Does Cellcept (Mycophenolate Mofetil) affect thyroid function?

Mycophenolate Mofetil (CellCept) and Thyroid Function

Mycophenolate mofetil (CellCept) does not directly affect thyroid function as part of its known adverse effect profile, though it may indirectly impact thyroid health through its immunosuppressive actions. 1

Mechanism of Action and Primary Effects

• Mycophenolate mofetil (MMF) works by inhibiting inosine monophosphate dehydrogenase, an enzyme critical for the de novo pathway of guanosine nucleotide synthesis, thereby inhibiting T and B lymphocyte proliferation 2
• MMF preferentially affects T and B lymphocytes, which are critically dependent on this pathway for proliferation 2
• Common adverse effects include gastrointestinal disturbances, bone marrow suppression, and increased risk of opportunistic infections 1

Thyroid-Related Considerations

Direct Effects on Thyroid

• Endocrinologic effects listed for mycophenolate include hyperglycemia, cushingoid changes, and hirsutism, but thyroid dysfunction is not specifically mentioned among its known direct toxicities 1
• Unlike some immunosuppressants that have documented effects on thyroid function, mycophenolate is not typically associated with direct thyroid toxicity 1

Indirect Effects on Thyroid Function

• As an immunosuppressant, mycophenolate may mask or modify autoimmune thyroid conditions while patients are taking the medication 3
• There have been case reports of patients developing Graves' hyperthyroidism after discontinuation of immunosuppressive therapy that included mycophenolate, particularly in those with pre-existing thyroid peroxidase (TPO) antibodies 3
• This suggests that mycophenolate may temporarily suppress underlying autoimmune thyroid disease that can manifest when the medication is discontinued 3

Clinical Implications

• Regular monitoring of thyroid function is not specifically required for patients on mycophenolate alone, unlike with some other immunosuppressants 1
• However, in transplant recipients who are on multiple immunosuppressive medications, thyroid function tests are typically monitored as part of routine care 1
• Patients with pre-existing thyroid autoimmunity (positive thyroid antibodies) may need closer monitoring, especially when immunosuppression is reduced or discontinued 3

Special Considerations

• In patients receiving both mycophenolate and calcineurin inhibitors (tacrolimus or cyclosporine), the calcineurin inhibitors may have more significant effects on thyroid function than mycophenolate 1
• Patients transitioning from other immunosuppressants known to affect thyroid function (such as certain tyrosine kinase inhibitors or immune checkpoint inhibitors) to mycophenolate should have their thyroid function monitored during the transition 4
• In contrast to mycophenolate, some immunomodulating drugs like interferon-α and interleukin-2 are known to induce a high incidence of autoimmune thyroid dysfunction 4

Recommendations for Monitoring

• For patients without pre-existing thyroid disease starting mycophenolate, routine thyroid function monitoring is not specifically required based on the medication alone 1
• For patients with known thyroid disease or thyroid antibodies who are starting mycophenolate, baseline thyroid function tests are advisable with periodic monitoring 3
• For patients discontinuing mycophenolate after prolonged use, particularly those with pre-existing thyroid antibodies, monitoring for emergence of thyroid dysfunction in the months following discontinuation may be warranted 3