Mycophenolate mofetil (MMF) is the 2-morpholinoethyl ester of mycophenolic acid (MPA), one of the several phenol compounds first described by Alsberg and Black in 1913 in cultures of Penicillium stoloniferum . MPA has been found to inhibit DNA synthesis by selectively inhibiting inosine monophosphate dehydrogenase (IMPDH), an enzyme that catalyzes the rate-limiting step in the de novo biosynthesis of guanine nucleotides (reviewed in Ref. ). MPA targets mainly T and B lymphocytes which, unlike other cell types, are dependent almost exclusively on the de novo guanine nucleotide synthesis pathway for proliferation and differentiation. MPA is a fivefold more potent inhibitor of the IMPDH II isoform specific to lymphocytes than of the housekeeping IMPDH I isoform, found in most cell types. MMF inhibits T and B cell proliferation, induces apoptosis of T cells, and inhibits antibody production by B cells.

Besides its antiproliferative effect on lymphocytes, MMF has several other mechanisms of action. Guanosine triphosphate (GTP) depletion caused by MMF impairs fucosylation and surface expression of adhesion molecules of lymphocytes and monocytes, preventing their attachment to endothelial cells during their recruitment to inflammation sites. As monocytes and macrophages are major producers of proinflammatory cytokines causing fibroblast recruitment and proliferation at the inflammation site (such as tumor necrosis factor α and interleukin-1), their depletion reduces production of these cytokines, inhibiting fibroblast proliferation and tissue fibrosis. MPA was shown to inhibit the surface expression of antigens responsible for maturation and efficient antigen presentation by dendritic cells, thereby suppressing immune responses. GTP depletion also impairs inducible nitric oxide synthase (iNOS) activity, which leads to a reduction of the oxidative stress caused by activated monocytes, macrophages, and endothelial cells.

MMF has 94% oral bioavailability. Following absorption MMF is converted to its active metabolite, MPA, by plasma, liver, and kidney esterases. MPA is almost completely inactivated in the liver by glucuronyl transferase, and a significant portion of MPA-glucuronide (MPAG) is secreted into the bile and recycled via enterohepatic recirculation. MPAG is converted back to MPA by β-glucuronidase, found mainly in the epidermis and the gastrointestinal tract. The peak plasma level of the drug is reached in less than 1 hour; the elimination rate is 18 hours. A secondary MPA peak occurs at 6 to 12 hours, due to the enterohepatic circulation. Ninety-seven percent of MPA is albumin bound. Most of the drug is excreted as MPAG in the urine.

The most common side effects of MMF are nausea, vomiting, abdominal cramps, and diarrhea, reported in 12% to 36% of patients. All are dose dependent. Hematologic side effects, also dose dependent and reversible upon discontinuation of the drug, include leukopenia, neutropenia, and thrombocytopenia. There are reports of genitourinary side effects of urgency, frequency, dysuria, and sterile pyuria, which generally resolve with continued drug use. Neurologic complaints (headache, tinnitus, and insomnia), rash, and cardiovascular effects (peripheral edema and hypertension) have also been described. MPA/MMF treatment has been associated with an increased incidence of both bacterial and viral infections (especially herpes zoster and cytomegalovirus ). Of importance, a risk of cytomegalovirus infection has been reported in organ transplant patients given MPA/MMF, concomitantly treated with other immunosuppressive agents. The ability of MMF to induce malignancy is controversial. MMF is expected to be less carcinogenic than azathioprine because it is not incorporated into the DNA and does not cause chromosomal breaks. Some studies reported a dose-dependent increase in the risk of lymphoproliferative malignancy in MMF-treated organ transplant patients, but this finding was not supported in a comparative study of MMF-based and other immunosuppressive regimens in renal transplant patients. In dermatologic literature an early report described 3 cases of malignancy during MMF treatment in psoriatic patients. Subsequently, Epinette and colleagues found no increase in the incidence of cancer in psoriatic patients treated with MMF.

A limited number of cases reports suggested MMF could cause fetal malformations in humans. MMF is classified as pregnancy category D (ie, there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks), and therefore it is recommended to use two different reliable methods of birth control 4 weeks before starting and during MMF therapy, and continue birth control for 6 weeks after stopping MMF.

Several drugs are known to interact with MMF via mechanisms of absorption inhibition (antacids), disruption of enterohepatic recirculation (antibiotics, cholestyramine), albumin binding (phenytoin, salicylic acid), and prevention of kidney tubular secretion of MPA (acyclovir, gancyclovir, probenecid).

MPA was first used in dermatology in the 1970s as an anti-inflammatory agent to treat moderate to severe psoriasis. However, by the end of the decade its use was discontinued owing to its gastrointestinal side effects, increased risk of latent viral infections, and possible carcinogenicity. A decade later MMF, the 2-morpholinoethyl ester of MPA, received approval from the from the Food and Drug Administration as an immunosuppressive agent in renal transplant patients, with studies showing that it had better oral bioavailability than MPA and caused fewer gastrointestinal side effects. Owing to its long-term safety and tolerability, it began to be applied in other fields, including dermatology.

Autoimmune bullous diseases are a group of blistering disorders that share a pathogenetic mechanism of autoantibody production against different epidermal and dermoepidermal junction proteins. High-dose steroids are the traditional first-line treatment, but their multiple and potentially severe side effects with prolonged use have prompted dermatologists to seek alternative or steroid-sparing agents. Today, immunosuppressive agents such as azathioprine, cyclophosphamide, and MMF are widely used in the treatment of these diseases.

The initial evidence of the benefit of MMF for pemphigus stems from several case series, reporting the efficacy of MMF as a steroid-sparing agent.

Enk and Knop combined MMF (2 g/d) with prednisolone (2 mg/kg/d) in 12 patients with pemphigus vulgaris, who had relapsed during azathioprine and prednisolone therapy. Eleven patients responded to this therapy, with no relapses during the 9- to 12-month follow-up period. A similar regimen was applied by Chams-Davatchi and colleagues in 10 patients with pemphigus vulgaris with severe resistant/recurrent disease. The lesions completely cleared in 9 patients by 6 to 16 weeks. Five patients relapsed after MMF discontinuation at 6 months’ follow-up, suggesting MMF should be administered for a longer period to sustain remission. Several years later, a large historical prospective trial was conducted that included 31 patients with pemphigus vulgaris and 11 patients with pemphigus foliaceus, who had relapsed on prednisone therapy or had had adverse effects from previous drug therapy. Treatment with MMF (35–45 mg/kg) combined with prednisone led to complete remission in 71% of the pemphigus vulgaris group and 45% of the pemphigus foliaceus group. Mean time to remission was 9 months, and the remission was maintained throughout the 22 months of follow-up.

Powell and colleagues reported treating 16 refractory pemphigus vulgaris and pemphigus foliaceus patients with MMF (starting at 500 mg/d and increasing as tolerated) and prednisone. Clinically inactive disease was achieved in 7 patients. The much lower doses of prednisone at the time of MMF initiation in this study are noteworthy, and may explain the relatively low rate of clinical remission.

In a prospective study of MMF as first-line treatment, Esmaili and colleagues administered MMF (2 g/d) and prednisolone (2 mg/kg/d) to 31 patients with pemphigus vulgaris, with a 12-month follow-up. MMF was beneficial in 21 patients (67.7%), and its addition made it possible to taper down the prednisolone, suggesting its value as a steroid-sparing agent. A more recent prospective controlled trial was conducted by Beissert and colleagues, who randomized 96 patients with mild to moderate pemphigus vulgaris to receive MMF (2–3 g/d) plus prednisolone or placebo plus prednisolone. At the end of the 52-week follow-up, a similar treatment response rate was observed in the two groups. The patients given MMF showed faster and more durable responses, but this difference may have been attributable to the milder disease of the placebo group, which may not have needed the additional immunosuppressive therapy. In all the aforementioned studies the MMF therapy was well tolerated. The most common side effects were gastrointestinal complaints, lymphopenia, and bacterial and viral infections.

MMF/mycophenolate sodium monotherapy for pemphigus vulgaris has shown variable success in several case series.

Several randomized open-label trials compared the efficacy of MMF as a steroid-sparing agent with other immunosuppressive drugs in patients with pemphigus. Beissert and colleagues treated 40 patients with pemphigus vulgaris or pemphigus foliaceus with methylprednisolone and azathioprine or methylprednisolone and MMF. There was no difference between MMF and azathioprine in efficacy, steroid-sparing effect, or safety profile.

In a random controlled study Chams-Davatchi and colleagues compared 4 treatment regimens in 120 patients with pemphigus vulgaris: prednisolone only, prednisolone and azathioprine, prednisolone and MMF, and prednisolone and intravenous cyclophosphamide pulse therapy. There was no difference in complete remission rate between the groups (70%–80% of patients). All immunosuppressive drugs had a steroid-sparing effect; the most efficacious was azathioprine, followed by pulse cyclophosphamide and then MMF.

A few patients with paraneoplastic pemphigus were reported to benefit from combined immunosuppressive regimens, including MMF and corticosteroids or MMF, corticosteroids, and azathioprine.

Several case reports suggested that MMF, alone or combined with corticosteroids, is effective for the treatment of bullous pemphigoid.

A large, prospective, randomized trial of 73 patients with bullous pemphigoid found MMF to be equally efficacious to azathioprine in inducing disease remission (100%) when combined with corticosteroids. Although the average time to complete remission was shorter in the azathioprine-treated group, the MMF group had less liver toxicity.

Enteric-coated mycophenolate sodium (EC-MPS)/MMF has also been used as a steroid-sparing agent or in combination with dapsone for the treatment of cicatricial pemphigoid. Two retrospective studies addressed the role of MMF in the treatment of ocular cicatricial pemphigoid. Daniel and colleagues reported successful control of eye inflammation at 1 year in 70% of 18 patients treated with MMF and prednisone. Saw and colleagues retrospectively compared various immunosuppressive drugs in 115 patients with ocular cicatricial pemphigoid, and found cyclophosphamide to be more successful (69%) than mycophenolate (59%) in controlling the inflammation. However, mycophenolate had the fewest side effects of all the drugs used in the study.

MMF has shown variable success in individual patients with epidermolysis bullosa acquisita. Similarly, several case reports suggested that MMF and EC-MPS were effective for the treatment of refractory linear IgA disease and linear IgA bullous dermatosis of childhood.

In summary, MMF is an immunosuppressive drug widely used today in multiple fields of medicine, including dermatology. Advantages of MMF include its wide therapeutic index, mild side effects, and lack of major end-organ toxicity. MMF has been successfully applied for the treatment of various autoimmune blistering diseases, including pemphigus, bullous pemphigoid, and cicatricial pemphigoid, mostly as a steroid-sparing agent. According to numerous case series, MMF could be of value in treating refractory disease. The few randomized clinical trials conducted to date of patients with pemphigus and bullous pemphigoid report a similar efficacy for MMF to other immunosuppressants. Large-scale clinical trials are needed to further delineate the value of MMF in this setting.