Hybridon Inc. on Friday said it has stopped development of its GEM91 phosphorothioate antisense oligonucleotide for treatment of HIV/AIDS, citing side effect and efficacy problems it hopes will be overcome with second-generation compounds. HYBN was down $1.625 Friday, closing the week at $3.125.

The decision came after HYBN's open label Phase II trial was halted based on analysis of data from 9 of an expected 12 patients with advanced AIDS. The patients had received 3.2 mg/kg/day of GEM91 by iv for 14 days. After 10 days of therapy, 3 of the 9 had to discontinue treatment when their platelet counts dropped below 50,000 platelets/mm
. Also, decreased levels of infectious virus seen in earlier trials were not observed in this study.