(Yicai Global) Oct. 28 -- Ascletis Pharma’s shares closed lower today after surging in the wake of the Chinese biotech firm saying a unit will supply Pfizer with the antiretroviral medicine ritonavir for its Covid-19 antiviral therapy in China.

Ascletis Pharma [HKG: 1672] ended down 4.2 percent at HKD2.54 (32 US cents) a share today, after surging almost 15 percent in the early afternoon following the announcement. The benchmark Hang Seng Index slumped 3.7 percent.

Under a five-year deal, Ascletis Pharma Zhejiang will make and supply 100-milligram ritonavir film-coated tablets to Pfizer China for use in the Chinese mainland as part of its Paxlovid treatment, the unit’s Hangzhou-based parent company said in a filing to the Hong Kong Stock Exchange. The amounts supplied will depend on purchase orders placed by Pfizer China over the period.

Paxlovid is an antiviral medicine to treat adults with mild to moderate Covid-19 who are at high risk. It has two active pharmaceutical ingredients: nirmatrelvir and ritonavir. 

Founded in 2013, Ascletis Pharma was the first no-revenue biotech company to launch an initial public offering in Hong Kong in 2018.

Editor: Martin Kadiev