As the benefits of a top-down approach are countered by the cost and risks of adverse events, more emphasis is placed on identifying predictors of aggressive disease or using a rapid step-up strategy. Patient age under 40, stricturing disease, weight loss, corticosteroid requirement at presentation and perianal disease have all been suggested as indicators of severe disease.47,48 Loss of response.  While the anticipated duration of therapy with biological agents is often Palbociclib undefined, loss of response occurs in approximately 13%

of patients per year of treatment.49 Drug trough levels have been proposed as a predictor of continued response, or to explain the cause of loss of response.50 Neutralizing antibodies to anti-TNF agents can result in reduction in trough levels, and subsequent non-response. Anti-drug antibodies may also be associated with injection site and infusion reactions. The rheumatological literature reports a progression from decreasing trough levels to detection of anti-drug antibodies and finally a loss of response.51 Anti-drug

antibodies are seen in 9–28% of those treated with infliximab,5 and 3–17% of those treated with adalimumab.25,50,52 They occur more frequently with intermittent anti-TNF therapy.53 Co-administration with BGB324 a second immunosuppressive agent reduces the risk of antibody development.54 Strategies to prevent their development include scheduled maintenance therapy and co-administration of corticosteroids or other immunomodulators (see below). With decrease in response, dose intensification,

decreased dosing interval, re-induction or drug switching can be performed.20,27,55–57 Only the latter two approaches are government subsidized in Australia.58 Evidence relating to anti-drug antibodies to trough levels and a loss of response is at times unclear.50 It is unknown which (if any) strategies to maintain trough levels will 上海皓元 result in prolonged clinical effect. Anti-TNF agent trough level, and anti-drug antibody measurement is not widely available at present. Treatment failure.  Treatment failure comprises primary non-response, adverse drug reactions and loss of response. It occurs in up to 50% of those on scheduled maintenance therapy.48 Enrollment in trials of new therapeutic agents such as ustekinumab and vedolizumab, and surgery remain options for failure of existing biological agents. Switching.  Changing anti-TNF agents secondary to treatment failure or loss of response is an accepted therapeutic maneuver. The efficacy of adalimumab59–63 and certolizumab pegol64 in those with loss of response or treatment failure prior to biological therapy has been shown in open label studies, while the success of adalimumab in this setting has been demonstrated in a placebo-controlled trial.56 Switching to a third anti-TNF agent following failure of the two other anti-TNF agents is safe and effective.