Ординатура / Офтальмология / Английские материалы / Dry Eye and Ocular Surface Disorders_Pflugfelder, Beuerman, Elliot Stern_2004

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dermatitis, and occasionally postinfectious conditions. They are the drugs of choice for both prevention and treatment of ocular surface inflammation and allograft rejection. Corticosteroids may be administered either topically, periocularly, or systemically (primarily orally, but also intravenously or intramuscularly). They are among the most effective and rapid ocular immunosuppressants. In general, their potent effects are mediated via nonspecific inhibition of many aspects of the inflammatory response. They inhibit lipid peroxidation and synthesis of prostaglandins by phospholipase A2. Among their multiple biological activities, corticosteroids inhibit inflammatory cytokine and chemokine production, decrease synthesis of matrix metalloproteinases, decrease expression of cell adhesion molecules (e.g., ICAM-1), and stimulate lymphocyte apoptosis. They can also stabilize the lysosomal membranes of polymorphonuclear leukocytes and inhibit chemotaxis and phagocytosis. Activated corticosteroid receptors in the cell nucleus bind to DNA and interfere with transcriptional regulators (e.g., AP-1 and NF-κB) of pro-inflammatory genes [2].

A.Topical and Periocular Steroids

Topical corticosteroids usually have good penetration into the anterior segment of the eye. They provide effective local immunosuppression and are useful in the management of ocular surface inflammation, anterior uveitis, episcleritis, and mild allograft rejection. Prolonged use of topical steroids can lead to adverse effects such as surface toxicity, delayed corneal wound healing, secondary glaucoma, and cataracts. Preservative-free topical corticosteroid preparations circumvent the ocular surface toxicity associated with benzylkonium chloride [3]. Many patients with severe ocular surface disease have concomitant glaucoma, rendering them more susceptible to steroid-induced glaucoma. Topical pressuresparing steroids such as fluorometholone and loteprednol have been used as alternatives for patients with steroid response.

Periocular corticosteroids are useful in the management of scleritis, severe uveitis, and limbal allograft rejection. The periocular route typically results in high local concentrations of corticosteroids in both the anterior and posterior segments of the eye without serious systemic side effects. However, the potential risk for ocular side effects remains high.

B.Systemic Steroids

Systemic steroids are frequently necessary to suppress ocular surface inflammation and for management of patients with limbal allografts. In patients with acute rejection or episodic inflammation, a short course of oral corticosteroids may be

useful for suppression of acute inflammation. In patients with chronic inflammation or rejection, initial treatment with a high oral dose, followed by tapering to a lower oral dose, and long-term maintenance with a low oral dose may be necessary to achieve adequate immunosuppression.

Prednisone is the most commonly used oral corticosteroid, but prednisolone, the active form of prednisone, is often prescribed for patients with liver dysfunction. The initial dose of prednisone typically is 1 mg/kg/day in adults. Methylprednisolone (Medrol; Pharmacia and Upjohn, Peapack, NJ, U.S.A.) dose packs are not expected to be useful in chronic ocular surface inflammation, because of rapid corticosteroid tapering. For immediate control of sight-threatening ocular inflammation or graft rejection, intravenous methylprednisolone sodium succinate (Solu-Medrol; Pharmacia and Upjohn, Peapack, NJ, U.S.A.) can be infused slowly over a period of more than 30 min. The recommended regimen consists of 1 g/day for 3 days followed by oral corticosteroid therapy [4]. If the condition worsens on high-dose prednisone, or if there is an inadequate response after 2–4 weeks, additional immunosuppressive agents should be considered. If chronic oral corticosteroid therapy is needed, some clinicians will convert the prednisone to an alternate-day schedule. Alternate-day dosing has been shown to be an effective strategy to reduce side effects while maintaining clinical efficacy. However, the efficacy of alternate-day dosing for patients with allograft rejection has not been studied.

After a satisfactory response, oral corticosteroids should be slowly tapered and eventually discontinued if possible. Rapid tapering of oral corticosteroids may result in a rebound of the ocular inflammation. In general, when tapering steroids, higher doses can be tapered more rapidly, while lower doses require a slow taper to avoid adrenal insufficiency. Patients should be forewarned not to discontinue corticosteroids abruptly. Stress doses of steroids should be given at the times of major surgeries. If chronic immunosuppression with more than 10 mg/day of prednisone is needed, additional immunosuppressive drugs should be considered. It is prudent to caution the patient that the proper endocrine functions may not return for 6–12 months after tapering off chronic oral corticosteroids.

Even when used for a short term, systemic corticosteroids can produce many adverse effects. Patients should be monitored for infection, hypertension, fluid retention, diabetes mellitus, hyperlipidemia, atherosclerosis, osteoporosis, glaucoma, and cataracts. Other potential side effects include headache, anxiety, psychosis, easy bruising, and poor wound healing. Blood pressure and serum glucose should be monitored regularly, with annual evaluation of bone mineral density and blood cholesterol and lipids. It is recommended that daily supplements of 1500 mg of calcium and 800 IU of vitamin D should be given to patients on chronic oral corticosteroids, particularly during the first 6 months of therapy when the bone mineral density loss is the greatest [5]. Steroid-induced bone loss is a doseand duration-dependent process that is partly reversible after steroids

are discontinued. If bone mineral density studies show osteoporosis, antiresorptive agents such as calcitonin, alendronate, etidronate, or residronate should be prescribed [6].

The incidence of peptic ulcer is not significantly increased in patients treated with oral corticosteroids alone, and routine use of H2 blockers for patients taking prednisone may not be necessary [7,8]. However, most nonsteroidal antiinflammatory drugs are associated with increased risks of gastric irritation and ulceration. The concomitant use of oral corticosteroids and nonsteroidal antiinflammatory drugs can further increase the risk of gastric ulceration and should be minimized. All patients on oral nonsteroidal anti-inflammatory drugs, and particularly those on concomitant oral corticosteroids or those with a history of peptic ulcer or gastroesophageal reflux, should be monitored closely for gastrointestinal complications. Prophylactic therapy with either an H2 blocker (e.g., ranitidine 150 mg q.d. to b.i.d.) or a proton pump inhibitor (e.g., omeprazole 20 mg/day) may be beneficial for these patients.

II. IMMUNOSUPPRESSIVE THERAPY

For severe ocular surface inflammation or limbal allograft rejection, initial immunosuppressive regimens generally include high-dose oral corticosteroids. Once inflammation is adequately controlled, the corticosteroids are either tapered or discontinued. With judicious selection of additional immunosuppressive drugs, many patients with severe ocular surface inflammation will benefit from these agents, either with better control of the inflammation or with less risk of corticosteroid-induced side effects. While corticosteroids are essential for achieving immunosuppression after limbal allograft transplantation, most patients cannot tolerate the high dose needed to prevent graft rejection if used as a single agent. Therefore, more specific and less toxic immunosuppressive drugs should be used as steroid-sparing agents, thereby allowing the patient to achieve adequate immunosuppression with lower doses of steroids for shorter durations.

Immunosuppressive drugs can be grouped as (1) alkylating agents, (2) antimetabolites, (3) T-cell inhibitors, and (4) biologics. The alkylating agents include cyclophosphamide (Cytoxan; Bristol-Myers/Squibb, New York, NY, U.S.A.) and chlorambucil (Leukeran; Glaxo Smith Kline, Middlesex, England). The antimetabolites include azathioprine (Imuran; Faro, Bedminster, NJ, U.S.A.), methotrexate (Rheumatrex; Lederle Laboratories, Wayne, NJ, U.S.A.), mycophenolate mofetil (Cellcept; Roche, Basel, Switzerland), and leflunomide (Arava; Aventis Pharma USA, Parsippany, NJ, U.S.A.). The T-cell inhibitors include cyclosporine (Sandimmune and Neoral; Novartis, Basel, Switzerland; and SangCya; Sangstat, Fremont, CA, U.S.A.), and tacrolimus (Prograf; Fujisawa, Osaka, Japan). The biologics are newly developed immunomodulators.

Since most of these immunosuppressive drugs have slower onset of clinical efficacy (often taking weeks to have an effect), systemic corticosteroids are often used initially because of their immediate anti-inflammatory effect.

A.Cyclophosphamide

Cyclophosphamide (Cytoxan) is a nitrogen mustard alkylating agent. Its active metabolites alkylate purines, and lead to cross-linking of DNA and RNA and eventual cell death [9]. Cyclophosphamide is cytotoxic to both resting and dividing lymphocytes [10]. It suppresses primary and established cellular and humoral immune responses, including delayed-type hypersensitivity, mixed lymphocyte reactions, mitogen-induced and antigen-induced blastogenesis, and production of cytokines.

Cyclophosphamide may be given intravenously or orally at dosages of 1–3 mg/kg/day. Its major side effects include alopecia, anemia, and sterile hemorrhagic cystitis. It is well absorbed and is enzymatically converted by the hepatic microsomal enzymes to multiple metabolites, which are excreted primarily by the kidney [11,12]. One of the metabolites, acrolein, is thought to be responsible for bladder toxicity [13]. Use of 2-mercaptoethane sulfonate can detoxify acrolein and reduce bladder toxicity. Both allopurinol and cimetidine can inhibit hepatic microsomal enzymes and increase the metabolites of cyclophosphamide [11]. Doses should be reduced for patients with renal failure.

Cyclophosphamide is approved as an antineoplastic agent. It has been used in several autoimmune diseases and ocular inflammatory conditions, including rheumatoid arthritis, systemic lupus erythematosus, and vasculitis, especially Wegener granulomatosis [14–23]. Intravenous pulsed cyclophosphamide appears to be less effective than oral daily cyclophosphamide [21,22]. In a clinical trial, cyclophosphamide and corticosteroids were more effective than corticosteroids alone for mucous membrane pemphigoid [24].

The most frequently encountered side effect with cyclophosphamide is bone marrow suppression, which is dose-dependent, reversible, and more common in older patients [25]. Some clinicians prefer lowering the white blood count to a level of 3000–4000 cells/mL to induce a therapeutic effect. Granulocytopenia with an absolute neutrophil count below 1000 cells/mL is associated with an increased risk of sepsis. Therefore, alkylating agents should be discontinued when the white count reaches 2500 cells/mL or lower to avoid this complication. A second serious complication, microscopic hematuria or hemorrhagic cystitis, is uncommon and seen primarily in patients with bladder stasis or inadequate fluid intake. Patients on cyclophosphamide therapy should be encouraged to drink sufficient fluid to minimize toxicity. In the presence of bladder toxicity, cyclophosphamide should be discontinued and therapy switched to an alternative agent such as chlorambucil, because it does not cause bladder toxicity.

Cyclophosphamide is teratogenic and is contraindicated in pregnancy. Other toxicities include ovarian suppression, testicular atrophy, azospermia, alopecia, nausea, and vomiting. Nausea and vomiting can be minimized by antiemetics and, to some degree, by adequate hydration. For oral therapy, a complete blood count and urinalysis should be monitored on a weekly basis initially and at least once monthly when a stable dosing is reached. If hematuria persists after 3–4 weeks of discontinuation, a urology consultation is necessary.

B.Chlorambucil

Chlorambucil (Leukeran) is a slow-acting nitrogen mustard alkylating agent [26]. It substitutes an alkyl group for hydrogen ions in organic compounds and interferes with DNA replication and transcription by cross-linking DNA to protein and by intrastrand cross-linking of DNAs.

Chlorambucil may be started orally at a single dose of 0.1–0.2 mg/kg/ day (6–12 mg/day) and increased to a maximum dose of 18 mg/day. Plasma concentrations are reached in 1 h. It is metabolized in the liver to an active metabolite, phenylacetic acid mustard. Both chlorambucil and phenylacetic acid mustard undergo hydrolysis to inactive compounds that are eliminated in the urine.

Chlorambucil has been used for oncotherapy. It has been used less frequently than cyclophosphamide in rheumatic diseases [27]. However, there is greater published success with chlorambucil for Behcet disease [28–32]. Some studies suggest that long-term drug-free remissions can be achieved after 6–24 months of therapy. Patients typically require concomitant oral corticosteroids initially, and one goal of chlorambucil therapy is to taper and discontinue oral corticosteroids over a period of 2–4 months.

The primary side effect of chlorambucil is reversible bone marrow suppression. Opportunistic infections, particularly viral infections such as herpes zoster, may occur. Similar to cyclophosphamide, chlorambucil is teratogenic and is contraindicated in pregnancy. A complete blood count should be monitored regularly. Chlorambucil is more likely to induce thrombocytopenia than is cyclophosphamide. Irreversible azospermia also complicates its use.

Both cyclophosphamide and chlorambucil can cause secondary systemic malignancies [18,33]. It is prudent to advise patients being treated with alkylating agents of their carcinogenic potential.

C.Azathioprine

Azathioprine (Imuran) is a purine nucleoside analog. Its active metabolite, 6- mercaptopurine, interferes with purine synthesis during DNA replication and transcription [34]. Immunologically, azathioprine reduces the numbers of

peripheral T and B cells [35], mixed lymphocyte reactivity, interleukin-2 synthesis, and IgM production [36].

Azathioprine is administered orally in divided dosages totaling 1–3 mg/kg/day. The dose should be reduced when used with allopurinol, which interferes with the metabolism of 6-mercaptopurine by xanthine oxidase [37]. Azathioprine has been approved for rheumatoid arthritis. Its most common use is in organ transplantation, especially in combination with other agents such as prednisone and cyclosporine. Given its nonspecific nature in blocking DNA synthesis, azathioprine can inhibit the proliferation of actively dividing cells. Therefore, it is most effective if given early in the rejection process, to inhibit proliferation of B and T cells. It is less effective for chronic graft rejection, since most of the lymphocytes have already proliferated. It functions as a steroidor cyclosporine-sparing agent that reduces dosages of those medications and their associated toxicities. It has also been used for mild cases of mucous membrane pemphigoid. Other studies have shown its efficacy in psoriatic arthritis, Reiter syndrome, and systemic lupus erythematosus [38,39].

The most common severe side effect of azathioprine is reversible myelosuppression, which is uncommon when the lower dosage is used. Leukopenia may appear rapidly with the use of this agent. Other side effects include hepatoxicity, gastrointestinal distress, alopecia, stomatitis, and secondary infections. An increased risk of malignancy, especially non-Hodgkin lymphoma, has been reported with its use in renal transplant patients. However, it remains unclear whether the risk is increased in patients with autoimmune diseases [40]. When using azathioprine, complete blood and platelet counts should be monitored every 4–6 weeks. In addition, liver function tests (aspartate aminotransferase and alanine aminotransferase) should be performed every 3 months. When hepatotoxicity occurs (liver enzymes 1.5 times greater than the upper normal limit), the dose should be decreased with reevaluation of the liver enzymes after 2 weeks. Once liver enzymes return to normal, laboratory evaluations can be resumed as above.

D.Methotrexate

Methotrexate (Rheumatrex) is a folic acid analog, which inhibits the conversion of dihydrofolate to tetrahydrofolate by dihydrofolate reductase, metabolism that is important during DNA replication [41]. Similar to azathioprine, methotrexate inhibits rapidly dividing cells, such as leukocytes, and thus has an anti-inflam- matory effect.

Methotrexate is typically administered at a dose ranging from 7.5 to 25 mg (with the most common dose being 15 mg) once per week in a single dose. Although methotrexate is usually given orally, it can be given intramuscularly or subcutaneously to enhance efficacy and minimize side effects. When given

orally, up to 35% may be metabolized by the intestinal flora before absorption, and the absorption decreases as the dose increases. When given parenterally, methotrexate is completely absorbed. Concurrent use of folate at 1 mg/day may reduce the hepatotoxicity and minimize nausea. The full therapeutic effect takes 6–8 weeks to occur [42].

Methotrexate has been used effectively in the management of systemic inflammatory diseases, such as rheumatoid arthritis, juvenile rheumatoid arthritis, psoriatic arthritis, and systemic lupus erythematosus [43]. Methotrexate also is used at higher doses an antineoplastic agent. Several studies have used methotrexate to treat various ocular inflammatory diseases, including uveitis and scleritis in adults and children, with general success [42–46].

Methotrexate is the most common immunosuppressive agent used in children. There is extensive experience regarding its use and relative safety in children with juvenile rheumatoid arthritis [47,48]. It is generally safe and well tolerated. It is metabolized more rapidly in children, and thus, higher doses (on a per-weight basis) are used in children. Methotrexate usually is given to children once weekly at an oral dose of 10–25 mg/M2. Because children are smaller, total weekly doses generally are in the same range as those given to adults (7.5–15 mg/week). Oral absorption is variable in children, and subcutaneous injections may be better tolerated than oral administration in children.

The most serious side effects of methotrexate are hepatoxicity, cytopenia, and interstitial pneumonia. Other common gastrointestinal side effects include stomach upset, nausea, stomatitis, and anorexia. Alopecia and rash occur less commonly. Methotrexate is a teratogen and is contraindicated in pregnancy. Before starting methotrexate, a complete blood count, serum chemistry profile, hepatitis B surface antigen, and hepatitis C antibody should be evaluated. Complete blood count and liver function tests are monitored every 1–2 months. If liver enzymes are greater than twice the normal range on two separate occasions, the dose should be decreased. Abnormal liver function occurs in 15% of patients on methotrexate. Because of its potential hepatotoxicity, patients should be advised to abstain from alcohol consumption while receiving methotrexate.

E.Mycophenolate Mofetil

Mycophenolate mofetil (Cellcept) is a selective inhibitor of inosine monophosphate dehydrogenase that interferes with de-novo guanosine synthesis. In most cells, guanosine synthesis can be maintained through an alternative salvage pathway. However, proliferating lymphocytes require both de-novo and salvage pathways for guanosine synthesis. Thus, mycophenolate specifically inhibits the proliferation of both T and B lymphocytes. It also suppresses antibody synthesis, interferes with cellular adhesion to vascular endothelium, and decreases recruitment of leukocytes to sites of inflammation.

Mycophenolate mofetil is generally used at an oral dose of 1 g twice daily with a maximum dose of 3 g/day. The drug has high oral bioavailability but should be ingested on an empty stomach. It is a pro-drug that is hydrolyzed to mycophenolic acid and excreted by kidney. Mycophenolate mofetil should be used with caution in patients with renal impairment and in those with gastrointestinal disorders, which might affect absorption.

Mycophenolate mofetil has been approved for the prevention of allograft rejection in recipients of renal and cardiac transplantation. Its addition to oral corticosteroids and cyclosporine significantly reduces the occurrence of graft rejection [49,50]. Experience with mycophenolate mofetil as monotherapy for ocular inflammatory disease has been limited [51,52]. For ocular inflammatory diseases, mycophenolate mofetil has been used successfully in combination with other agents, such as oral corticosteroids or cyclosporine. Successful use of mycophenolate for patients with high-risk keratoplasty has also been reported [53]. Although the benefit of mycophenolate in limbal stem cell transplantation has not been conclusively established, it is reasonable to use this agent as an adjunct to corticosteroids and cyclosporine in this group of patients to prevent and treat allograft rejection.

Gastrointestinal symptoms (pain, nausea, vomiting, and diarrhea) are common side effects. Leukopenia, anemia, thrombocytopenia, and opportunistic infections (the most notable being cytomegalovirus and herpes simplex infections) can also seen as a result of the myelosuppression. These side effects are usually mild and respond well to a dosage reduction, or temporary discontinuation. Mycophenolate serum levels are not routinely monitored. It should be remembered that many patients might receive other immunosuppressive drugs in combination with mycophenolate mofetil. During treatment, patients should be monitored with complete blood counts on a weekly basis for 4 weeks and monthly thereafter. After patients have been stable for more than 6 months, blood counts may be checked every 2–3 months. Liver function tests should be performed every 3 months.

F.Leflunomide

Leflunomide (Arava) is an antimetabolite that may have T-lymphocyte specificity. After ingestion, leflunomide is rapidly converted to an active metabolite, which binds to dihydrooratate dehydrogenase, thereby inhibiting pyrimidine synthesis by blocking the production of uridine monophosphate [54]. It can inhibit active T-cell proliferation and has anti-inflammatory effects [55].

The initial loading dose is 100 mg daily for 3 days, followed by the usual dose of 20 mg daily. It is available in 10and 20-mg pills and a 100-mg three-pill pack for the initial loading dose. Leflunomide has been approved recently for treatment of active rheumatoid arthritis in patients inadequately controlled by