ABSTRACT
<p><b>OBJECTIVE</b>To identify antiviral activity of Toddalia asiatica against influenza virus type A in vitro.</p><p><b>METHOD</b>More than two hundred Chinese medicinal herb extracts were screened for antiviral activities against influenza A/PR/8/34 (H1N1) virus using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay for virus induced cytopathic effect (CPE) in a primary screening. Positive samples were picked up and were subjected to quantitative real-time polymerase chain reaction (PCR) to quantify reduction of H1N1 virus genomic RNA.</p><p><b>RESULT</b>Toddalia asiatica showed potent antiviral activities against H1N1 virus, with 50% effective concentration (EC50) value of 4.7 mg x L(-1) in MTS assay and 0.9 mg x L(-1) in quantitative PCR assay respectively. The cytotoxicity test of Toddalia asiatica generated a CC50 value of 187.2 mg x L(-1) and a selective index (SI) larger than 206 in quantitative PCR. Although the best antiviral activity of Toddalia asiatica was observed with co-treatment of influenza virus infection, it remained effective even when administrated 24 h before and after the initiation of infection.</p><p><b>CONCLUSION</b>The results suggested that Toddalia asiatica compound extract could be a candidate for anti-H1N1 virus agent in the treatment of influenza.</p>