Mumbai: French drugmaker Sanofi and Regeneron of the US halted their clinical trials of rheumatoid arthritis drug Sarilumab after finding it did not improve the conditions of severely ill Covid-19 patients.The decision casts a shadow on other similar classes of drugs such as Tocilizumab by Swiss drug maker Roche pharma, that are under trial for treating Covid-19 in countries including India. However, the investigator leading the Tocilizumab trial in India told ET that the efficacy of these drugs on moderate Covid-19 patients still needs to be studied. In India, there is a multi-centre, randomised, controlled study to evaluate the clinical outcome and safety of Tocilizumab with 180 participants.The trials for this class of drug for Covid-19 started after some patients in China who were administered drugs such as Tocilizumab showed improvement in their oxygen levels and were discharged from hospital.This class of drugs is called interleukin-6 (IL-6) receptor blockers. IL-6 is a protein that mounts an immune response to infections. Some Covid-19 patients have high levels of IL-6, resulting in inflammation of the lungs and subsequently death, a process that’s come to be known as “cytokine storm.”According to Arvinder Singh Soin, who leads the Tocilizumab trial in India, the use of these drugs during advanced cytokine release syndrome when the patient is already on ventilator may be too late due to advanced lung damage and multi-organ dysfunction. While Sarilumab and Tocilizumab are similar, their affinity/effectiveness and potency in binding to the IL-6 receptor differ and so the results of one can’t be extrapolated to the other, Soin said.“We still have to see if Tocilizumab is different from Sarilumab and how effective it is against the receptor, whether the drugs work when the cytokine syndrome is not in advanced stage,” said Soin, adding that the result of the Sarilumab trial in the US is precisely why it’s important to prove or disprove effectiveness through randomised trials.During the trials in the US, adverse events were experienced by 80% of Kevzara patients and 77% of placebo patients, Sanofi said in a statement. A serious adverse event that occurred in at least 3% of the patients and more frequently among Kevzara patients was multi-organ dysfunction syndrome.“Based on the results, the US-based trial has been stopped, including in a second cohort of patients who received a higher dose of Kevzara (800 mg),” the companies said in the statement.In India, several doctors are using Tocilizumab off-label to treat Covid-19 patients, leading to a shortage of the drug and an increase in prices. One vial of the drug costs Rs 60,000 in India.Soin said excessive off-label use of Remdesivir, Tocilizumab and plasma therapy are getting in the way of trials in India and elsewhere.Roche is testing this drug in combination with another antiviral drug Remdesivir for moderate to severe Covid-19 patients.