Background/Purpose: In the MUSASHI study (i.e., Double-blind, parallel-group, Phase III non-inferiority study comparing subcutaneous tocilizumab [SC-TCZ] monotherapy versus intravenous tocilizumab [IV-TCZ] monotherapy), the effectiveness and safety of SC-TCZ monotherapy were proved to be comparable to those of IV-TCZ monotherapy in Japanese patients with rheumatoid arthritis (RA). The aim of the current study was to investigate the effectiveness and safety of SC-TCZ in the patients who had received IV-TCZ in the MUSASHI study.

Methods: This study enrolled RA patients who had received TCZ monotherapy for 24 weeks in the MUSASHI study (prior-IV group: 8 mg/kg IV-TCZ every 4 weeks; prior-SC group: 162 mg SC-TCZ every 2 weeks). They received open label SC-TCZ (162 mg every 2 weeks) starting at Week 24 without any concomitant use of synthetic or biologic DMARDs. Disease activity as measured by DAS28-ESR and ACR response rates and safety were assessed.

Results: A total of 319 patients (160 patients in the prior-IV group and 159 patients in the prior-SC group) were enrolled. Baseline demographics were comparable between the prior-IV group and the prior-SC group: body weight (kg, mean ± SD), 54.3 ± 10.1 vs. 53.9 ± 8.8; proportion of patients who previously used TNF-α inhibitors before the MUSASHI study, 23.1% vs. 18.2%. At 12 weeks after starting the extension period (36 weeks after the beginning of the MUSASHI study), 158 patients in the prior-IV group and 157 patients in the prior-SC group were still receiving SC-TCZ. The mean change of DAS28-ESR in the prior-IV group was comparable to that in the prior-SC group over the whole 36 weeks, and was maintained after switching from IV-TCZ to SC-TCZ (Table). ACR response rates at Week 24 were also maintained for the 12 weeks following the switch from IV-TCZ to SC-TCZ. The incidences of new onset AEs and SAEs between Weeks 24 and 36 were, respectively, 59.4% (95/160) and 4.4% (7/160) in the prior-IV group and 57.9% (92/159) and 2.5% (4/159) in the prior-SC group. The safety profiles in both groups were comparable. Among AEs, the incidence of new onset injection-site reactions (ISRs) was 5.6% (9/160) in the prior-IV group. No case of serious ISR was seen during the extension period in the prior-IV group and the prior-SC group. Anti-TCZ antibodies were detected in 1 patient who switched from IV to SC administration. However this patient had no case of serious anaphylaxis or anaphylactoid reactions.

Conclusion: There was no sign of effectiveness being reduced after switching to SC-TCZ in this short extension period. Switching of TCZ treatment from IV-TCZ to SC-TCZ was tolerable. These findings are useful consideration for the clinical application of SC-TCZ.

Table: DAS28-ESR over time (mean ± SD)

	Double blind period			Extension period
week	0	12	24	36
Prior-SC*1	6.1 ± 0.9	3.1 ± 1.2	2.7 ± 1.3	2.6 ± 1.4
Prior-IV*2	6.2 ± 0.9	2.8 ± 1.0	2.5 ± 1.1	2.6 ± 1.2

^*1 Prior-SC: SC-TCZ 162 mg q2w

^*2 Prior-IV: IV-TCZ 8 mg/kg q4w for 24 weeks and then switched to SC-TCZ 162 mg q2w

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effectiveness-and-tolerability-of-subcutaneous-tocilizumab-in-rheumatoid-arthritis-patients-switched-from-intravenous-tocilizumab-results-from-the-extension-period-of-the-musashi-study/