A Cochrane review ¹ included 7 studies with a total of 2908 subjects. Compared with placebo, abatacept increased the achievement of an ACR 50 response (a 50% improvement in tender and swollen joint counts and the same level of improvement in 3 of the 5 following variables: patient and physician global assessments, pain, HAQ (Health Assessment Questionnaire), and acute phase reactants) at one year (RR 2.21, 95% CI 1.73 to 2.82; NNT 5, 95% CI 4 to 7; 3 studies, n=993). Significant improvements in physical function (RR 1.62, 95% CI 1.35 to 1.95; 1 study, n=638) and a reduction in disease activity (RR 4.33, 95% CI 2.84 to 6.59; 1 study, n=638) and pain were found in abatacept-treated patients compared to placebo. Abatacept significantly slowed the radiographic progression of joint damage at 12 months compared to placebo (MD -0.27, 95% CI -0.42 to -0.12; 1 study, n=586), although it is not clear what the clinical relevance of this difference is.

Total adverse events were greater in the abatacept group (RR 1.05, 95% CI 1.01 to 1.08; 5 studies, n=2871). Other harm outcomes were not significant with the exception of a greater number of serious infections at 12 months in the abatacept group (Peto OR 1.91, 95% CI 1.07 to 3.42; 3 studies, n=2214). Serious adverse events were increased when abatacept was given in combination with other biologics (RR 2.30, 95% CI 1.15 to 4.62; 2 studies, n=288).

Comment: The quality of evidence is downgraded by study quality (more than 20% loss to follow up and inadequate intention-to-treat adherence).