Because of the mechanism of action of the cephalexin , it is not indicated for the treatment of trich. Best Answer: He's in for it. Cephalexin is not effective against trichomonas. He needs either a 2 gram dose of metronidazole or tinadazole, or. Can you treat tricomoniasis w/ Doxycycline or keflex?. Trichomoniasis can usually be cured with prescription drugs, either metronidazole or tinidazole,.