Cefdinir is an antibiotic used to treat many different types of bacterial infections in children. You might see a brand name such as Omnicef on the label. You might see a brand name such as Omnicef on the label. If you put it into her milk, she will not get it all if she doesn't drink her whole bottle. Then you don't know how much she got so you can't dose her again. Best Answer: Severe diarrhea is a side effect of the Omnicef. My child had it at 8 months for double year infection, and sinus. The soft stool (watery in the beginning), lasted for three months - younger child, younger undeveloped gut, I guess. How Do I Get a 2 Year Old to Take Augmentin? Updated on June 02, 2007 J.C. We switched to Omnicef. She has had this in the past and took it quite well. Now we just need to have her trust us again when we give it to her. At this point we can't get her to even eat. It's nice to know we weren't crazy with having trouble getting her to take Augmentin. We begged the pediatrician on call to Rx. Do not take Omnicef if you are allergic to cefdinir, or to similar antibiotics, such as Ceftin, Cefzil, Keflex, and others. Before taking Omnicef, tell your doctor if you are allergic to any drugs (especially penicillin). Once-daily dosing has not been studied in skin infections; therefore, OMNICEF for Oral Suspension should be administered twice daily in this infection. OMNICEF for Oral Suspension may be administered without regard to meals. If I am correct Omnicef is an antibiotic and that is what is probably causing the diarrhea. But I would take her to the Dr. if she has had it for that long. How to use Omnicef Suspension For Reconstitution. Take this medication by mouth with or without food as directed by your doctor, usually once a day or twice a day (every 12 hours).