, 2003, Hsu et al., 2003 and Poutanen et al., 2003). Another broad spectrum antiviral agent, ribavirin, a purine nucleoside analogue that inhibits guanosine triphosphate synthesis and viral RNA polymerase activity, was commonly given to patients in Asia and North America. Of 2546 patients with descriptions of medical treatment for SARS reported in the literature, 1316 (51.7%) of them received ribavirin, either as the primary treatment regimen or in combination with a corticosteroid this website or other antiviral agent such as lopinavir/ritonavir

(Table 2). The regimens of ribavirin included: • intravenous formulation of 8 mg/kg every 8 h for 14 days; However, the role of ribavirin remained uncertain, as there was no obvious clinical benefit in a retrospective, uncontrolled cohort analysis involving 229 patients in Singapore

(Leong et al., 2004). Although in vitro studies also demonstrated that ribavirin had no significant activity against SARS-CoV in Vero cells ( Cinatl et al., 2003), ribavirin had good activity when it was tested in human Caco-2 and pig kidney cell lines ( Morgenstern et al., 2005). Moreover, ribavirin was shown to be synergistic with interferon in in vitro combination assays ( Chen et al., 2004). The low level of in vitro activity MEK activation against SARS-CoV might be attributed to cellular toxicity, as the 50% cytotoxic dose of ribavirin on various cell lines has been reported to be approximately 200–1000 μg/mL ( Tan et al., 2004). Adverse effects of ribavirin were not uncommon. In a cohort of 110 patients in Toronto, dose-related hemolytic anemia was observed in 61% of patients, whereas hypocalcaemia and hypomagnesaemia was reported in 58% and 46% respectively ( Knowles et al., 2003). In another

cohort of 44 patients in Taiwan, 73% of patients had a drop in hemoglobin Silibinin level 3 days after therapy with ribavirin which was found to be an independent prognostic factor of hypoxemia or mortality ( Chiou et al., 2005). Some patients were treated with a boosted HIV protease inhibitor, with a combination of lopinavir and ritonavir as either initial therapy or rescue therapy along with ribavirin in the evolving epidemic (Chan et al., 2003 and Chu et al., 2004a). In vitro antiviral susceptibility testing showed that the cytopathic effect of SARS-CoV was inhibited by lopinavir at 4 μg/ml and ribavirin at 50 μg/ml after 48 h of incubation. Inhibition of the cytopathic effect was achieved down to a lopinavir concentration 1 μg/ml combined with ribavirin 6.25 μg/ml, only when the viral inoculum was reduced to 50 TCID50 or below, suggesting potential synergistic activity ( Chu et al., 2004a). The addition of lopinavir/ritonavir as initial treatment was associated with a reduction in the overall death rate (2.3%) and intubation rate (0%), when compared with a matched cohort who received standard treatment with ribavirin (15.6% and 11.0% respectively, P < 0.05).