—In an action to recover damages for medical malpractice, the defendants separately appeal from an order of the Supreme Court, Kings County (Clemente, J.), dated February 25, 1991, which granted the plaintiff’s motion *617for leave to serve an amended complaint and an amended bill of particulars.
Ordered that the order is reversed, as a matter of discretion, with one bill of costs payable to the defendants appearing separately and filing separate briefs, and the plaintiffs motion is denied.
The Supreme Court improvidently exercised its discretion in permitting the plaintiff to serve an amended complaint and amended bill of particulars under the circumstances herein (see, Bertan v Richmond Mem. Hosp., 106 AD2d 362). The proposed amendments would clearly result in undue prejudice to the defendants by adding additional instances of alleged malpractice with which "the defendants cannot be charged with having received fair warning” (Daud v Forest & Garden Apts. Co., 178 AD2d 578, 580). Additionally, "there seems little doubt that if this amendment is permitted the defendants will have to substantially reorient their defense” (Daud v Forest & Garden Apts. Co., supra, at 580). Revising the defense will be difficult, given that the alleged instances of malpractice occurred more than 15 years ago. Mangano, P. J., Sullivan, O’Brien, Ritter and Pizzuto, JJ., concur.