EC50: 4.5 μM (RSV)

RD3-0028 has a 50% effective concentration of 4.5 μM and a 50% cytotoxic concentration of 271.0μM which is superior to that of ribavirin. RD3-0028 inhibits different RSV strains at a low concentration (4.5-11.0 μM) using the MTT method. Using the MTT method, EC ₅₀ values of RD3-0028 against tested strains are lower than those of ribavirin. RD3-0028 does not inhibit the replication of measles virus, influenza A virus, herpes simplex virus types 1 and 2, or human cytomegalovirus.

Aerosols generated from reservoirs containing RD3-0028 (7 mg/mL) administered for 2 h twice daily for 3 days significantly reduces the pulmonary titer of RSV-infected mice. It is clear that the minimal effective dose of RD3-0028 for RSV-infected mice is significantly less than that of ribavirin, the only compound currently available for use against RSV disease. Furthermore, the RD3-0028 aerosol administration protect the lungs of infected, CYP-treated mice against tissue damage, as evidenced by the preservation of the lung architecture and a reduction in pulmonary inflammatory infiltrates. RD3-0028 aerosol is not toxic for mice at the therapeutic dose. The plasma concentration of RD3-0028 is maintained at the same level from 5 min to 1 h, and decreases with a half-life of 2.2 h for 1±8 h. The excretion of radioactivity in the urine and faeces at 24 h after aerosol treatment is 89.3 and 4.5%, respectively, indicating that almost all the radioactivity is rapidly excreted in the urine. The excretion of total radioactivity is 98.9% within 168 h.