Cefaclor XR Drug Interactions: What to Avoid and What to Tell Your Doctor

Before starting any antibiotic, it's important to tell your doctor and pharmacist about every medication, supplement, and herbal product you're taking. Cefaclor XR has several clinically meaningful drug interactions. Here's a complete guide to what you need to know.

Does Cefaclor XR Have Any Severe Drug Interactions?

Cefaclor XR has no known severe drug-to-drug interactions with commonly used medications. However, there are several moderate and minor interactions that can affect how the drug works or increase certain risks. Additionally, a few contraindicated combinations with live bacterial vaccines require attention.

Critical: Do Not Use With Live Bacterial Vaccines

Cefaclor XR can inactivate live bacterial vaccines, making them ineffective. These combinations should be avoided:

BCG vaccine (tuberculosis): Contraindicated — wait until your antibiotic course is complete before receiving BCG vaccine

Typhoid vaccine (live oral): Contraindicated — do not take Cefaclor XR and oral typhoid vaccine at the same time

Cholera vaccine: Avoid coadministration — do not give cholera vaccine within 14 days of any oral or parenteral antibiotic

Antacids — Timing Interaction

Antacids containing aluminum or magnesium (such as Mylanta, Maalox, or Gaviscon with aluminum) reduce the absorption of Cefaclor XR. This is especially important given that Cefaclor XR already has strict food requirements for proper absorption.

What to do: Take antacids at least 1 hour before OR 1 hour after taking Cefaclor XR. Calcium-based antacids (like Tums) may be less of an issue, but separating them is still recommended.

Warfarin (Blood Thinners) — Enhanced Anticoagulant Effect

Cefaclor XR may increase the anticoagulant effect of warfarin (Coumadin), potentially raising your INR and increasing bleeding risk. This interaction is thought to occur through disruption of gut bacteria that produce vitamin K, which is needed for blood clotting.

What to do: If you take warfarin, tell your prescriber before starting Cefaclor XR. Your doctor may want to monitor your INR more frequently during your antibiotic course.

Probenecid (Gout Medication) — Increased Cefaclor Levels

Probenecid, commonly used for gout, works by blocking the kidney's ability to excrete certain substances. When taken with cefaclor, probenecid slows the kidney excretion of cefaclor, increasing the drug's blood levels. This could increase both efficacy and the risk of side effects.

What to do: Tell your doctor if you take probenecid. Your doctor may need to adjust your cefaclor dose.

Aminoglycoside Antibiotics — Increased Kidney Risk

If you are also taking aminoglycoside antibiotics (such as gentamicin, tobramycin, or plazomicin), combining them with cefaclor may increase the risk of kidney damage (nephrotoxicity) and hearing problems (ototoxicity). This combination is more commonly used in hospital settings under close monitoring.

What to do: Alert your prescriber to any other antibiotics you are taking. Regular monitoring of kidney function and hearing may be warranted.

Immune Checkpoint Inhibitors (Cancer Treatments) — Reduced Efficacy

Cefaclor may reduce the effectiveness of immune checkpoint inhibitor cancer drugs such as pembrolizumab (Keytruda), nivolumab (Opdivo), cemiplimab (Libtayo), and others. The exact mechanism is unclear, but it is thought to relate to changes in the gut microbiome caused by antibiotics.

What to do: If you are currently receiving immune checkpoint inhibitor therapy for cancer, inform your oncologist before taking any antibiotic, including Cefaclor XR. They may recommend an alternative or extra monitoring.

Chloramphenicol — Reduced Cefaclor Effectiveness

Chloramphenicol, an antibiotic sometimes used for serious infections, may reduce the bactericidal activity of cefaclor through pharmacodynamic antagonism. Using both antibiotics together is generally avoided unless specifically indicated.

Hormonal Birth Control — Minimal Risk, Worth Knowing

Cefaclor, like other antibiotics, may theoretically alter intestinal bacteria that play a role in recycling some forms of oral contraceptives (estrogen-based). Current evidence suggests this effect is minimal for most antibiotics and most women. However, if you're using combined oral contraceptives, using a backup contraception method during and for a few days after your antibiotic course is a conservative precaution.

Lab Test Interference

Cefaclor can cause a false-positive result on certain urine glucose tests (copper reduction tests like Clinitest). If you're diabetic and monitor your urine for glucose, use enzyme-based tests (Clinistix, TesTape) instead. Also inform any lab testing personnel that you are taking cefaclor.

What to Tell Your Doctor Before Starting Cefaclor XR

All prescription medications, including blood thinners, gout medications, cancer treatments, and other antibiotics

All OTC medications, especially antacids (Mylanta, Maalox, Tums)

Vitamins and supplements (including herbal products)

Any upcoming vaccinations (especially live bacterial vaccines like BCG or oral typhoid)

Whether you are pregnant, breastfeeding, or planning to become pregnant

Known allergies to any cephalosporin or penicillin antibiotics

Also see our guide to Cefaclor XR Side Effects: What to Expect and When to Call Your Doctor for a complete picture of what to watch for during your treatment.