Efalizumab A Review of its Use in the Management of Chronic Moderate-to-Severe Plaque Psoriasis

Efalizumab (Raptiva (R)) is a recombinant, humanized, monoclonal antibody that targets CD11a, the a-subunit of the heterodimeric lymphocyte surface protein lymphocyte function-associated antigen-1 (LFA-1). It is approved for the treatment of adult patients (aged 18 years) with chronic moderate-to-severe plaque psoriasis who are candidates for systemic therapy or phototherapy (in the US), or who have failed to respond to, have a contraindication to, or are intolerant of, other systemic therapies, including cyclosporine (ciclosporin), methotrexate, and psoralen plus UVA photochemotherapy (in the EU). Weekly subcutaneous injections of efalizumab are effective and generally well tolerated in the treatment of adults with chronic moderate-to-severe plaque psoriasis, including high-need individuals (i.e. those for whom at least two currently available systemic therapies are unsuitable due to lack of efficacy, intolerance, or contraindication), and patients with difficult-to-treat forms of the disease affecting the scalp, hands/feet, or nails. Clinical improvements are maintained, with no evidence of cumulative or end-organ toxicity, during continuous administration of efalizumab for up to 3 years; 4-, 5-, and 7-year safety data are being collected. The therapeutic profile of efalizumab cannot be directly compared with that of other antipsoriasis agents because of a lack of head-to-head comparative studies. Nonetheless, a considerable body of data indicates that efalizumab is an appropriate alternative to other biologic or nonbiologic therapies for the treatment of chronic moderate-to-severe plaque psoriasis that, additionally, offers the potential convenience of self-injection at home. Pharmacologic Properties Efalizumab inhibits the interaction of LFA-1 with its ligand, intercellular adhesion molecule-1, thereby interfering with at least three important events in the T-cell-mediated immunopathology of psoriasis (i.e. initial activation, trafficking, and reactivation of T cells). When subcutaneously administered to patients with chronic moderate-to-severe plaque psoriasis, the pharmacodynamic actions of efalizurnab 1 mg/k-g/week included a rapid, maximal, and reversible down-modulation of CD11a expression and saturation of CD11a binding sites on T cells in the peripheral circulation. The reversible increase in circulating leukocyte and lymphocyte counts induced by efalizurnab at this dose level is consistent with the proposed mechanism of action of the drug. Efalizumab demonstrates dose-dependent nonlinear pharmacokinctics due to its specific and saturable binding to CD11a. At the 1 mg/kg/week dose level, steady-state serum efalizurnab concentrations were achieved after 4 weeks; the mean trough serum efalizurnab concentration was stable during long-term, continuous therapy for up to 3 years. The mean apparent volume of distribution of efalizurnab is 9.13 L. Efalizumab elimination from the serum of psoriasis patients is related to T-cell surface CD11a expression; the drug is cleared through CD11a receptor-mediated internalization and lysozymal degradation. The elimination half-life of efalizurnab at the 1 mg/kg/week dose level ranged from 5.5 to 10.5 days. Therapeutic Efficacy The efficacy of efalizumab as monotherapy has been evaluated in adults with chronic moderate-to-severe plaque psoriasis (e.g. baseline psoriasis area severity index [PASI] score >= 12). A 12-week course of subcutaneous efalizumab 1 mg/kg/week (including an initial conditioning dose of 0.7 mg/kg/week) was superior to placebo in reducing physician-assessed disease severity in five randomized, double-blind, multicenter studies. The proportion of patients who achieved a >= 75% improvement in PASI from baseline (PASI 75) at week 12 (primary endpoint in four studies) ranged from 22% to 38.9% with efalizumab versus 2.4-5% with placebo (p < 0.001). Treatment with efalizumab was also more effective than placebo in improving patient-reported outcomes; these included health-related quality of life (HR-QOL), as assessed using dermatologic-specific and generic instruments, and psoriasis-related cutaneous symptoms. Significant improvements in physician- and patient-assessed endpoints were seen after 2-4 weeks' therapy. In one large study (n = 793), the efficacy of efalizumab in the majority subgroup of 526 subjectively defined 'high-need' patients (i.e. those for whom at least two currently available systemic therapies were unsuitable due to lack of efficacy, intolerance, or contraindication) was similar to that in the total study population. Extending the duration of treatment with efalizumab 1 mg/kg/week from 12 to 24 weeks was associated with further reductions in disease severity as well as maintained improvements in patient HR-QOL and other self-reported outcomes. Similarly, additional or maintained improvements in physician-assessed outcomes were observed when treatment with efalizumab 1 mg/kg/week was continued beyond 12 weeks in the noncomparative CONTROL I and H studies; the latter was a large trial in 1255 evaluable patients who had failed to respond to, had a contraindication to, or were intolerant of, other systemic therapies. Efalizumab therapy was effective in reducing disease severity in subgroups of patients with difficult-to-treat forms of plaque psoriasis affecting the scalp, hands/feet, or nails who were enrolled in these studies. The long-term efficacy of efalizumab has been demonstrated in clinical studies in which the drug has been administered continuously (mostly at a maintenance dosage of 1 mg/kg/week) for up to 3 years. Efalizumab is a suppressive therapy intended for continuous administration. Among patients who achieved a PASI 75 response, 86% experienced psoriasis relapse (after a median time of 67 days), and 14% experienced psoriasis rebound (after a median time of 36 days), following abrupt discontinuation of efalizumab (pooled data). Retreatment with a 12-week course of efalizumab was effective in reducing disease severity in patients who previously discontinued treatment (the response rate in terms of the proportion of patients who achieved a >= 50% improvement in PASI from baseline, or attained a dynamic physician's global assessment rating of good, excellent, or cleared, was approximate to 56%). Tolerability Weekly subcutaneous injections of efalizumab were generally well tolerated. The most common adverse events in patients treated with efalizumab 1 mg/kg/week (includes an initial conditioning dose of 0.7 mg/kg) in 12-week, double-blind, placebo-controlled trials were mild-to-moderate, acute flu-like symptoms (e.g. headache, chills, nausea, myalgia, and fever) that began within 2 days following the first two injections. Most of these events were self-limiting or could be managed with acetaminophen (paracetamol) or NSAIDs. With the exception of the expected reduction in acute flu-like symptoms, the tolerability profile of efalizumab 1 mg/kg/week during long-term maintenance therapy was similar to that during short-term treatment. During continuous treatment for up to 3 years, there was no emergence of new, or increase in the rate of existing, common adverse events, and no evidence of cumulative or end-organ toxicity. Available (predominantly short-term) data from clinical trials suggests that efalizumab does not increase the risk of infection, malignancy, or arthritis-related adverse events. Efalizumab was associated with a higher rate of psoriasis-related adverse events than placebo in the short-term (pooled data); however, the rate of psoriasis-related adverse events either stabilized or gradually declined (to a level similar to that observed with placebo in short-term studies) during long-term treatment in individual studies. Adverse neurologic events (including progressive multifocal leukoencephalopathy) and immune-mediated thrombocytopenia and hemolytic anemia have been reported in patients receiving efalizumab during the clinical development program and/or postmarketing surveillance.