Background We previously used MMP3 and CDAI, composite measures that do not include acute-phase protein – that is, CRP/ESR – to study the results of 52 weeks of routine clinical treatment with tocilizumab (TCZ), and reported that CRP turned negative at 12 weeks and a decrease in MMP3 to a certain level or below at 24 weeks are predictors of CDAI low disease activity or remission at 52 weeks. Although it is important to continue drug therapy uninterrupted for the maintenance of low disease activity or remission, for financial reasons, the use of smaller quantities of expensive pharmaceuticals should be considered.

Objectives We prospectively investigated if extended drug interval would be possible once stable status in disease activity had been achieved in TCZ therapy.

Methods Of the 130 patients receiving TCZ therapy at our institution, we conducted this study in 20 patients who consented to extended drug interval. Four of the subjects were male and 16 were female. Their mean age was 55.9 years, their mean disease duration was 12.2 years, 19 of them were RF positive, 14 were bio-naive, and all were RA patients who were being treated with TCZ but without MTX. Their mean DAS28-ESR prior to extended interval dosing initiation was 2.3, and their mean CDAI was 7.7. The drug interval was intentionally extended to 5 weeks or longer (to between 5 weeks and 8 weeks), and the patients’ disease activity (CDAI and SDAI) and CRP levels, a measure of the TCZ blood concentration, were investigated. Patients were returned to a drug interval of 4 weeks when disease activity increased following drug interval extension, when the patients requested it, or when their CRP levels increased and the disappearing levels of TCZ in the blood became a concern.

Results At the final observation time point, 6 of the patients had been able to remain on extended drug interval and 14 had not and had needed to be returned to a 4-week interval. Comparison of the disease activity at extended interval initiation in these 2 groups revealed that the CDAI and SDAI were 2.7±0.7 and 2.9±0.7, respectively, in the former group and 9.8±6.0 and 10.1±6.0, respectively, in the latter group, differences that were significant (Wilcoxon signed-rank test).

In addition, although half of patients with CDAI ≤10 and CRP turned negative at extended interval initiation were able to remain on extended interval, all of the patients without CDAI ≤10 who had not turned negative needed to return to 4-week interval.

Conclusions Patients with CDAI ≤10 and CRP turned negative were able to remain on TCZ extended interval, but all other patients experienced a return of disease activity. The results of our study affirmed the importance of the maintenance of remission and CRP-negative status in RA patients receiving TCZ. We therefore concluded that, as a rule, TCZ 8 mg/kg should be administered in the maintenance phase, and a 4-week interval should continue to be used. However, our study had certain limitations – it was conducted in RA patients with a long disease duration who could not receive concomitant MTX because of prior or current adverse reactions – and extended interval dosing may have been possible if we had performed our study in early-stage, bio-naïve RA patients capable of receiving concomitant MTX.

1. Rheumatology International DOI: 10.1007/s00296-011-2256-5.

Disclosure of Interest None Declared