ustekinumab is a fully human monoclonal antibody directed against the p40 subunit shared by interleukin 12 and interleukin 23 two naturally occurring protein regulators that play an important role in immune mediated inflammatory diseases including psoriatic arthritis psa in september of 2009 the us fda approved ustekinumab for the treatment of adult patients with moderate to severe plaque psoriasis beginning in november of 2009 janssen biotech formerly centocor biotech the developer of ustekinumab initiated clinical trials to investigate the efficacy of ustekinumab in the treatment of other inflammatory disorders including psa phase ii and phase iii studies showed both a good safety profile and significant efficacy for ustekinumab in the treatment of psa leading to the drug s approval in both europe and the usa in an immunotherapy market currently dominated by anti tnf α drugs for the treatment of psa ustekinumab offers an alternative option for patients with psa including those unresponsive to methotrexate and the tnf α inhibitory agents currently approved for this potentially debilitating disease.