CellCept Drug Interactions: What to Avoid and What to Tell Your Doctor

CellCept (mycophenolate mofetil) has several significant drug interactions that every transplant patient should know. Some interactions reduce CellCept's effectiveness — increasing rejection risk. Others increase CellCept or co-drug levels, raising the risk of side effects. A few interactions are serious enough to warrant avoiding the combination entirely.

This guide covers the most important interactions — but always give your transplant team and pharmacist a complete list of every medication, supplement, and over-the-counter product you take.

Interactions That Reduce CellCept Effectiveness (Dangerous)

These interactions lower the amount of active mycophenolic acid (MPA) in your blood, which can allow your immune system to become more active and increase rejection risk:

Cyclosporine (Neoral, Sandimmune): Cyclosporine inhibits the enterohepatic circulation of MPA, significantly reducing CellCept levels — sometimes by 30–40%. Transplant patients taking both must have this factored into their dosing. If your regimen is switched from cyclosporine to tacrolimus (which does not have this effect), your CellCept dose may need to be reduced to avoid over-immunosuppression.

Cholestyramine (bile acid sequestrant): Cholestyramine (used for high cholesterol or itching from liver disease) binds to MPA in the gut and prevents its reabsorption, substantially reducing drug levels. The combination should be avoided if possible, or CellCept should be dosed at maximum separation from cholestyramine.

Antacids (aluminum and magnesium hydroxide): Common antacids like Maalox and Mylanta can reduce CellCept absorption. If you need an antacid, take it at least 2 hours after your CellCept dose — not at the same time.

Proton pump inhibitors (PPIs): Omeprazole (Prilosec), esomeprazole (Nexium), lansoprazole (Prevacid), and other PPIs increase stomach pH, which can reduce MMF absorption by approximately 25–35% in some patients. The effect is most pronounced with the oral suspension and capsule forms. If you take a PPI, your transplant team should know — and some programs specifically avoid PPIs in CellCept patients.

Certain antibiotics (metronidazole, norfloxacin, ciprofloxacin): Some antibiotics disrupt the gut bacteria that help recirculate MPA through the body (enterohepatic circulation). This can reduce effective MPA levels. If you need an antibiotic course, inform your transplant team so they can monitor for any impact.

Interactions That Increase Toxicity Risk

Acyclovir, valacyclovir, ganciclovir, valganciclovir: These antiviral medications (used to treat herpes, CMV, and other viral infections common in transplant patients) compete with MPA for elimination by the kidneys. When taken together — especially in patients with any degree of kidney impairment — the levels of both drugs can rise, increasing the risk of bone marrow suppression (low white blood cells and platelets).

Diclofenac and other NSAIDs: Some anti-inflammatory drugs can increase MPA levels through competition for renal elimination. NSAIDs are also generally avoided in transplant patients due to their effects on kidney function.

Interactions That Affect Other Medications

Oral contraceptives: CellCept can reduce blood levels of the hormones in birth control pills, making them less effective. Women of childbearing potential taking CellCept must use a second non-hormonal birth control method simultaneously (condom, diaphragm, IUD). This is critically important given CellCept's severe embryofetal toxicity.

Fingolimod and other immunosuppressants: Combining CellCept with other immunosuppressants increases the overall degree of immune suppression, raising the risk of serious infections and malignancies.

Live Vaccines: Never During CellCept Treatment

Live attenuated vaccines are absolutely contraindicated while taking CellCept. Examples include:

Intranasal influenza (FluMist)

MMR (measles, mumps, rubella)

Varicella (chickenpox) and zoster (shingles live vaccine — Zostavax)

Yellow fever

Oral polio (not used in the US but relevant for travel medicine)

Inactivated vaccines (flu shot, COVID-19, hepatitis B, shingles Shingrix, pneumococcal, Tdap) are safe to give but may produce a weaker immune response due to immunosuppression. Update all recommended vaccines before starting CellCept if possible.

Food Interactions

CellCept should be taken on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption. High-fat foods can delay but not significantly reduce absorption of the capsules and tablets. Avoid processed deli meats, which have a higher risk of listeria — a bacterial pathogen particularly dangerous for immunosuppressed patients.

What to Tell Every Healthcare Provider

Any time you see a new healthcare provider — including urgent care, emergency room, dentist, or specialist — tell them you take CellCept. Drug interactions and infection risk considerations affect treatment decisions across all specialties. Keep a current medication card with you at all times listing all your transplant medications.

For a complete overview of CellCept side effects and warning signs to watch for, see: CellCept Side Effects: What to Expect and When to Call Your Doctor.