Differing contribution of methotrexate polyglutamates to adalimumab blood levels as compared with etanercept

Methotrexate (MTX) is known to improve blood levels and clinical outcome to anti-tumour necrosis factor (anti-TNF) therapy by reducing the formation of antidrug antibodies.1 Recent findings indicate that MTX prevents immunisation against TNF inhibitors through de novo purine biosynthesis inhibition and generation of immunosuppressive adenosine.2 This effect is mediated by activation of MTX prodrug to MTX polyglutamates (MTXPG), and we previously...