Patients treated with antibiotics frequently develop diarrhea. In developed countries, adults, particularly the elderly, experience a higher death rate due to diarrhea than children. <P>Results from in vitro and preliminary in vivo studies lead us to hypothesize that oral administration of recombinant human lactoferrin as a medical food might be able to prevent and reduce antibiotic associated diarrhea in adults.<P> The present fast track SBIR Phase I and II proposal plans to test this hypothesis with a clinical trial involving 260 subjects. In phase I, we will produce 25 kg of testing materials, recombinant human lactoferrin, from rice grain and at the same time obtain IRB approval of the clinical trial. <P>In phase II, we will conduct the clinical study in four test sites in Baltimore. We expect that the study will prove that recombinant human lactoferrin is able to reduce incidence of antibiotic associated diarrhea by 50% and if patients do get diarrhea, the diarrhea days will be shorten by half. <P> Public Health Relevance: The high death rate associated with diarrhea in adults compared to that in children in developed countries is commonly neglected. Oral administration of recombinant human lactoferrin might be able to prevent antibiotic associated diarrhea in adults and the present proposal is to test this hypothesis.