Shares of Aceto Corp. plummeted 49% toward a 15 1/2-year low ahead of Thursday's open, enough to pace the premarket decliners, after the developer health products and pharmaceutical ingredients maker said it was negotiating credit agreement waivers with its lenders, cutting its dividend, taking a large impairment charge and initiating an evaluation of strategic alternatives. The company also said late Wednesday investors should no longer rely on the profit and sales guidance provided in February, and that Chief Financial Officer Edward Borkowski resigned. The stock was on track to open at the lowest level seen during regular session hours since Nov. 13, 2002. Aceto said it was addressing "persistent adverse conditions in the generics market," which resulted in "intense" competitive and pricing pressures. Aceto said it expects to record impairment charges of $230 million to $260 million on certain marketed and pipeline generic products, and that it expects to make a "significant reduction" of its dividend to help fortify its balance sheet, and provide assurances to its lenders. The stock had plunged 28.4% year to date through Wednesday, while the S&P 500 had gained 1.3%.