clarithromycin is and how to take it, or check Clarithromycin drug interactions to make sure your other medications are compatible.