BOSTON — Smoking appears to increase the likelihood of developing neutralizing antibodies to natalizumab (Tysabri, Biogen Idec), which cause the drug to have little, if any, therapeutic effect in multiple sclerosis (MS), a new study suggests.

The study was presented by Tomas Olsson, MD, Karolinska Hospital, Stockholm, Sweden, at the recent MS Boston 2014, the 2014 Joint Americas and European Committees for Treatment and Research in Multiple Sclerosis (ACTRIMS/ECTRIMS) meeting.

"The lung seems to be an important immunoreactive organ where irritation such as smoking may increase risk not only for inflammatory diseases, but also neutralizing antibodies to biologicals like interferon β and monoclonal antibodies such as natalizumab," he concluded.

"While smoking should not prohibit use of natalizumab, the percentage of patients developing antibodies, neutralizing the effect of the treatment, is not negligible," Dr Olsson commented to Medscape Medical News. "Therefore patients should be advised about our findings. This comes on top of an increased risk for MS with smoking, and probably a worse disease course."

In his presentation, Dr Olsson explained that smoking is thought to contribute to the induction of neutralizing antibodies to interferon β-1a, so he and his colleagues aimed to investigate the influence of smoking on the risk of developing antibodies to natalizumab, another biological drug in the treatment of MS.

The study was based on 1338 natalizumab-treated patients with MS included in either of two Swedish case-control studies in which information on smoking habits was collected. Treatment-related information was obtained from the Swedish national MS registry and antibody status from the Swedish Nab lab. Enzyme-linked immunosorbent assay was applied before therapy start and after 6, 12 and 24 months. Through use of logistic regression, patients with different smoking habits were compared regarding risk of developing anti-natalizumab antibodies.

Results showed that compared with nonsmokers, the odds ratio (OR) of developing anti-natalizumab antibodies was 2.4 (95% confidence interval [CI], 1.2 - 4.4) for patients who smoked at the time of screening, and a significant trend showed higher risk of developing antibodies with higher intensity of smoking.

The increased risk remained when smoking within 2 years prior to screening was considered (OR, 2.7; 95% CI, 1.5 - 5.1).

Still Try Natalizumab in Smokers

Commenting on the study for Medscape Medical News, Heinz Wiendl, MD, University of Münster, Germany, called this an "interesting observation," but he said the findings would not discourage him from using natalizumab in smokers.

"The prevalence of neutralizing antibodies to natalizumab is quite low — maybe affecting around 5% to 9% of patients. We can easily identify the patients who develop these antibodies because they don't respond to the drug."

He continued: "If a patient has neutralizing antibodies the drug effect will be zero. Natalizumab is a strong drug and there should be an obvious reduction of relapses and MRI lesions when a patient starts on it. If this does not happen, I think we can assume there are neutralizing antibodies present and then we would switch to a differemt treatment."

Dr Olsson has received nonrestricted MS research grants and/or compensations for lectures and advisory boards from Biogen Idec, Genzyme, Novartis, TEVA, and Merck. Dr Wiendl reports honoraria and consultation fees from Bayer HealthCare, Biogen Idec, Fresenius Medical Care, GlaxoSmithKline, GW Pharmaceuticals, Merck Serono, Novartis, Sanofi-Genzyme BioVentures, and Teva Pharmaceutical Industries.

MS Boston 2014: 2014 Joint Americas and European Committees for Treatment and Research in Multiple Sclerosis (ACTRIMS/ECTRIMS). Abstract PS5.4. Presented September 11, 2014.

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