Patient will be administered therapeutic agent (antibiotic) or placebo in form of intravenous infusion 60 minutes prior the surgical procedure due to suspicion of the above mentioned diagnosis. If the surgery lasts for more than 3 hours, the infusion will be repeated. After analysis of the most common pathogens in individual clinical diagnosis, microbiologist chose following preparations: Acute appendicitis - Cefuroxim (Zinacef 1.5 g) + Ornidazol (Avrazor 1g), perforated ulcer - Aminopenicillin + inhibitor (Amoksiklav 2.4 g) + Fluconazole 800mg i.v., ileus of small bowel - Cefuroxim (Zinacef 1.5 g) + Metronidazol (Avrazor 1g). Surgeon will confirm the definite diagnosis during surgery which will confirm the definite inclusion in the study. Surgeon will not be present dilution or administration of the agent. Nobody from patient's attending study personnel will not be able to distinguish whether the patient was administered antibiotic or saline solution. The prophylaxis will be extended for 24 hours in common half-dosage according to publication sources.