indication

For the prophylaxis of organ rejection in patients receiving allogeneic renal, cardiac or hepatic transplants. Mycophenolate mofetil should be used concomitantly with cyclosporine and corticosteroids.

pharmacology

Mycophenolate mofetil is a prodrug of mycophenolic acid, an antibiotic substance derived from Penicillium stoloniferum. It blocks de novo biosynthesis of purine nucleotides by inhibition of the enzyme inosine monophosphate dehydrogenase. Mycophenolic acid is important because of its selective effects on the immune system. It prevents the proliferation of T-cells, lymphocytes, and the formation of antibodies from B-cells. It also may inhibit recruitment of leukocytes to inflammatory sites.

mechanism of action

Mycophenolate mofetil is hydrolyzed to form mycophenolic acid (MPA), which is the active metabolite. MPA is a potent, selective, uncompetitive, and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), and therefore inhibits the de novo pathway of guanosine nucleotide synthesis without incorporation into DNA. Because T- and B-lymphocytes are critically dependent for their proliferation on de novo synthesis of purines, whereas other cell types can utilize salvage pathways, MPA has potent cytostatic effects on lymphocytes. MPA inhibits proliferative responses of T- and B-lymphocytes to both mitogenic and allospecific stimulation. Addition of guanosine or deoxyguanosine reverses the cytostatic effects of MPA on lymphocytes. MPA also suppresses antibody formation by B-lymphocytes. MPA prevents the glycosylation of lymphocyte and monocyte glycoproteins that are involved in intercellular adhesion to endothelial cells and may inhibit recruitment of leukocytes into sites of inflammation and graft rejection. Mycophenolate mofetil did not inhibit early events in the activation of human peripheral blood mononuclear cells, such as the production of interleukin-1 (IL-1) and interleukin-2 (IL-2), but did block the coupling of these events to DNA synthesis and proliferation.

toxicity

Oral (LD50): Acute: 352 mg/kg [Rat], 1000 mg/kg [Mouse], and >6000 mg/kg [Rabbit]. Possible signs and symptoms of acute overdose could include the following: hematological abnormalities such as leukopenia and neutropenia, and gastrointestinal symptoms such as abdominal pain, diarrhea, nausea and vomiting, and dyspepsia.

biotransformation

Following oral and intravenous dosing, mycophenolate mofetil undergoes complete metabolism to MPA, the active metabolite. Metabolism to MPA occurs presystemically after oral dosing. MPA is metabolized principally by glucuronyl transferase to form the phenolic glucuronide of MPA (MPAG) which is not pharmacologically active. In vivo, MPAG is converted to MPA via enterohepatic recirculation. The following metabolites of the 2-hydroxyethyl-morpholino moiety are also recovered in the urine following oral administration of mycophenolate mofetil to healthy subjects: N-(2-carboxymethyl)-morpholine, N-(2-hydroxyethyl)-morpholine, and the N-oxide of N-(2-hydroxyethyl)-morpholine.

absorption

Rapidly absorbed following oral administration. In 12 healthy volunteers, the mean absolute bioavailability of oral mycophenolate mofetil relative to intravenous mycophenolate mofetil (based on MPA AUC) was 94%. Food (27 g fat, 650 calories) has no effect on the extent of absorption (MPA AUC) of mycophenolate mofetil.

half life

The mean elimination half-life for mycophenolic acid (the active metabolite) ranges from 8-16 hours, while that of the MPAG metabolite ranges from 13-17 hours.

route of elimination

Negligible amount of drug is excreted as MPA (< 1% of dose) in the urine. Most (about 87%) of the administered dose is excreted in the urine as MPAG.

drug interactions

Calcium: Formation of non-absorbable complexes

Iron: Oral iron decreases the absorption of mycophenolate-mofetil

Iron Dextran: Oral iron decreases the absorption of mycophenolate-mofetil

Rifampin: Rifampin may decrease the serum concentration of mycophenolate. Concomitant therapy should be avoided.

Tacrolimus: Tacrolimus may increase the plasma concentration of Mycophenolic acid. Monitor and adjust the dose of Mycophenolate mofetil to the therapeutic range.

Trastuzumab: Trastuzumab may increase the risk of neutropenia and anemia. Monitor closely for signs and symptoms of adverse events.

Valganciclovir: The excretion rates of Valganciclovir and/or Mycophenolate mofetil may decrease. Monitor for increased serum concentrations and toxicity of both agents.