"The FDA approvals of Mylan's Glatiramer Acetate Injection 20 mg/mL and 40 mg/mL as AP-rated, substitutable generics for Copaxone 20 mg/mL and 40 mg/mL, respectively, mark another significant milestone for our company, reinforce our proven capabilities in bringing complex and difficult-to-manufacture products to market, and further our commitment to providing access to high quality medicines", Mylan CEO Heather Bresch said in a statement.

Mylan's announcement came shortly after the FDA unveiled a series of new measures created to speed up the time it takes generic versions of complex drugs to reach the market.

Mylan (MYL) shot to the top of the S&P 500 today after the FDA approved its generic version of Teva Pharmaceutical Industries (TEVA) multiple-sclerosis drug Copaxone.

Mylan N.V. also notes that the FDA approval letter points out that it was one of the first companies to submit an Abbreviated New Drug Application with a Paragraph IV certification.

The FDA gave its approval to both of Mylan's two doses of 20mg and 40mg for its version of Copaxone that generated sales during just the second quarter of 2017 of over $1.02 billion.

Teva's US listed shares dropped 13.7% after Mylan became the top gainer on the S&P 500 before the opening bell.

Wells Fargo analyst David Maris said that optimistically the drug could add 13 cents a share to Mylan's quarterly earnings going forward.

Momenta Pharmaceuticals and the Sandoz unit of Novartis already sell a generic version of 20 mg Copaxone and are developing a version of the 40 mg dosage.

One analyst on Wall Street said this news adds to what was already a challenging short term setup for Teva, with the businesses generic segment in the US under heavy pressure, very high levels of leverage, as well as limited clarity for drivers of a wide ranging recovery in its results.

In September, Teva announced that it was seeking other drug makers it could team up with to develop opportunities in its pipeline as it struggled to keep its head above water amid mounting debts and expiring patents. The moves came as the agency attempts to deal with the rising cost of drugs in the U.S.