Abstract
BackgroundTo get insight in the prevalence of high, or low/no serum infliximab trough levels in patients with low disease activity and if serum trough levels are stable and reliable longitudinally we conducted a prospective cohort studyMethodsIn a longitudinal, observational cohort of RA patients treated with infliximab for at least 6 months, treatment interval, DAS28, infliximab trough levels and anti-infliximab antibodies were assessed. Prevalence of low (<1 mg/l) and high (>5 mg/l) infliximab serum trough levels and anti-infliximab antibodies was recorded. Relationship of a change in anti-infliximab antibodies and treatment interval was described. Reliability of consecutive infliximab serum trough levels and anti-infliximab antibodies in patients with stable DAS28 and treatment was analysed with Spearman correlation and kappa-analysis.Results147 patients with a mean disease duration of 11 years (sd7) and DAS28 of 3.5 (sd1.3) at baseline were followed during 1.5 years. Inter-individual variability in infliximab levels in patients with low DAS28 was high (median 1.4 mg/L, IQR 3.35), with 31% (95%CI: 20-42%) having low (<1 mg/L) and 14% (95%CI 5–22) high trough levels (>5 mg/L). Interestingly also in RA patients with DAS28 ≤ 3.2, anti-infliximab antibodies were found in one-third of the patients, with half of them having antibodies every visit during a median of more than one year. Agreement for consecutive measurements of serum trough levels and anti-infliximab antibodies was high in stable patients: r = 0.97 (p = 0.00001) and kappa = 1.0 (SE 0.14) Anti-infliximab antibody appearance was influenced by interval increases (relative risk (RR) 5.2, 2.6-10.7), but patients still showed low infliximab levels.ConclusionsLow (and high) infliximab serum trough levels are prevalent, interestingly also in patients with low disease activity. Consecutive measurements of serum trough levels and anti-infliximab antibodies are reliable in stable patients. These test could be used to lower or stop infliximab in selected patients.
Highlights
To get insight in the prevalence of high, or low/no serum infliximab trough levels in patients with low disease activity and if serum trough levels are stable and reliable longitudinally we conducted a prospective cohort study
Patient characteristics and infliximab serum trough levels In total 1320 visits in 147 patients treated with infliximab for at least 6 months were collected in the observation period
Low infliximab serum trough levels in patients with long term low disease activity Since at study enrolment a relatively high percentage of low infliximab serum trough level was found in patients with low disease activity, we examined whether the presence of low serum trough levels was persistent in patients with stable low disease activity
Summary
To get insight in the prevalence of high, or low/no serum infliximab trough levels in patients with low disease activity and if serum trough levels are stable and reliable longitudinally we conducted a prospective cohort study. In the maintenance phase of treatment with infliximab there are still large inter-individual differences in disease activity, as witnessed by the relatively high mean and large variation in disease activity scores (mean DAS28 in the DREAM registry after one year was about 4) and large proportion of patients with high disease activity in biological registries (for example about 45% in the NORDMARD database had a DAS28 > 3.2 after 6 months) [8,9] This can be explained by inadequate initial response, and by the occurrence of secondary loss of response after initial improvement on infliximab.
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