indication

For the prophylaxis of organ rejection in patients receiving allogeneic renal transplants, administered in combination with cyclosporine and corticosteroids.

pharmacology

Mycophenolic acid is 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

Mycophenolic acid 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, mycophenolic acid has potent cytostatic effects on lymphocytes. Mycophenolic acid inhibits proliferative responses of T- and B-lymphocytes to both mitogenic and allospecific stimulation. Addition of guanosine or deoxyguanosine reverses the cytostatic effects of mycophenolic acid on lymphocytes. Mycophenolic acid also suppresses antibody formation by B-lymphocytes. Mycophenolic acid 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.

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

Mycophenolic acid is metabolized mainly by glucuronyl transferase to glucuronidated metabolites, predominantly the phenolic glucuronide, mycophenolic acid glucuronide (MPAG). MPAG does not manifest pharmacological activity. The acyl glucuronide minor metabolite has pharmacological activity similar to mycophenolic acid. The AUC ratio of Mycophenolic acid:MPAG:acyl glucuronide is approximately 1:24:0.28 at steady state.

absorption

Bioavailability following oral administration of Myfortic delayed-release tablet ranges from 70-95%

half life

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

drug interactions

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 Mycophenolic acid may decrease. Monitor for increased serum concentrations and toxicity of both agents.