Maike H M Wientjes1,2, Titia M G Gijzen1, Nathan den Broeder1, Karien Bloem3, Annick de Vries2, Bart J F van den Bemt4,5, Alfons A den Broeder1,6, Lise M Verhoef1. 1. Department of Rheumatology, Sint Maartenskliniek. 2. Radboud Institute for Health Sciences, Radboud University Medical Centre, Nijmegen. 3. Biologics Lab, Sanquin Diagnostic Services, Amsterdam. 4. Department of Pharmacy, Sint Maartenskliniek. 5. Department of Pharmacy, Radboud University Medical Centre. 6. Department of Rheumatology, Radboud University Medical Centre, Nijmegen, the Netherlands.
Abstract
OBJECTIVES: The REDO trial (REtreatment with Rituximab in RhEumatoid arthritis: Disease Outcome after Dose Optimisation) showed that ultra-low-dose rituximab (500 mg or 200 mg) was similarly effective to a 1000 mg dosage in the majority of RA patients. This pre-planned secondary analysis investigated (1) associations between rituximab dosage, drug levels, anti-drug antibodies (ADAs) and B-cell counts and (2) the predictive value of pharmacokinetic and pharmacodynamic parameters, and of patient, disease and treatment characteristics in relation to response to ultra-low-dose rituximab. METHODS: For 140 RA patients from the REDO trial, differences in drug levels, ADAs and B-cell counts were examined at baseline, and at 3 and 6 months after dosing. Treatment response was defined as absence of flare and no extra rituximab or >1 glucocorticoid injection received during follow-up. The association between potential predictors and response was investigated using logistic regression analyses. RESULTS: Lower doses of rituximab resulted in lower drug levels but did not significantly affect ADA levels or B-cell counts, and 3 (10.7%), 12 (20.7%) and 7 (13.0%) patients failed to meet the response criteria in, respectively, the 1000 mg, 500 mg and 200 mg dosage groups. Drug levels, ADAs, B-cell counts, and patient, disease and treatment characteristics were not predictive for response to ultra-low-dose rituximab. CONCLUSION: The results of this study further support the hypothesis that continued treatment with 500 or 200 mg rituximab is similarly effective to a 1000 mg dosage in RA patients doing well on rituximab. These results, combined with lack of finding a clinical dose-response relationship in the original REDO study, suggest that 200 mg rituximab is not yet the lowest effective rituximab retreatment dose in RA.
OBJECTIVES: The REDO trial (REtreatment with Rituximab in RhEumatoid arthritis: Disease Outcome after Dose Optimisation) showed that ultra-low-dose rituximab (500 mg or 200 mg) was similarly effective to a 1000 mg dosage in the majority of RA patients. This pre-planned secondary analysis investigated (1) associations between rituximab dosage, drug levels, anti-drug antibodies (ADAs) and B-cell counts and (2) the predictive value of pharmacokinetic and pharmacodynamic parameters, and of patient, disease and treatment characteristics in relation to response to ultra-low-dose rituximab. METHODS: For 140 RA patients from the REDO trial, differences in drug levels, ADAs and B-cell counts were examined at baseline, and at 3 and 6 months after dosing. Treatment response was defined as absence of flare and no extra rituximab or >1 glucocorticoid injection received during follow-up. The association between potential predictors and response was investigated using logistic regression analyses. RESULTS: Lower doses of rituximab resulted in lower drug levels but did not significantly affect ADA levels or B-cell counts, and 3 (10.7%), 12 (20.7%) and 7 (13.0%) patients failed to meet the response criteria in, respectively, the 1000 mg, 500 mg and 200 mg dosage groups. Drug levels, ADAs, B-cell counts, and patient, disease and treatment characteristics were not predictive for response to ultra-low-dose rituximab. CONCLUSION: The results of this study further support the hypothesis that continued treatment with 500 or 200 mg rituximab is similarly effective to a 1000 mg dosage in RA patients doing well on rituximab. These results, combined with lack of finding a clinical dose-response relationship in the original REDO study, suggest that 200 mg rituximab is not yet the lowest effective rituximab retreatment dose in RA.