Drug vignettes: Tocilizumab

May 1, 2020

Robin E Ferner*, Jeffrey K Aronson

On behalf of the Oxford COVID-19 Evidence Service Team
Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences
University of Oxford
*University of Birmingham

Correspondence to r.e.ferner@bham.ac.uk


Patients with severe COVID-19 can develop cytokine release syndrome (“cytokine storm”) and are reported to have high circulating IL-6 concentrations. Tocilizumab is a recombinant humanized anti-human IgG1 monoclonal antibody directed against the interleukin-6 receptor (IL-6R). It has therefore been proposed to be of value in the management of severe COVID-19.

Mechanism of action
Tocilizumab binds specifically to both soluble and membrane-bound interleukin-6 receptor (IL-6R) with a pKd of 8.6 (i.e. Kd = 2.5 nmol/L). It is a competitive inhibitor of IL-6-mediated signalling.

IL-6 is a cytokine involved in haemopoiesis, acute phase reactions, and immune responses, such as T-cell activation and induction of immunoglobulin secretion. It is produced by T- and B-lymphocytes, monocytes, fibroblasts, and other cells. Excessive production of IL-6 is implicated in, for example, multiple myeloma and rheumatoid arthritis.

In an animal model, tocilizumab suppressed the development of arthritis and the synthesis of C-reactive protein (CRP).

Circulating IL-6 concentrations are raised in patients with SARS and COVID-19. IL-6 activates a downstream Janus kinase (JAK) and excessive signalling leads to many effects that contribute to organ damage, such as maturing naïve T cells into effector T cells, inducing expression of vascular endothelial growth factor (VEGF) in epithelial cells, increasing vascular permeability, and reducing myocardial contractility.

Indications for licensed formulations
Tocilizumab is licensed in the UK and the USA, with some limitations, for the treatment of:

  1. severe, active, and progressive rheumatoid arthritis;
  2. active systemic juvenile idiopathic arthritis;
  3. juvenile idiopathic polyarthritis, in combination with methotrexate (MTX);
  4. giant cell arteritis (subcutaneous formulation)
  5. chimeric antigen receptor (CAR) T cell-induced severe or life-threatening cytokine release syndrome (CRS).

All of these indications are to treat chronic diseases, apart from the cytokine release syndrome, for which the FDA approved tocilizumab in 2017, on the basis of retrospective evidence of its effectiveness observed when it was used during prospective clinical trials of other interventions. It had previously been approved for the treatment of the chronic conditions listed above.Practical use in licensed indications
Tocilizumab is marketed in the UK by Roche Products Limited as RoActemra, in solutions containing 162 mg for injection (pens and syringes) and as a 20 mg/mL concentrate from which a solution for infusion can be prepared.

The effects of tocilizumab have been studied in several masked, controlled, randomized studies in rheumatoid arthritis. In a 52-week trial of nearly 800 patients, 20% of those treated with tocilizumab (8 mg/kg every four weeks) + methotrexate achieved a major clinical response (ARC 70), compared with 4% receiving placebo + methotrexate.

In a systematic review of 41 double-blind, randomized, controlled trials, non-controlled clinical trials, and open-label extensions lasting at least 6 months in patients with rheumatoid arthritis, tocilizumab monotherapy produced greater improvement than methotrexate monotherapy, as did the combination in patients who had failed to respond to methotrexate or anti-TNF therapy. However, the rate of serious infections was 4.7 events/100 patient-years of exposure in those who were given tocilizumab and there were also higher frequencies of neutropenia, thrombocytopenia, hyperlipidemia, and transaminase rises compared with placebo.

In rheumatic disease, tocilizumab is given by intravenous infusion once every four weeks, adjusted to the patient’s weight. The maximum recommended single dose is 800 mg. It can also be given by subcutaneous injection 162 mg once a week.

The dosage in the treatment of the cytokine release syndrome is a 60-minute intravenous infusion of 8 mg/kg in patients weighing 30 kg or more and 12 mg/kg in patients weighing less than 30 kg.

Pharmacokinetics
Tocilizumab has complicated pharmacokinetics. Its clearance depends on two pathways, one linear, one nonlinear. The nonlinear clearance is rapidly saturated at low concentrations, so that at high concentrations the linear clearance predominates and is about 10 mL/h, i.e. very low (compared with liver blood flow of 80 L/h). Thus, tocilizumab has a very long and dose-dependent half-life, increasing from 6 days at low concentrations to 18 days at high concentrations. The apparent volume of distribution is about 7 L. Mean steady-state trough serum concentrations (i.e. concentration at the end of a dosing interval) are about 45 mg/L at a weekly subcutaneous dose of 162 mg and 19 mg/L during 4-weekly intravenous administration.

Contraindications and warnings in licensed use
Serious and sometimes fatal infections have been reported. The manufacturer therefore recommends that treatment should not be started during an active severe infection, or with conditions that can predispose to infections (e.g. diverticular disease, diabetes mellitus, interstitial lung disease). It is not clear how these restrictions would affect its use in acute infection with SARS-CoV-2.

Tocilizumab can also cause reactivation of tuberculosis and hepatitis B virus infection.

Hypersensitivity to tocilizumab or any of the excipients in the formulations is a contraindication. This is a typical blanket warning that is included in Summaries of Product Characteristics. However, acute hypersensitivity reactions to tocilizumab are not uncommon with repeated administration (see below).

The manufacturers advise against starting treatment in patients with a neutrophil count below 2.0 × 109/L or a platelet count below 100 × 1012/L. They advise withholding treatment if the neutrophil count falls below 0.5 × 109/L or the platelet count below 50 × 1012/L. They also advise caution in starting treatment in patients with liver transaminase activities more than 1.5 times the upper limit of normal and withholding treatment if transaminase activity rises above 3–5 times the upper limit of normal.

Adverse effects
Very common adverse effects (more than 1 in 10 people affected) include:

      • Upper respiratory tract infections
      • Hypercholesterolaemia

Common adverse effects (between 1 in 10 and 1 in 100 people affected) include:

      • Herpes simplex, herpes zoster, cellulitis, pneumonia
      • Gastritis and mouth ulcers
      • Rashes
      • Raised transaminase activities, hyperbilirubinaemia
      • Hypertension
      • Leukopenia, neutropenia, hypofibrinogenaemia
      • Conjunctivitis
      • Cough and dyspnoea

Hypersensitivity reactions occur in about 1.5% of patients with rheumatoid arthritis.

Drug-drug interactions
During cytokine storm drug metabolism by CYP isoenzymes is suppressed. Thus, successful treatment with tocilizumab may return to normal the metabolism of other drugs, such as methylprednisolone and dexamethasone.

Experience with tocilizumab in cytokine release syndrome
Administration of chimeric antigen receptor T (CAR-T) cells can cause a cytokine release syndrome, which has been treated with tocilizumab. The appropriate timing of therapy has not been well described.

The IL-6 concentration in 69 patients correlated with concentrations of CRP, ferritin, and D-dimers. An improvement in the radiographic appearance was accompanied by reduction in IL-6 concentration. However, since IL-6 clearance is mediated by the IL-6 receptor, blocked by tocilizumab, IL-6 accumulates in the serum during tocilizumab treatment, so it may not be a good marker of disease activity in tocilizumab-treated patients.

Experience with tocilizumab in virus infections other than COVID-19
IL-6 generated in damaged lung tissue has been implicated in the inflammatory myopathy that can occur in influenza A, and tocilizumab attenuated influenza-induced muscle dysfunction in experiments in mice.

The authors of a Japanese study of the course of influenza A infection in ten patients with juvenile rheumatoid arthritis receiving tocilizumab treatment concluded that “IL-6 inhibition by tocilizumab reduced inflammation associated with infection and resulted in mild symptoms during influenza.” Eight of the ten patients also received oseltamivir or zanamivir.

Experience with tocilizumab in COVID-19
Typical protocols include:

      • 400 mg intravenously;
      • 8 mg/kg on day 1, repeated on day 3 if there is no response;
      • 8 mg/kg up to a maximum of 800 mg, repeated once if symptoms worsen or there is no response.

Cao noted a small, apparently uncontrolled, Chinese trial of tocilizumab in which 21 patients with severe disease, including two who were critically ill, recovered. No other clinical data were provided.

A French patient with metastatic renal cell cancer developed fever, tested positive for SARS-CoV-2, and was treated with lopinavir–ritonavir. His condition deteriorated suddenly on day 8 of his illness, he was given two intravenous doses of tocilizumab 8 mg/kg six hours apart, and his clinical state improved rapidly.

A Chinese group reported the effects of tocilizumab in 15 patients, of whom seven were said to be critically ill. Eight patients were treated with methylprednisolone in addition. “Although TCZ treatment ameliorated the increased CRP in all patients rapidly, for the 4 critically ill patients who received only single dose of TCZ, 3 of them (No. 1, 2, and 3) still dead [sic] and the CRP level in the rest 1 patient (No. 7) failed to return to normal range with a clinical outcome of disease aggravation.” The authors reasonably concluded that, while a single dose of tocilizumab in combination with methylprednisolone failed to reduce disease activity, there was some suggestion that repeated doses of tocilizumab were clinically beneficial.

The effects of tocilizumab in addition to routine therapy have been retrospectively analysed in 21 Chinese patients with severe or critical COVID-19. The authors of a non-peer-reviewed account of the results, subsequently published, reported that within a few days fever abated and all other symptoms improved; 15 patients needed less oxygen intake and one needed none at all; lung opacities in CT scans “were absorbed” in 19 patients. The peripheral lymphocyte counts, which were below normal in 17 of 20 patients before treatment, returned to normal in 10 out of 19 by 5 days, and abnormally high C-reactive protein concentrations fell significantly in 16 out of 19 patients. These are apparently encouraging results, but the study was small and retrospective and there was no control group for comparison. In different parts of the paper the authors refer to either 20 or 21 patients; in the tables, the demographic data refer to 21, but the laboratory data refer to anything from 12 to 20 patients or do not specify; the results of oxygen therapy are described in 20 patients. We have not found a prespecified protocol.

Outlook
Tocilizumab has been used to treat cytokine release syndrome due to CAR-T cell therapy. However, its use in COVID-19 is experimental. It should not be used except in the context of clinical trials to establish whether the benefits outweigh the harms of treatment.

Registered trials
We are currently (27 April) aware of 35 trials involving tocilizumab, either alone or in combination with other medications (registered in European and Chinese trials registries and clinicaltrials.gov). Of those, one is single-blind (investigator-blind) and four are double-blind. In all, 1590 participants are scheduled to be studied in the masked trials compared with 10,636 in the unmasked trials (15%).

Disclaimer: This article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the NHS, the NIHR, or the Department of Health and Social Care. The views are not a substitute for professional medical advice.