ZENITH LABS <ZEN> WILL REPORT 4TH QTR LOSS Zenith Laboratories Inc said the company will report a fourth quarter loss, and the amount will be determined on completion of its year end audit. The company did not elaborate further. For the third quarter ended Sept 30, 1986, Zenith reported a loss of 3,451,000 dlrs or 16 cts per share, adjusted for a May 1986 2-for-1 stock split. The company also said it received Food and Drug Administration approval to market Cefadroxil, a generic version of an antibiotic with domestic sales exceeding 50 mln dlrs in 1986. Zenith said it will not market the drug until "questions relating to the applicability of certain patents have been resolved."