NutriSystem ( NTRI) plunged 10% in heavy trading as a long-running selloff in the weight-loss company accelerated. The stock has dropped 22% in two weeks as technical sell signals have been struck. Shares dropped $4.83 to $53.01. Odyssey Healthcare ( ODSY) dropped 7% after the hospice operator issued subpar 2007 guidance. Shares fell $1 to $12.12. ICU Medical ( ICUI) sank 6% after the critical care company issued disappointing guidance for the coming year. Shares slid $2.52 to $37.50. Theragenics ( TGX) soared 19% after swinging to a fourth-quarter profit. Shares rose 66 cents to $4.12. Wyeth ( WYE) dropped 2% after posting a 17% rise in fourth-quarter earnings. Shares fell 96 cents to $49.64. Among healthcare stocks gaining ground Tuesday, Amgen ( AMGN) rose 94 cents to $70.91, Elan ( ELN) added 13 cents to $12.43 and Biogen ( BIIB) tacked on 33 cents to $48.01. Among decliners, Merck ( MRK) slid 55 cents to $44.96 and Cephalon ( CEPH) gave up 38 cents to $73.85.