SP-303 Small-particle aerosol treatment of influenza a virus infection in mice and respiratory syncytial virus infection in cotton rats

A natural plant product, SP-303, was administered by small-particle aerosol to influenza A/HK virus-infected mice and RSV-infected cotton rats. Aqueous SP-303 at 2 mg/ml in the Collison nebulizer reservoir generated an aerosol with an output of 26 μg/l and a particle size distribution of 1.4 μm ± 4.6 (MMAD±GSD). SP-303 at a dosage of 0.5–9.4 mg/kg per day administered for 3–4 days significantly increased both the rate and duration of survival of mice lethally infected with influenza A/HK virus. SP-303 was toxic to mice at 16 mg/kg per day as indicated by weight loss and a decrease in the duration of survival compared to control animals. From these data, a maximum therapeutic index (T.I.) of 12 was calculated. SP-303 given 3–4 days at dosages of 1.3–9.8 mg/kg per day was effective in reducing the pulmonary titer of RSV in infected cotton rats. However, at the 18.7 mg/kg per day dose a significant weight loss compared to control animals was observed; a T.I. of ⩽ 14 was estimated. These experiments demonstrate that aerosol administration of SP-303 was effective in the treatment of influenza A-infected mice and of RSV-infected cotton rats.