(Reuters) - The U.S. Food and Drug Administration on Monday approved a bone-building drug from Pfenex Inc to treat osteoporosis in certain patients at high risk for fractures, giving the company its first commercial product.

The company said it is seeking the FDA’s authorization to designate the drug, PF708, as therapeutically equivalent to Eli Lilly and Co’s injectable drug Forteo.

This would permit PF708 to be automatically substituted for Forteo, which lost its market exclusivity in many U.S. states in August.

Pfenex hopes to market PF708 as a cheaper option for Forteo, which brought in global revenue of $1.58 billion last year.

Pfenex said it was conducting a comparative study between PF708 and Forteo and expects to submit a final report to the FDA as early as the second half of October.

“We currently expect our commercial partner Alvogen to launch PF708 upon an FDA decision on the therapeutic equivalence rating,” Pfenex Chief Executive Officer Eef Schimmelpennink said in a statement.

Analysts at William Blair expect PF708 to bring in sales of $96.1 million at its peak in 2021.

The company will receive a $2.5 million milestone payment from privately owned Alvogen for gaining U.S. approval.