Methotrexate is a folic acid analog that inhibits the conversion of dihydrofolate to tetrahydrofolate and thus has the effect of inhibiting de novo purine synthesis and some transmethylation reactions necessary for synthesis of RNA and DNA. In addition, it causes extracellular release of adenosine, which may have additional anti-inflammatory properties. It is metabolized in the liver and as such has the potential risk of causing significant hepatotoxicity. Methotrexate is given orally weekly medications in the dose range of 7.5–25 mg per week [16, 28, 29]. Oral bioavailability, however, is variable and is associated with significant gastrointestinal irritation at higher dosages. As a result, subcutaneous injection of methotrexate may have better bioavailability and greater therapeutic effect with less gastrointestinal irritation [30]. The onset of action is relatively slow. Methotrexate may take up to 3–6 months to have a full effect on intraocular tissues [28]. It is particularly safe to use in children, as it is associated with no risk of long-term secondary neoplasia. Leukopenia, elevation of liver enzymes, long-term development of cirrhosis and even pulmonary fibrosis are potential complications of methotrexate use. Since methotrexate can affect rapidly dividing cells, it does tend to cause nausea, fatigue, mucous membrane ulceration, and dry eyes symptoms. Folic acid supplementation at 1–2 mg per day usually decreases the severity of side effects [12, 31]. Avoidance of alcohol to reduce hepatotoxicity is essential. Since methotrexate is a category X medication for pregnancy, appropriate dual methods of contraception are required in women of childbearing age. There is also potential for spermatic mutation, and males should be off the drug for at least 4 months prior to attempting conception [12].

There is substantial Level I and II evidence of the efficacy of methotrexate in the treatment of rheumatoid arthritis [6, 8, 32]. In addition there is extensive level II-2 evidence of the efficacy of methotrexate in the management of ocular inflammatory diseases [1, 12, 28]. The SITE study has shown that 66% of patients on systemic methotrexate have no inflammation after 1 year of therapy and nearly 60% are able to reduce maintenance prednisone dosage to less than 10 mg per day [28].

Azathioprine is a purine analog and prodrug, which is converted to 6 mercaptopurine, a competitive inhibitor of purine synthesis. Azathioprine produces its immunosuppressive effect by inhibiting DNA and RNA synthesis and actively dividing cells such as lymphocytes [12]. It is absorbed well orally and typically is given at an oral dose of 1–3 mg/kg per day. It is hepatically metabolized and carries with it some potential risk for hepatotoxicity. Patients who are homozygous for deficiency of thiopurine methyltransferase or TPMT should not be treated with azathioprine since they are at particularly great risk for developing pancytopenia from azathioprine [33]. Patients who are heterozygous for this deficiency may require dose adjustment. The presence of TPMT enzyme deficiency should be part of the pretreatment evaluation of patients who are being considered for azathioprine therapy [33]. Like methotrexate, azathioprine may take up to 6 months to have full therapeutic effect of reducing ocular inflammation. Complications of therapy include nausea, leukopenia with potentially rapid onset of bone marrow suppression particularly in patients who are homozygous for the TPMT mutation, elevation of liver enzymes, and possible increased risk of lymphoma or leukemia [12, 34]. Routine monitoring of complete blood count and liver function tests are essential. Relatively strong level II-2 evidence of the efficacy of azathioprine and ocular inflammatory diseases exists. The SITE study showed that 62% of patients had no inflammation 1 year after initiation of azathioprine, and nearly 50% were able to reduce prednisone maintenance dosing to less than 10 mg per day [34].

Mycophenolate mofetil is a prodrug of mycophenolic acid. It is a selective inhibitor of de novo purine synthesis by selectively and reversibly binding inosine monophosphate dehydrogenase. This enzyme is particularly active in T- and B lymphocytes which are dependent on de novo purine synthesis. This may be the reason why mycophenolate mofetil may have greater efficacy in reducing clonal T_helper and B lymphocyte populations than azathioprine [12]. In addition, mycophenolate suppresses antibody synthesis, interferes with cellular adhesion to vascular endothelium, and reduces recruitment of leukocytes [12]. It is particularly well absorbed when given orally. Therapeutic dosing for adults is usually between 1000 and 3000 mg daily. Unlike azathioprine and methotrexate, mycophenolate mofetil has a slightly more rapid onset of action in ocular tissues. Therapeutic effects may be seen as quickly as 2–3 months after initiation of therapy. Complications of mycophenolate mofetil include gastrointestinal disturbances (most common), leukopenia (rarely red cell aplasia), progressive multifocal leukencephalopathy, and possible increased risk of lymphoma and leukemia [12, 35–37]. It is teratogenic and should be avoided in women of childbearing age who wish to become pregnant. Routine monitoring of complete blood count and liver function tests is required. Gastrointestinal complications such as diarrhea, constipation, or nausea are usually due to inappropriate oral administration of the medication. Mycophenolate mofetil should be given 2–3 h prior to or after meals on an empty stomach. This approach significantly reduces gastrointestinal distress and side effects. In addition dose reductions can also dramatically reduce gastrointestinal side effects. There is strong level II-2 evidence for the use of mycophenolate mofetil in ocular inflammatory disease [12, 36–40]. The SITE studies have shown that 73% of patients treated with mycophenolate mofetil had no inflammation 1 year after initiation of therapy, and 55% were able to reduce prednisone maintenance dosing to less than 10 mg per day [12, 35].

Both cyclosporine and tacrolimus inhibit calcineurin which in turn inhibits nuclear factor of activated T cells resulting in downregulation of the interleukin-2 gene and reduction of interleukin-2 production [12, 41, 42]. This results in a dramatic reduction of the stimulus for T_helper-cell proliferation. These agents are noncytotoxic and selectively and reversibly inhibit helper T lymphocytes-mediated immune responses [41]. These agents do not affect suppressor T cells or T-cell-independent antibody-mediated immunity. Cyclosporine has two different formulations that have different bioavailabilities. Dosing of cyclosporine must be adjusted depending on the formulation used. A modified microemulsion formulation has greater bioavailability than the unmodified cyclosporine A [12]. Cyclosporine does cross the placenta and is found in breast milk. Cyclosporine and tacrolimus should be avoided in pregnancy. Foods and medications such as grapefruit juice, some cholesterol-lowering medications, and macrolide antibiotics increase blood levels of cyclosporine [12]. Cyclosporine has a high risk of causing renal toxicity if given orally at dosages greater than 5 mg/kg per day. Baseline renal and hepatic function tests, serum cholesterol and triglycerides, complete blood count, and blood pressure should be performed along with routine follow-up of these parameters during therapy. Measurements of trough serum levels of cyclosporine are no longer performed. Cyclosporine has a myriad of side effects. Renal toxicity, hypertension requiring therapy, hirsutism, gingival hyperplasia, tremors and paresthesia, acne, headache, nausea, potential increased risk of secondary malignancy, and central nervous system dysfunction or peripheral neuropathies have all been reported [12, 41]. Due to these numerous side effects, Cyclosporine is often used as an adjunctive with other antimetabolites at lower doses to reduce side effects and improve therapeutic efficacy in controlling ocular inflammatory disease. Tacrolimus has less nephrotoxicity and is utilized at an oral dosage of 0.1–0.2 mg/kg per day. Although there is ample clinical evidence of the efficacy of cyclosporine and tacrolimus in the treatment of retinal vasculitis, Behҫet disease, and prevention of organ transplant rejection, mostly anecdotal evidence exists for its efficacy in the treatment of necrotizing scleritis and peripheral ulcerative keratitis [12, 42]. Level II-2 evidence for treatment of ocular inflammatory disease exists for calcineurin inhibitors. The SITE studies showed that 52% of patients had no inflammation 1 year after initiation of cyclosporine or tacrolimus and that 36% were able to reduce prednisone maintenance dosage to less than 10 mg per day [42].

Cyclophosphamide, an alkylating agent, is metabolized following oral administration in the liver to phosphoramide mustard, the active component, and acrolein, a toxic metabolite [12, 27, 43]. Phosphoramide mustard inhibits T- and B-cell proliferation by producing cross-linkage in the DNA between clonidine and thymidine resulting in aberrant base pairing, DNA strand breakage, and interruption of transcription [12]. This results in inhibition of both the resting and actively dividing lymphocytes and suppresses both the cellular and humoral immune responses. Acrolein causes hemorrhagic cystitis but may also have the effect of causing intracellular protein damage [12]. Chlorambucil is also a nitrogen mustard derivative and has a similar mechanism of action although it is slower acting and has a more prolonged effect on inhibition of lymphocyte proliferation. Both drugs are well absorbed orally and are metabolized in the liver. In certain conditions such as necrotizing scleritis, granulomatosis with polyangiitis, relapsing polychondritis, or polyarteritis nodosa, cyclophosphamide is indicated as first-line therapy where it is particularly efficacious in controlling inflammatory ocular disease and also plays a pivotal role in life-saving therapy [27, 44, 45]. Both chlorambucil and cyclophosphamide have been shown to induce long-term remission in patients who have otherwise intractable sight threatening noninfectious uveitis, scleritis, or peripheral ulcerative keratitis [1, 12, 14, 27, 43, 45, 46]. Baseline complete blood count, liver function tests, hepatic function tests, and urinalysis along with routine follow-up evaluation of these parameters are essential. The dosing of cyclophosphamide is typically given orally at 1–3 mg/kg per day over a period of approximately 6 months usually to a maximum cumulative dose of around 35 g. Cumulative dosage greater than 35 g is associated with a substantial increase in secondary leukemia, especially acute myelogenous leukemia in adults [27, 44, 45]. Alternatively, a pulsed intravenous monthly 500 mg dose of cyclophosphamide for 6–12 months can also be given [43]. Oral or intravenous hydration is essential in patients receiving cyclophosphamide therapy. Aggressive hydration can reduce the risk of hemorrhagic cystitis. Chlorambucil may be given as low-dose therapy over 12 months at 0.1–0.2 mg/kg per day orally and dose adjusted to the leukocyte count; or, it may be given as short-term high-dose therapy over 3–6 month period with an initial daily dose of 2 mg per day for 1 week increasing the dose by 2 mg per day each week until inflammation is suppressed or the leukocyte count drops [12, 47]. Unlike other immunomodulatory agents, cyclophosphamide and chlorambucil are dose adjusted based on a target leukocyte count of 3000–4000 cells per microliter off of systemic corticosteroids. The induced leukopenia is proportional to and indicative of the control of inflammatory disease. Complications of cyclophosphamide and chlorambucil include leukopenia, secondary infection especially from Pneumocystis jeroveci (requires Bactrim prophylaxis), hemorrhagic cystitis (cyclophosphamide), permanent infertility from gonadal suppression, pulmonary fibrosis, and significant long-term risk of secondary malignancies of the bladder, skin, leukemia, and lymphoma [12, 27, 43, 44]. These medications are also highly teratogenic. Patients should be advised to use two methods of contraception when these medications are utilized. Due to the relatively high risk of toxicity, these agents are reserved for use by those experienced in the recognition and treatment of potential complications associated with these medications. Strong level II-1 evidence exists for the efficacy of alkylating agents in the treatment of ocular cicatricial pemphigoid [48] and level I and level II-1 evidence exists for the efficacy of these agents in the treatment of systemic vasculitis [1, 3, 27, 43, 47]. The SITE studies demonstrated that 76% of patients treated with alkylating agents had no inflammation 1 year after initiation of therapy and 61% were able to reduce prednisone maintenance dosages to the less than 10 mg per day [27].