Shares of the pharmaceutical firm Mylan (MYL - Get Report) were surging over 16% in pre-market trading on Wednesday after the FDA approved its generic version of Teva Pharmaceutical's (TEVA - Get Report) top-selling multiple sclerosis drug, Copaxone.

Shares of Teva were sinking over 15% in pre-market trading on Wednesday following Copaxone's approval. Teva reported that in its second-quarter, sales of Copaxone were responsible for $1.02 billion.

The drug's approval follows recent comments from the FDA pledging to speed up the rate of approval of generic versions of drugs, to help patients deal with the rising costs of medicines.

"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," said Mylan CEO Heather Bresch. 

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