The purpose of this study is to characterize the Pharmacokinetic and to confirm the popPK model derived from healthy volunteers in hospitalized adults who are infected with respiratory syncytial virus (RSV) and to determine in adults who are hospitalized with respiratory syncytial virus (RSV) infection the dose response relationship of multiple regimens of lumicitabine on antiviral activity based on nasal RSV shedding using quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) assay.