Mycophenolate Mofetil

Immunosuppressant Antimetabolite (inosine monophosphate dehydrogenase inhibitor)

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 10-20 mg/kg q12h Duration: Variable; often tapered over months. Initial therapy may be 2-4 weeks before assessing response.
Notes: Start at lower end and titrate based on response and tolerance. Monitor CBC and clinical signs. May be used with corticosteroids initially, then taper steroids.
Cat PO 10-15 mg/kg q12h Duration: Variable; often tapered over months. Initial therapy may be 2-4 weeks before assessing response.
Notes: Cats may have lower bioavailability; monitor for GI upset. Use with caution in renal disease. May be used with corticosteroids initially.
Horse PO 2-5 mg/kg q12h Duration: Variable; often long-term for immune-mediated conditions.
Notes: Limited pharmacokinetic data; monitor for GI effects. May be used with corticosteroids.
Rabbit PO 10-20 mg/kg q24h Duration: Variable; limited evidence.
Notes: Extrapolated from other species; use with caution due to GI sensitivity.
Cattle PO Not established Not established Duration: Not established
Notes: Not recommended for routine use; no approved formulations.
Small Ruminants PO Not established Not established Duration: Not established
Notes: Not recommended for routine use; no approved formulations.
Birds/Poultry PO Not established Not established Duration: Not established
Notes: Not recommended for routine use; no approved formulations.

Clinical Indications & Species Uses

General Indications
  • As an immunosuppressant for various immune-mediated diseases, particularly when glucocorticoids are ineffective or cause unacceptable side effects.
  • As a steroid-sparing agent in chronic inflammatory conditions.
Dog (Canine)
  • Immune-mediated hemolytic anemia (IMHA)
  • Immune-mediated thrombocytopenia (ITP)
  • Immune-mediated polyarthritis (IMPA)
  • Inflammatory bowel disease (IBD) (steroid-sparing)
  • Myasthenia gravis (as adjunctive therapy)
  • Meningoencephalomyelitis of unknown origin (MUO)
  • Systemic lupus erythematosus (SLE)
  • Pemphigus foliaceus and other autoimmune skin diseases
  • Steroid-refractory or steroid-intolerant cases
Cat (Feline)
  • Immune-mediated hemolytic anemia (IMHA)
  • Immune-mediated thrombocytopenia (ITP)
  • Inflammatory bowel disease (IBD) (steroid-sparing)
  • Eosinophilic granuloma complex (as adjunctive)
  • Feline stomatitis (as adjunctive in refractory cases)
  • Non-infectious uveitis (as adjunctive)
Horse (Equine)
  • Immune-mediated keratitis (IMMK)
  • Immune-mediated myositis
  • Equine recurrent uveitis (ERU) (as adjunctive)
  • Pemphigus foliaceus
  • Other immune-mediated dermatopathies
Rabbit & Small Mammals
  • Immune-mediated conditions (rarely used, limited evidence)

Pharmacology & Mechanism of Action

Drug Class: Immunosuppressant | Pharmacological Group: Antimetabolite (inosine monophosphate dehydrogenase inhibitor)

Mechanism of Action: Mycophenolate mofetil (MMF) is a prodrug that is rapidly hydrolyzed to mycophenolic acid (MPA), the active metabolite. MPA is a potent, selective, non-competitive inhibitor of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo synthesis of guanine nucleotides. Lymphocytes rely heavily on this pathway for proliferation, whereas other cell types can use salvage pathways. By depleting guanine nucleotides, MPA inhibits DNA synthesis and proliferation of T and B lymphocytes, thereby suppressing cell-mediated immune responses and antibody production. MPA also induces apoptosis of activated T cells and reduces the expression of adhesion molecules, further dampening inflammatory responses.

Pharmacodynamics: MMF suppresses both humoral and cell-mediated immunity. It inhibits mitogen-induced and mixed lymphocyte reaction-induced proliferation of T and B cells, reduces antibody production, and decreases the generation of cytotoxic T cells. It also downregulates the expression of adhesion molecules (e.g., ICAM-1, VCAM-1) on endothelial cells, reducing leukocyte recruitment to sites of inflammation. In veterinary patients, MMF is used as a steroid-sparing agent or in combination with other immunosuppressants to manage immune-mediated diseases. Its effects are reversible upon discontinuation, and it does not exhibit the broad myelosuppressive effects of other antimetabolites like azathioprine.

⚡ Pharmacokinetics Summary

Absorption: Mycophenolate mofetil is well absorbed after oral administration in most species. In dogs, oral bioavailability is approximately 50-80% (variable). In cats, absorption is lower and more variable, with reported bioavailability around 20-50%. Food may decrease peak concentration but not overall absorption. The prodrug is rapidly converted to MPA by esterases in the gut, liver, and plasma.
Distribution: MPA is extensively bound to plasma albumin (approximately 97% in dogs and cats). It distributes into tissues, with high concentrations in the kidneys, liver, and gastrointestinal tract. It crosses the placenta and is excreted in milk. Volume of distribution is moderate, approximately 0.5-1 L/kg in dogs.
Metabolism: MPA is primarily metabolized in the liver by glucuronidation to the inactive metabolite, mycophenolic acid glucuronide (MPAG). MPAG is excreted in bile and undergoes enterohepatic recirculation, which contributes to secondary peaks in plasma concentration. In dogs, enterohepatic recirculation is significant. In cats, metabolism may be slower, leading to higher MPA concentrations.
Excretion: The primary route of excretion is renal, with approximately 87% of the dose excreted in urine as MPAG. A small amount is excreted in feces via biliary elimination. In animals with renal impairment, MPAG accumulation may occur, but MPA levels are less affected. In hepatic impairment, MPA levels may increase due to reduced metabolism.
Half-Life: Dogs: approximately 8-10 hours (MPA). Cats: approximately 6-8 hours (MPA). Horses: approximately 2-4 hours (MPA).
Bioavailability: Dogs: ~50-80% (variable). Cats: ~20-50% (variable). Horses: ~30-50% (oral).
Protein Binding: Approximately 97% bound to plasma albumin in dogs and cats.

Available Formulations & Strengths

Oral Tablet 250 mg, 500 mg (PO)
Oral Capsule 250 mg (PO)
Oral Suspension (reconstituted) 200 mg/mL (PO)
Injectable Solution (IV) 500 mg/20 mL (25 mg/mL) (IV)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to mycophenolate mofetil or mycophenolic acid
  • Pregnancy (teratogenic in humans; avoid in pregnant animals unless benefits outweigh risks)
  • Lactation (excreted in milk; avoid in nursing animals unless necessary)
  • Severe active infections (due to immunosuppression)
  • Severe renal or hepatic impairment (use with caution; dose adjustment may be needed)
  • Concurrent use with azathioprine (increased risk of immunosuppression and toxicity)
Warnings & Clinical Precautions:
  • Immunosuppression may increase susceptibility to infections, including opportunistic infections.
  • Gastrointestinal side effects (vomiting, diarrhea, anorexia) are common; may be alleviated by dividing doses or administering with food.
  • Monitor complete blood count (CBC) regularly for leukopenia, anemia, or thrombocytopenia.
  • Use with caution in animals with renal or hepatic disease; dose adjustment may be necessary.
  • May cause teratogenic effects; use contraception in breeding animals.
  • Do not crush tablets or open capsules; avoid inhalation of powder. Wear gloves when handling.
  • Live vaccines should not be administered during therapy.
  • May interact with other immunosuppressants; use combination therapy with caution.
  • In cats, monitor for signs of GI upset and adjust dose if needed.
  • In horses, monitor for diarrhea and colitis.

Adverse Effects & Reactions

Common:

  • Vomiting
  • Diarrhea
  • Anorexia
  • Weight loss
  • Leukopenia (dose-dependent)
  • Anemia
  • Thrombocytopenia

Serious / Severe:

  • Severe infections (bacterial, viral, fungal)
  • Bone marrow suppression (pancytopenia)
  • Gastrointestinal ulceration or hemorrhage
  • Hepatotoxicity (elevated liver enzymes)
  • Nephrotoxicity (rare)
  • Sepsis

Rare:

  • Pancreatitis
  • Neurotoxicity (tremors, seizures)
  • Allergic reactions (rash, anaphylaxis)
  • Pulmonary fibrosis (long-term use)
  • Lymphoproliferative disorders (long-term use)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Azathioprine Additive immunosuppression and bone marrow suppression; avoid concurrent use. High
Corticosteroids Additive immunosuppression; may be used together but monitor for increased risk of infections. Moderate
Cyclosporine Additive immunosuppression; may increase risk of infections and lymphoproliferative disorders. Moderate
Antacids containing magnesium or aluminum Decreased absorption of mycophenolate; separate administration by at least 2 hours. Moderate
Cholestyramine Interferes with enterohepatic recirculation, reducing MPA levels; avoid concurrent use. Moderate
Probenecid May increase MPA levels by inhibiting tubular secretion; monitor for toxicity. Moderate
Salicylates (e.g., aspirin) May increase free MPA levels by displacing from protein binding; monitor for toxicity. Mild
Live vaccines Immunosuppression may lead to vaccine-induced disease; avoid live vaccines during therapy. High

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe vomiting and diarrhea
  • Bone marrow suppression (leukopenia, thrombocytopenia, anemia)
  • Gastrointestinal ulceration
  • Infections
  • Sepsis

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce vomiting if recent ingestion and animal is stable. Administer activated charcoal to reduce absorption. Provide fluid therapy for dehydration and electrolyte imbalances. Monitor CBC and serum chemistry closely. Consider use of granulocyte colony-stimulating factor (G-CSF) for severe neutropenia. Antibiotics may be indicated for infections. In severe cases, hospitalization and intensive care may be required.

Food Animal Withdrawal Times

Not approved for food animals in the US. Extra-label use in food animals is prohibited due to lack of withdrawal data and potential for residues. Do not use in animals intended for food.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C, 68-77°F).

Handling & Special Conditions: Protect from moisture. Keep in original container. Oral suspension: store at 2-8°C (refrigerate) after reconstitution; do not freeze. Discard after 60 days.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use (CellCept).

Extra-Label (Off-Label) Use: Mycophenolate mofetil is not FDA-approved for veterinary use. Use in animals is extra-label and must comply with AMDUCA (Animal Medicinal Drug Use Clarification Act) regulations. It is prohibited in food-producing animals due to lack of withdrawal times and potential for residues. For companion animals, a valid veterinarian-client-patient relationship is required.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Mycophenolate mofetil is a valuable immunosuppressant in veterinary medicine, particularly for immune-mediated diseases that are refractory to corticosteroids or when steroid-sparing is desired. It is often used in combination with glucocorticoids initially, then tapered. The drug has a slower onset of action (1-2 weeks) compared to corticosteroids, so it is not suitable for acute crises. Monitoring should include CBC, serum biochemistry, and clinical signs. Gastrointestinal side effects are common, especially in cats; administering with food or dividing the dose may help. In dogs, it is well-tolerated at standard doses. In horses, it is used for immune-mediated ocular and skin diseases, but careful monitoring for diarrhea is essential. Due to its teratogenic potential, avoid use in pregnant animals. Always use with caution in animals with hepatic or renal impairment. The drug is expensive, and compliance may be an issue. Overall, it is a useful addition to the immunosuppressive armamentarium in veterinary practice.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)