Due to emerging resistance, new antibiotic options are needed to treat CF acute pulmonary exacerbations caused by methicillin resistant Staphylococcus aureus (MRSA). There is established evidence that adult patients with cystic fibrosis (CF) may have altered antibiotic pharmacokinetics compared with non-CF patients. Telavancin is a lipoglycopeptide antibiotic that has activity against gram-positive bacteria including MRSA. This study will determine the pharmacokinetics and tolerability of telavancin in 18 adult CF patients admitted for a pulmonary exacerbation at 1 of 4 participating hospitals in the US.