Psoriatic arthritis patients treated with Ixekizumab ( Taltz ) for 24 weeks have achieved significant improvements in signs and symptoms of their disease when compared to placebo, while also experiencing significantly less progression of radiographic structural joint damage, reduced disability when performing certain physical functions and improved skin clearance of plaque psoriasis.
Detailed results of the SPIRIT-P1 study were presented during the American College of Rheumatology/Association of Rheumatology Health Professionals ( ACR/ARHP ) Annual Meeting in San Francisco.
During the 24-week, double-blind period of this phase 3 study, patients who had never received a biologic disease-modifying antirheumatic drug ( bDMARD ) were treated with either 80 mg of Ixekizumab once every two weeks or every four weeks ( following a 160 mg starting dose ); Adalimumab ( Humira ) at the approved dose of 40 mg every other week; or placebo. Adalimumab was employed as an active control in the SPIRIT-P1 study and was not powered for comparison with Ixekizumab treatment groups.
In both dosing regimens, Ixekizumab-treated patients demonstrated significant improvements compared with placebo in disease activity of psoriatic arthritis as demonstrated by the proportion of patients achieving an ACR20 response at 24 weeks, the study's primary objective.
Improvements were experienced by Ixekizumab-treated patients as early as one week after treatment initiation.
ACR20 represents at least a 20% reduction in a composite measure of disease activity as defined by the ACR. Other measures included ACR50 and ACR70, which represent 50% and 70% reductions in disease activity.
At 24 weeks, 62% of patients treated every two weeks and 58% of patients treated every four weeks with Ixekizumab achieved ACR20 compared with 30% of placebo-treated patients.
The proportions of Ixekizumab-treated patients who achieved ACR50 when treated every two weeks or every four weeks were 47% and 40%, respectively, compared with 15% of patients treated with placebo.
Furthermore, 34% of patients treated with Ixekizumab every two weeks and 23% of those treated every four weeks experienced a 70% reduction in disease activity. Six percent of patients treated with placebo achieved this level of improvement.
Patients treated with Ixekizumab at both dosing regimens also experienced significantly less radiographic progression of structural joint damage than those treated with placebo, as measured by the change from baseline in the van der Heijde modified total Sharp score ( mTSS ) for psoriatic arthritis at 24 weeks.
Structural joint damage caused by psoriatic arthritis may lead to permanent joint deformity and reduced physical function.
Ixekizumab treatment groups also experienced significant improvements compared with placebo in other key secondary measures, including physical function as assessed using the Health Assessment Questionnaire Disability Index ( HAQ-DI ), and improved skin clearance of plaque psoriasis as measured by the Psoriasis Area and Severity Index ( PASI ), including PASI75, 90 and 100.
A PASI75 score indicates at least a 75% reduction in a patient's plaque psoriasis from the patient's baseline assessment, while PASI90 reflects a 90% reduction and PASI100 represents a 100% reduction, reflecting complete skin clearance.
Efficacy results with Adalimumab compared with placebo during the SPIRIT-P1 study were significant on most measures. At 24 weeks, 57% of patients treated with Adalimumab, the study's active control, achieved ACR20, while 39% and 26% achieved ACR50 and ACR70, respectively.
The incidence of treatment-emergent adverse events ( TEAE ) was greater with Ixekizumab treatment compared with placebo. The most common ( greater than or equal to 4% ) adverse events observed with Ixekizumab treatment were injection site reaction, injection site erythema and nasopharyngitis. These events are consistent with those reported in the phase 3 studies of Ixekizumab for the treatment of moderate-to-severe plaque psoriasis ( UNCOVER 1, 2, 3 ).
Serious adverse events and discontinuation rates due to adverse events were not significantly different between treatment groups.
SPIRIT-P1 is a phase 3 randomized, active- and placebo-controlled study examining the effect of Ixekizumab compared with placebo in patients with active psoriatic arthritis who are bDMARD-naïve.
Patients were required to have an established diagnosis of psoriatic arthritis and active disease for at least six months.
The trial included 417 patients ( stratified 1:1:1:1 ratio for all treatment groups ) with active psoriatic arthritis who had at least three tender and three swollen joints and the presence of at least one disease-related joint erosion of the hand or foot as seen on X-ray or a C-reactive protein ( CRP ) greater than 6 mg/L at screening.
During the study, Ixekizumab-treated patients received a starting dose of 160 mg administered subcutaneously ( SC ), as two 80 mg injections, followed by one of two dosing regimens: either 80 mg administered SC once every two weeks or 80 mg administered SC once every four weeks. Adalimumab at the approved dose of 40 mg SC and regimen of every other week was selected as the active control for comparison with placebo.
The SPIRIT-P1 study will also evaluate the long-term efficacy and safety of Ixekizumab in psoriatic arthritis for up to three years.
Ixekizumab is a monoclonal antibody with high affinity and specificity that binds to and neutralizes the pro-inflammatory cytokine interleukin-17A ( IL-17A ), which research has shown can contribute to autoimmune diseases, including psoriatic arthritis and psoriasis.
Ixekizumab does not bind to cytokines IL-17B, IL-17C, IL-17D, IL-17E or IL-17F and is administered via subcutaneous injection. ( Xagena )
Source: Eli Lilly, 2015