Genetic variation in aryl N-acetyltransferase results in significant differences in the pharmacokinetic and safety profiles of amifampridine (3,4-diaminopyridine) phosphate.

The clinical use of amifampridine phosphate for neuromuscular junction disorders is increasing. The metabolism of amifampridine occurs via polymorphic aryl N-acetyltransferase (NAT), yet its pharmacokinetic (PK) and safety profiles, as influenced by this enzyme system, have not been investigated. The objective of this study was to assess the effect of NAT phenotype and genotype on the PK and safety profiles of amifampridine in healthy volunteers (N = 26). A caffeine challenge test and NAT2 genotyping were used to delineate subjects into slow and fast acetylators for PK and tolerability assessment of single, escalating doses of amifampridine (up to 30 mg) and in multiple daily doses (20 mg QID) of amifampridine. The results showed that fast acetylator phenotypes displayed significantly lower C max, AUC, and shorter t 1/2 for amifampridine than slow acetylators. Plasma concentrations of the N-acetyl metabolite were approximately twofold higher in fast acetylators. Gender differences were not observed. Single doses of amifampridine demonstrated dose linear PKs. Amifampridine achieved steady state plasma levels within 1 day of dosing four times daily. No accumulation or time-dependent changes in amifampridine PK parameters occurred. Overall, slow acetylators reported 73 drug-related treatment-emergent adverse events versus 6 in fast acetylators. Variations in polymorphic NAT corresponding with fast and slow acetylator phenotypes significantly affects the PK and safety profiles of amifampridine.

Subcutaneous efalizumab is not effective in the treatment of alopecia areata.

BACKGROUND: Alopecia areata (AA) is a T-cell-mediated autoimmune disease. Efalizumab is a T-cell-targeted therapy approved for the treatment of psoriasis. OBJECTIVE: To assess the efficacy and safety of efalizumab in the treatment of moderate-to-severe AA. METHODS: Sixty-two patients were enrolled into this phase II, placebo-controlled trial. The trial consisted of three 12-week periods-a double-blind treatment period, an open-label efalizumab treatment period, and a safety follow-up. RESULTS: There were no statistical differences between treatment groups in percent hair regrowth, quality-of-life measures, or changes in biologic markers of disease severity after 12 or 24 weeks. In both groups, there was an approximately 8% response rate for hair regrowth (at 12 weeks). Efalizumab was well tolerated. LIMITATIONS: Numbers were too small for certain analyses. CONCLUSION: A 3- to 6-month trial of efalizumab was not effective in promoting hair regrowth in this small cohort of patients with moderate-to-severe AA.

Pharmacokinetic-pharmacodynamic-efficacy analysis of efalizumab in patients with moderate to severe psoriasis.

PURPOSE: Efalizumab is a humanized anti-CD11a monoclonal antibody that demonstrated efficacy in the treatment of patients with psoriasis. The objective of this study was to perform a pharmacokinetic (PK)-pharmacodynamic (PD)-efficacy (E) modeling analysis with intersubject variability assessment to increase our understanding of the interaction of efalizumab with CD11a on T cells and consequent reduction in severity of disease in psoriasis patients. METHODS: A total of 6,329 samples from 240 patients in five Phase I and II clinical studies were used in the analysis. For the analysis, plasma efalizumab concentration was used as the PK measurement, the percent of predose CD11a was used as the PD measurement, and the psoriasis area and severity index was used as the measure of efficacy. A receptor-mediated PK/PD model was developed that describes the dynamic interaction of efalizumab binding with CD11a. In the efficacy model, the rate of psoriasis skin production is directly proportional to the amount of free surface CD11a on T cells, which is offset by the rate of skin healing. An additional CD11a-independent component to psoriasis skin production accounted for incomplete response to efalizumab therapy. A Monte Carlo parametric expectation maximization method implemented in the ADAPT II program was used to obtain the estimate of population parameters and inter- and intrasubject variability. RESULTS AND CONCLUSIONS: The final model described the PK/PD/E data in psoriasis patients reasonably well. In addition, simulations using the final model suggested that efalizumab administered less frequently could possibly be more convenient with similar efficacy.

A novel targeted T-cell modulator, efalizumab, for plaque psoriasis.

BACKGROUND: Interactions between leukocyte-function-associated antigen type 1 (LFA-1) and intercellular adhesion molecules are important in the pathogenesis of psoriasis. Efalizumab, a humanized monoclonal antibody, binds to the alpha subunit (CD11a) of LFA-1 and inhibits the activation of T cells. METHODS: In a phase 3, multicenter, randomized, placebo-controlled, double-blind study, we assign 597 subjects with psoriasis to receive subcutaneous efalizumab (1 or 2 mg per kilogram of body weight per week) or placebo for 12 weeks. Depending on the response after 12 weeks, subjects received an additional 12 weeks of treatment with efalizumab or placebo. Study treatments were discontinued at week 24, and subjects were followed for an additional 12 weeks. RESULTS: At week 12, there was an improvement of 75 percent or more in the psoriasis area-and-severity index in 22 percent of the subjects who had received 1 mg of efalizumab per kilogram per week and 28 percent of those who had received 2 mg of efalizumab per kilogram per week, as compared with 5 percent of the subjects in the placebo group (P<0.001 for both comparisons). Efalizumab-treated subjects had greater improvement than those in the placebo group as early as week 4 (P<0.001). Among the efalizumab-treated subjects who had an improvement of 75 percent or more at week 12, improvement was maintained through week 24 in 77 percent of those who continued to receive efalizumab, as compared with 20 percent of those who were switched to placebo (P<0.001 for both comparisons). After the discontinuation of efalizumab at week 24, an improvement of 50 percent or more in the psoriasis area-and-severity index was maintained in approximately 30 percent of subjects during the 12 weeks of follow-up. Efalizumab was well tolerated, and adverse events were generally mild to moderate. CONCLUSIONS: Efalizumab therapy resulted in significant improvements in plaque psoriasis in subjects with moderate-to-severe disease. Extending treatment from 12 to 24 weeks resulted in both maintenance and improvement of responses.

Adhesion molecules as therapeutic targets for autoimmune diseases and transplant rejection.

Inflammatory disorders such as autoimmune diseases and graft rejection are mediated by activated leukocytes, particularly T lymphocytes, which penetrate the inflamed tissue and perpetuate or amplify the immune reaction. In an unstimulated state, leukocytes do not readily adhere to the vascular endothelium. However, inflammatory signals induce the expression of proteins on the endothelial cell surface that promote the adhesion and extravasation of activated immune cells from the circulation into the underlying tissues. Key among these molecules are P- and E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the endothelial cells, and their respective counter receptors, P-selectin glycoprotein ligand-1 (PSGL-1), leukocyte function-associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4), on the leukocytes. In vitro blockade of these molecules inhibits the adhesion of leukocytes. In many cases there is attenuation of leukocyte activation as well. Adhesion blockade in animal models prevents or ameliorates graft rejection and disease severity in autoimmune models. Clinical studies with humanised monoclonal antibodies which interfere with LFA-1/ICAM-1 or VLA-4/VCAM-1 interactions have shown significant efficacy and good safety profiles in autoimmune disease, including psoriasis, multiple sclerosis and inflammatory bowel disease. Thus, adhesion blockade is emerging as a useful therapeutic strategy in several inflammatory settings.