Efficacy and Safety of Prurisol Administered Orally for Active Moderate to Severe Chronic Plaque Psoriasis

This study is designed as a randomized, double blind, parallel group, placebo-controlled trial to study the efficacy and safety of two oral doses of Prurisol administered twice daily for twelve weeks to subjects with moderate to severe chronic plaque psoriasis. Approximately 189 study participants will be enrolled. Subjects will be randomly assigned to one of three treatment groups in a 3:3:1 randomization ratio, respectively. * Group A (n=81): Prurisol 150 mg bid * Group B (n=81): Placebo * Group C (n=27): Prurisol 200 mg bid Outpatient subjects with moderate to severe chronic plaque psoriasis who are candidates for systemic therapy or phototherapy will be recruited to the study. Study participants are required to have a Psoriasis Area and Severity Index (PASI) score ≥ 12, body surface area involvement ≥ 10%, and a static Physician's Global Assessment (sPGA) of moderate or severe (score of 3 or 4). A subject studied under this clinical protocol will commence with a screening period of up to 4 weeks, a treatment period of 12 weeks, and a follow-up period of 4 weeks ending with an End of Study evaluation. During treatment, subjects will return to the study center every 2 weeks. Efficacy assessments, including physician and patient rated endpoints, will be measured throughout the study. Safety and tolerability will be assessed by ascertainment of AEs and results of clinical laboratory testing, vital signs assessments, and need for concomitant medications. At a subset of sites, blood samples for determination of plasma concentrations of Prurisol (abacavir glycolate) and abacavir, it's metabolite, will be obtained from subjects who consent to provide these samples. At selected sites, for those subjects consenting to photography, standardized digital photographs will be obtained for illustrative purposes.