Hi, Thanks for asking in Healthcare Magic. Skifi and Topcef are Brand names of the antibiotic Cefixime, used in lung infections. Cefixime is the chemical name of the drug. It is a third generation cephalosporin effective against many virulent bacteria. Having started a course of antibiotic, preferably one should complete it with the same formulation of a company as oral formulations of different company will have different bioavailability. Bioavailability is the rate and extent of drug absorption. It can decide the success or failure of an antibiotic therapy. Your delay in period may not be due to Cefixime. Stress can delay period and so don t be anxious. Illness, anemia can also cause the delay. Eat nutritious diet, correct anemia and take vitamin supplements. I hope this is helpful to you.