A compound found in the root of the liquorice plant could be more effective at treating the SARS virus than currently used drugs, reported researchers from the Institute of Medical Virology at Frankfurt University Medical School in this week's Lancet.
Since the outbreak of SARS at the end of last year, scientists have been searching for active antiviral compounds to treat the disease. The German researchers assessed the antiviral activities of five different compounds - ribavirin, currently used to treat the virus, 6-azauridine, pyrazofurin, mycophenolic acid, and glycyrrhizin, found in the liquorice root - against two samples of coronavirus (FFM-1 and FFM-2) from patients with SARS admitted to the clinical centre of Frankfurt University. The most potent inhibitor of the SARS virus was glycyrrhizin, they said.
"Our findings suggest that glycyrrhizin should be assessed for treatment of SARS," write the researchers in the journal.
As well as inhibition of virus replication, glycyrrhizin was found to inhibit adsorption and penetration of the virus - early steps of the replicative cycle, reported the researchers, although they add that the mechanism of glycyrrhizin's activity against the SARS virus is unclear.
All of the compounds tested by the team are available commercially and have been used in patients for their antiviral, antitumour and immunosuppressive activity. Glycyrrhizin has previously been used to treat patients with HIV-1 and chronic hepatitis C virus.
The researchers noted that infrequent side effects such as raised blood pressure and hypokalaemia were reported in some patients after several months of glycyrrhizin treatment. However treatment of SARS should only be needed for a short time. "Since the side effects of this compound are known and can be controlled for, proper monitoring could lead to effective use of glycyrrhizin as a treatment for SARS," they write.
Compared to ribavirin, which has been shown to have many toxic effects when given to patients with SARS, high doses of glycyrrhizin had relatively few side effects and was reported to be clinically effective, said the team.
There have been around 8,500 cases of SARS worldwide since last November, including 800 deaths - mainly in mainland China, Taiwan and Hong Kong, reported the Financial Times last week.