But with its peptide-like structure, PF-00835231 is rich in hydrogen bond donors. It has five of them, and they give the molecule a polar surface area that traps it in the gut if swallowed. This means the molecule must be administered intravenously—something that can typically only be done in a hospital setting. Pfizer scientists wanted an antiviral pill that people could take at the first signs of infection, long before they had to go to the hospital.