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Rennard, Stephen I., Peter MA Calverley, Udo M. Goehring, Dirk Bredenbröker, a Fernando J. Martinez. Reduction of Exacerbations By the PDE4 Inhibitor Roflumilast - the Importance of Defining Different Subsets of Patients With COPD. BioMed Central, 2011.

Rennard, Stephen I., et al. Reduction of Exacerbations By the PDE4 Inhibitor Roflumilast - the Importance of Defining Different Subsets of Patients With COPD. BioMed Central, 2011.