Teva Pharmaceutical Industries has offered to buy NuPathe, topping an already-agreed bid from Endo Health Solutions for the migraine specialist.

A definitive agreement was signed at the end of last year whereby Endo would pay $2.85 per share in cash, which equates to $105 million. The deal would give Endo access to NuPathe's migraine treatment Zecuity (sumatriptan), the only US Food and Drug Administration-approved migraine patch, and NuPathe shareholders would get rights to additional cash payments of up to $3.15 per share if sales of the patch meet expectations.

However, the Israeli major has now come in with a bid of $3.65 per share, and is also offering an extra $3.15 a share if Zecuity sells well. That package would be worth about $150 million in total.

Teva had previously been in negotiations with respect to a co-promotion and clearly likes what it sees. NuPathe said in a filing to the US Securities and Exchange Commission that "after review and discussion, the company board determined that the Teva proposal is reasonably expected to lead to a superior proposal".

That may not necessarily be the case, according to some observers who cite the different additional terms offered by Endo and Teva. The latter's proposal would give NuPathe shareholders $0.85 per share when annual sales of Zecuity reach $100 million, another $1.00 when they hit $300 million and another $1.30 if they $450 million.

Endo's offer would see NuPathe shareholders bank $2.15 per share when Zecuity sales exceed $100 million. They would get the remainder if that figure goes past $300 million.