Introduction
============

Rheumatoid arthritis (RA) is a chronic, progressive, inflammatory disease associated with joint destruction.[@b1-dddt-8-913] The inflammation in RA is in part due to proinflammatory cytokines, such as tumor necrosis factor (TNF)-alpha.  Biological agents against these cytokines have dramatically changed the management of patients with RA.[@b2-dddt-8-913]--[@b5-dddt-8-913] The recent consensus is that patients with progressive joint destruction should be treated with biologics to achieve tight disease control and remission.  Recent studies showed that the concomitant administration of anti-TNF biologics and methotrexate led to remission in a significant percentage of patients.[@b6-dddt-8-913]--[@b8-dddt-8-913] Such biologics induce a rapid therapeutic response and now play an essential role in the treatment of RA; however, not all patients respond to existing biologics and must switch to other drugs.  Therefore, new drugs that target other molecules are needed. 

Interleukin-6 (IL-6) is an inflammatory cytokine that is abundantly expressed in the serum and inflamed synovial tissue of RA patients.[@b9-dddt-8-913]--[@b11-dddt-8-913] IL-6 acts on a wide range of cells that are strongly activated in RA, such as neutrophils, T-cells, B -cells, monocytes, and osteoclasts.  The IL-6 blockade was, therefore, considered a promising candidate for the treatment of RA.  Tocilizumab (TCZ) is a humanized monoclonal anti-IL-6 receptor (IL-6R) antibody that was developed to inhibit the action of IL-6.[@b12-dddt-8-913]--[@b14-dddt-8-913] TCZ blocks IL-6 signaling by binding to both soluble and membrane-bound IL-6R; it was initially developed for use as an intravenous infusion (TCZ-IV).  The efficacy and safety of TCZ-IV were previously demonstrated as monotherapy and in combination with disease-modifying antirheumatic drugs (DMARDs) in adult patients with RA.[@b15-dddt-8-913]--[@b28-dddt-8-913] Accumulated clinical data on TCZ-IV suggested that TCZ is an important treatment option in patients with moderate-to-severe RA as both an initial biologic and for use following the failed trials of other drugs. 

To achieve clinical, functional, and structural remission or the lowest disease activity state possible, each patient's disease status should be considered, along with the efficacy, safety, and route of administration of each therapy.  Some patients prefer subcutaneous (SC) injection of biologic agents rather than intravenous administration and may favor self-administration.[@b29-dddt-8-913]--[@b31-dddt-8-913] An SC formulation of TCZ (TCZ-SC) would provide an additional treatment option for patients with RA.  A TCZ-SC dose of 162 mg every 2 weeks (q2w) or weekly (qw) was selected based on pharmacokinetic and pharmacodynamic studies and was approved in 2013.[@b32-dddt-8-913]--[@b34-dddt-8-913] At present, only limited data on the efficacy and safety of TCZ-SC are available.  This article reviews the use of TCZ-SC in adult patients with active RA. 

Pharmacokinetic and pharmacodynamic properties of TCZ-SC
========================================================

This section discusses the pharmacokinetic and pharmacodynamic properties of TCZ-SC, focusing on the data from the MATSURI study, a report by Zhang et al, and the SUMMACTA study.[@b33-dddt-8-913]--[@b35-dddt-8-913] The details are shown in [Table 1](#t1-dddt-8-913){ref-type="table"}.  We must take into consideration the differences in the subjects' body weights and the evaluation periods in each study.  Ohta et al (MATSURI study) reported that 3 weeks after a single SC administration of TCZ, the area under the serum TCZ concentration (AUC) values following 81 mg and 162 mg doses were 513.6 μgh/mL and 2,320.8 μgh/mL, and the maximum TCZ concentration (C~max~) values were 3.4 μg/mL and 10.9 μg/mL, respectively, demonstrating the nonlinear pharmacokinetics of TCZ-SC.[@b34-dddt-8-913] The serum trough TCZ concentration was under the detectable level until the dosing frequency was increased to qw at week 9 in the 81 mg q2w group.  In contrast, the mean serum trough TCZ concentrations of ≥1 μg/mL were maintained in 88% of 162 mg q2w patients and 100% of 162 mg qw patients.  Both doses had exposures comparable to the approved TCZ-IV dose of 8 mg/kg.  Although the C-reactive protein (CRP) normalization rate increased over time, not all patients in the 81 mg q2w group achieved normalized CRP levels.  In contrast, all patients in the 162 mg q2w group achieved normalized CRP levels by week 7, which were subsequently maintained.  All patients in the 162 mg qw group achieved normalized CRP levels by week 3.  The study authors concluded that the appropriate TCZ-SC dose was 162 mg q2w for Japanese patients whose mean body weight was about 53 kg. 

Zhang et al compared TCZ-SC doses of 162 mg SC qw and q2w at 12 weeks after initiation in patients with RA whose mean body weight was about 80 kg.[@b33-dddt-8-913] After final dosing, TCZ-SC qw and q2w were associated with AUC values of 5,505 μgh/mL and 2,332 μgh/mL, and C~max~ values of 39.4 μg/mL and 10.7 μg/mL, respectively.  The median CRP levels decreased in both groups after the first dose of TCZ-SC.  Normal CRP levels were achieved after single administration in the qw group.  In the q2w group, median CRP levels fluctuated after the first three doses, with the elevations occurring between the dosing weeks.  However, normal CRP levels were achieved consistently after three doses.  They concluded that both TCZ-SC regimens demonstrated clinical benefit, although greater soluble IL-6R levels and more rapid normalization of CRP levels were observed with the qw regimen than the q2w regimen.  It is suggested that TCZ-SC qw could be considered in patients with greater body weight. 

Burmester et al (SUMMACTA study) found that at 20--24 weeks following the administration of TCZ-SC 162 mg qw and TCZ-IV 8 mg/kg q4w, the AUC values were 30,168 μgh/mL and 41,304 μgh/mL, and the C~max~ values were 52.7 μg/mL and 223 μg/mL, respectively.[@b35-dddt-8-913] The CRP levels decreased in both groups after the first dose of TCZ and, subsequently, remained below the upper limit of normal until week 24.  The time course of CRP levels for TCZ-SC was comparable to that for TCZ-IV. 

Summary
-------

Based on the MATSURI study, it is clear that TCZ-SC 81 mg q2w does not reach sufficient concentrations to result in clinical efficacy even in Japanese patients whose mean body weight was thought to be small.  Two other studies[@b33-dddt-8-913],[@b35-dddt-8-913] showed that both TCZ-SC 162 mg q2w and qw showed equivalent effects to TCZ-IV in most patients; however, TCZ-SC 162 mg qw regimens consistently showed more rapid effects in terms of CRP normalization. 

Efficacy
========

At present, five studies have reported the efficacy of TCZ-SC in patients with RA.  They are: a report by Zhang et al;[@b33-dddt-8-913] the MATSURI study (2013); the BREVACTA study (2013); the MUSASHI study (2014); and the SUMMACTA study (2014).[@b33-dddt-8-913]--[@b37-dddt-8-913] The first two were open-label studies to determine TCZ-SC doses in small numbers of patients.  The last three were large (n\>100), randomized, controlled, and multicenter studies of up to 24 weeks' duration, using doses of 162 mg q2w or qw.  The TCZ-SC efficacy findings obtained in these studies are summarized in [Table 2](#t2-dddt-8-913){ref-type="table"}.  Importantly, there were differences in the doses of TCZ-SC and concomitant DMARDs used in each study.  For TCZ-SC, the dose was 162 mg q2w in the BREVACTA and the MUSASHI studies; in the SUMMACTA study, it was 162 mg qw. 

The MATSURI study was designed as a multicenter, open-label, dose-escalation study to determine the optimal TCZ-SC dose that would result in exposure comparable to the approved 8 mg/kg TCZ-IV dose in patients with RA.[@b34-dddt-8-913] No concomitant conventional DMARDs were allowed in this study.  Patients received TCZ-SC at 81 mg q2w, 162 mg q2w, or 162 mg qw for 25 weeks.  As described previously, the CRP normalization rate (patients achieving levels \<1 mg/dL) was 2/8 patients (25%) at 3 weeks in the 81 mg q2w group.  In contrast, all of the patients in the 162 mg q2w and qw groups achieved normalized CRP levels by week 7 and subsequently maintained normal levels.  In the 81 mg q2w group, the American College of Rheumatology (ACR) 20 response rate was 13% (one of eight patients) through week 9.  No patients in this group achieved an ACR 50 response.  After the dosing frequency was increased to qw at week 9 in the 81 mg q2w group, the ACR 20 and ACR 50 response rates increased and reached 38% (three of eight patients).  The ACR 20 and ACR 50 response rates did not differ significantly between the 162 mg q2w and 162 mg qw groups after week 7.  The ACR 20 response rate increased to 83% (ten of 12 patients) at week 13 in both groups.  The ACR 50 response rate increased to 75% (nine of 12 patients) by week 17 in the 162 mg qw group and to 83% (ten of 12 patients) by week 21 in the 162 mg q2w group; they remained at this level until the last observation.  The ACR 20, ACR 50, and ACR 70 response rates as well as the disease activity score (DAS) 28 remission (DAS 28\<2.6) rate at week 25 were not significant between the 162 mg q2w and 162 mg qw groups; however, the 162 mg qw group constantly showed the slightly better results. 

The MUSASHI study was designed as a double-blind, parallel-group, double-dummy, comparative Phase III study for Japanese patients.[@b36-dddt-8-913] No concomitant conventional DMARDs were allowed.  The primary endpoint was the noninferiority of TCZ-SC to TCZ-IV as determined by ACR 20 response rates.  Patients were randomized to receive TCZ-SC 162 mg q2w or TCZ-IV 8 mg/kg q4w.  At week 24, ACR 20 response was achieved in 79.2% of the TCZ-SC group and in 88.5% of the TCZ-IV group.  DAS 28 remission at week 24 was 49.7% in the TCZ-SC group and 62.2% in the TCZ-IV group.  ACR 50 and ACR 70 response rates at week 24 were also similar between the groups.  The authors concluded that TCZ-SC monotherapy 162 mg q2w demonstrated comparable efficacy to TCZ-IV monotherapy.  However, logistic regression analyses showed that baseline body mass index in the fourth quartile (23.4--29.6 kg/m^2^) was associated with a significantly lower ACR 20 response rate (63.4%; odds ratio \[OR\] 0.31; *P*=0.0048), ACR 50 response rate (51.2%; OR 0.47; *P*=0.0444), and ACR 70 response rate (24.4%; OR 0.39; *P*=0.0271).  This result was not unexpected since TCZ-SC monotherapy was administered as a fixed dose (162 mg); whereas, the TCZ-IV monotherapy formulation was dosed by body weight (8 mg/kg).  Although no significant differences in efficacy were observed between the two groups, TCZ-IV consistently showed slightly better results.  These trends might indicate lower efficacy in patients with greater body weight.  The BREVACTA study also showed that treatment with TCZ-SC 162 mg q2w plus concomitant DMARDs was clinically effective, resulting in ACR 20, 50, and 70 response rates of 61%, 40%, and 20%, respectively.[@b37-dddt-8-913]

In contrast, therapy with TCZ-SC 162 mg qw and concomitant DMARDs was assessed in the SUMMACTA study, a randomized, double-blind, parallel-group study of TCZ-SC versus TCZ-IV in patients with moderate to severe RA.[@b35-dddt-8-913] Patients (n=1,262) were randomly assigned to receive TCZ-SC 162 mg qw or TCZ-IV 8 mg/kg q4w in combination with conventional DMARDs.  The primary outcome was the noninferiority of TCZ-SC to TCZ-IV with regard to the proportion of patients achieving an ACR 20 response at week 24.  At week 24, 69.4% of the TCZ-SC group versus 73.4% of the TCZ-IV group achieved an ACR 20 response.  ACR 50/70 responses, DAS 28, and physical function improvements were comparable between the two groups.  The authors concluded that TCZ-SC 162 mg qw was noninferior to TCZ-IV 8 mg/kg q4w. 

Summary
-------

Based on the MATSURI study, it could be concluded that the TCZ-SC 81 mg q2w regimen was not sufficient for clinical efficacy.  Both TCZ-SC 162 mg q2w and qw were not inferior to TCZ-IV 8 mg/kg q4w; however, the MUSASHI study revealed that the greater body mass index resulted in the lower ACR 20 response rate.  In contrast, TCZ-SC 162 mg qw seemed to have the equivalent efficacy with the TCZ-IV 8 mg/kg q4w. 

Safety
======

TCZ-SC qw or q2w was generally well-tolerated when administered as monotherapy or in combination with DMARDs for up to 24 weeks ([Table 3](#t3-dddt-8-913){ref-type="table"}).  The rates of withdrawal due to adverse events were generally low: 4.8% in the BREVACTA study; 1.7% in the MUSASHI study; and 4.8% in the SUMMACTA study.[@b35-dddt-8-913]--[@b37-dddt-8-913] These were comparable to or slightly better than the rates in the groups treated with TCZ-IV 8 mg/kg.  The wide variety of adverse events reported falls into several basic categories: infection; lipid level; liver enzyme; hematological parameters; and injection site reactions (ISR).  Incidences of adverse events are summarized in [Table 3](#t3-dddt-8-913){ref-type="table"}. 

Infection
---------

The incidence of serious infections associated with TCZ-SC was generally low and was comparable with TCZ-IV.  The MUSASHI study reported two serious infections (1.2%), cellulitis, and gastroenteritis.[@b36-dddt-8-913] In the SUMMACTA study, serious pneumonia occurred in two patients in each group and bacterial arthritis occurred in two patients in the TCZ-IV group.[@b35-dddt-8-913] The most common reason for withdrawal due to adverse events in both groups was infection (1.1% TCZ-SC and 1.3% TCZ-IV).  No obvious difference in the incidence of serious infections was observed between the treatment groups. 

Lipid levels
------------

Moderate increases in serum total cholesterol and triglyceride had been reported in the treatment of TCZ-IV.[@b15-dddt-8-913] TCZ-SC treatment also showed the variable value of elevated total cholesterol.  The MUSASHI study showed 18.5% of the patients with the shift in total cholesterol from baseline \<200 mg/dL to \>240 mg/dL; whereas, in the SUMMACTA study, that number was 7.0%.  The proportion of patients with an increase in total cholesterol was slightly higher in the TCZ-SC group than in the TCZ-IV group in the SUMMACTA study; however, this trend was not noted in the MUSASHI study.[@b36-dddt-8-913] No patients withdrew from the study due to elevated total cholesterol or triglycerides. 

Liver enzymes
-------------

The mild-to-moderate elevation of hepatic transaminases, which were not associated with hepatic injury, has been commonly reported in patients receiving TCZ-IV.[@b15-dddt-8-913] More than 20% of patients receiving TCZ-SC experienced elevations of alanine aminotransferase and aspartate aminotransferase from normal at baseline to \< three times the upper limit of normal, while 1%--5% showed elevations to \> three times this level.  No patients withdrew from the MUSASHI study due to liver dysfunction.[@b36-dddt-8-913] In the SUMMACTA study, five patients (0.8%) in the TCZ-SC group and seven patients (1.1%) in the TCZ-IV group withdrew due to elevated liver transaminases.[@b35-dddt-8-913]

Hematological parameters
------------------------

Treatment with TCZ-IV was associated with the transient decrease of neutrophils.[@b15-dddt-8-913] In the MUSASHI group, the proportion of patients who experienced a decrease in neutrophils (\<1,000--500 cells/mm^3^) was 2.9% (five of 173 patients) in both the TCZ-SC and TCZ-IV groups; one patient in the TCZ-SC group withdrew from the study for this reason.[@b36-dddt-8-913] No grade 4 neutropenia (\<500 cells/mm^3^) was reported.  In the SUMMACTA study, about 3% of the patients showed a decrease in neutrophils to \<1,000--500 cells/mm^3^. No differences were observed between the groups.[@b35-dddt-8-913] One patient in the TCZ-SC group experienced a sustained consecutive neutrophil decline. 

ISR
---

The ISR site reaction in BREVACTA study,[@b37-dddt-8-913] MUSASHI study,[@b36-dddt-8-913] and SUMMACTA study[@b35-dddt-8-913] was 10.3%, 12.1%, and 10.1%, respectively.  The incidence of ISR was more compared to patients with placebo in both the MUSASHI and SUMMACTA studies.  Among the reported ISR, the common events were injection site erythema, injection site hemorrhage, pruritus, swelling, and pain.  All the ISRs were mild, and no cases withdrew from the studies due to the ISR. 

Summary
-------

The rate of withdrawal from TCZ therapy due to adverse events was generally low in all studies, and similar profiles were observed in the TCZ-SC and TCZ-IV groups.  TCZ-SC qw or q2w was generally well-tolerated when administered as monotherapy or in combination with DMARDs for up to 24 weeks.  ISRs thought to be specific to the SC formulation were seen in approximately 10% of patients. 

Conclusion
==========

TCZ-SC monotherapy or in combination with DMARDs demonstrated comparable efficacy and safety to TCZ-IV in patients with active RA who previously had an inadequate response to conventional DMARDs or biologics.  A SC formulation of TCZ would provide an additional treatment option for patients with RA and could save time and reduce the frequency of hospital visits.  Determining the optimal TCZ-SC dose requires further comparative investigation. 

This work was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (number 24592268). 

**Disclosure**

The authors report no conflicts of interest in this work. 

###### 

Pharmacokinetic and pharmacodynamic properties of TCZ-SC and TCZ-IV

                   MATSURI study[@b34-dddt-8-913]   Zhang et al[@b33-dddt-8-913]   SUMMACTA study[@b35-dddt-8-913]                             
  ---------------- -------------------------------- ------------------------------ --------------------------------- ------------- ----------- ---------
  AUC (μgh/mL)     513±799                          2,320±1,288                    5,505±2,632                       2,332±1,696   30,168      41,304
  C~max~ (μg/mL)   3.4±4.3                          10.9±5.6                       39.4±18.1                         10.7±6.57     52.7±27.3   223±117
  t~max~ (days)    1.5--6.0                         2.0--7.2                       2                                 3             NA          NA
  t~1/2~ (days)    NA                               1.6±0.24                       8±3                               3.5±2.21      NA          NA

**Notes:** Copyright © 2013.  Adapted from Zhang et al.  Pharmacokinetics and pharmacodynamics of tocilizumab after subcutaneous administration in patients with rheumatoid arthritis. * Int J Clinl Pharmacol Ther*.  2013;51(8):620--630, with the permission of Dustri-Verlag Dr Karl Feistle GmbH & Co. KG.[@b33-dddt-8-913] Data from MATSURI study,[@b34-dddt-8-913] and SUMMACTA study.[@b35-dddt-8-913] All the values are expressed as mean ± standard deviation. 

**Abbreviations:** TCZ, tocilizumab; SC, subcutaneous; IV, intravenous; q2w, every 2 weeks; qw, every week; q4w, every 4 weeks; AUC, area under the serum TCZ concentration; C~max~, maximum TCZ concentration; t~1/2~, half-life; NA, not available; t~max~, time to maximum concentration. 

###### 

Efficacy of TCZ-SC and TCZ-IV in patients with active RA

  Study                       Mean duration of RA (years)   Previous failed TNF-i therapy   \# of patients   Study duration (weeks)   TCZ treatment                                             Combined DMARDs   ACR 20 (%)   ACR 50 (%)   ACR 70 (%)   DAS remission rate (%)
  --------------------------- ----------------------------- ------------------------------- ---------------- ------------------------ --------------------------------------------------------- ----------------- ------------ ------------ ------------ ------------------------
  MATSURI[@b34-dddt-8-913]    7.8                           18.75%                          32               25                       SC 81 mg q2w[\*](#tfn4-dddt-8-913){ref-type="table-fn"}   No (mono)         38           38           38           50
                                                                                                             SC 162 mg q2w                                                                      83                83           50           83           
                                                                                                             SC 162 mg qw                                                                       92                92           67           100          
  BREVACTA[@b37-dddt-8-913]   NA                            21%                             437              24                       SC 162 mg q2w                                             Yes               61           40           20           NA
                                                                                                             Placebo                                                                            NA                NA           NA           NA           
  MUSASHI[@b36-dddt-8-913]    7.6                           21.2%                           348              24                       SC 162 mg q2w                                             No (mono)         79.2         63.5         37.1         49.7
                                                                                                             IV 8 mg/kg q4w                                                                     88.5              67.3         41.0         62.2         
  SUMMACTA[@b35-dddt-8-913]   8.7                           21%                             1,262            24                       SC 162 mg qw                                              Yes               69           47           24           38
                                                                                                             IV 8 mg/kg q4w                                                                     73                49           28           36           

**Notes:** Data are from a report by the MATSURI study,[@b34-dddt-8-913] the BREVACTA study,[@b37-dddt-8-913] the MUSASHI study,[@b36-dddt-8-913] and the SUMMACTA study.[@b35-dddt-8-913]

Dosing frequency was increased to qw at week 9 in the 81 mg q2w group. 

**Abbreviations:** RA, rheumatoid arthritis; TCZ, tocilizumab; SC, subcutaneous; IV, intravenous; TNF, tumor necrosis factor; TNF-i, TNF inhibitor; DMARDs, disease-modifying antirheumatic drugs; ACR, American College of Rheumatology; DAS, disease activity score; DAS remission, DAS \<2.6; mono, TCZ monotherapy; q2w, every 2 weeks; qw, every week; q4w, every 4 weeks; NA, not available. 

###### 

Incidence of adverse events receiving TCZ-SC and TCZ-IV

                                                                        BREVACTA study[@b37-dddt-8-913]   MUSASHI study[@b36-dddt-8-913]   SUMMACTA study[@b35-dddt-8-913]                
  --------------------------------------------------------------------- --------------------------------- -------------------------------- --------------------------------- ------------ ---------------------
  Discontinuation rate due to AEs                                       21 (4.8%)                         3 (1.7%)                         9 (5.2%)                          30 (4.8%)    42 (6.7%)
  Serious AEs                                                           25 (5.7%)                         13 (7.5%)                        10 (5.8%)                         34 (5.4%)    43 (6.8%)
  Serious infection                                                     12 (2.7%)                         2 (1.2%)                         5 (2.9%)                          9 (1.4%)     9 (1.4%)
  Shift in total cholesterol from baseline \<200 mg/dL to \>240 mg/dL   NA                                32 (18.5%)                       35 (20.2%)                        44 (7.0%)    26 (4.1%)
  Shift in ALT normal at baseline to value \>3× ULN                     NA                                5 (2.9%)                         9 (5.2%)                          30 (4.8%)    32 (5.1%)
  Shift in AST normal at baseline to value \>3× ULN                     NA                                2 (1.2%)                         6 (3.5%)                          6 (1.0%)     8 (1.3%)
  Shift in neutrophil normal at baseline to value \<1,000/mm^3^         NA                                5 (2.9%)                         5 (2.9%)                          18 (2.9%)    20 (3.2%)
  ISR                                                                   57 (10.3%)                        21 (12.1%)                       9 (5.2%) (placebo)                61 (10.1%)   15 (2.4%) (placebo)

**Notes:** Data are from a report by BREVACTA study,[@b37-dddt-8-913] MUSASHI study.[@b36-dddt-8-913] All values are expressed as number of the patients (%).  Data adapted from Burmester GR, Rubbert-Roth A, Cantagrel A, et al.  A randomised, double-blind, parallel-group study of the safety and efficacy of subcutaneous tocilizumab versus intravenous tocilizumab in combination with traditional disease-modifying antirheumatic drugs in patients with moderate to severe rheumatoid arthritis (SUMMACTA study). * Ann Rheum Dis*.  2014;73(1):69--74.[@b35-dddt-8-913] Copyright © 2014, BMJ Publishing Group Ltd and the European League Against Rheumatism. 

**Abbreviations:** TCZ, tocilizumab; SC, subcutaneous; IV, intravenous; AE, adverse events; ALT, alanine aminotransferase; AST, aspartate aminotransferase; ULN, upper limit of normal; ISR, injection site reaction; q2w, every 2 weeks; qw, every week; q4w, every 4 weeks; NA, not available.