Abstract: Intra-abdominal infections in children are defined as inflammatory processes affecting the peritoneal cavity and its organs, in response to the presence of microorganisms or their toxins. They comprise the most severe bacterial infections in children, frequently presenting a complicated clinical course. The increasing antibiotic resistance of pathogens and the scarcity of new antimicrobial drugs force the search for new therapeutic options and drug combinations in combination therapy. Fosfomycin represents one of the oldest antibiotics, which in Poland is particularly known for its use in the treatment of urinary tract infections. It has only recently become available in the intravenous form; however, this dosage form shows different properties, which significantly extends the indications for the use of this drug also in the treatment of severe infections in various age groups. The bactericidal effect of fosfomycin is manifested by inhibiting the synthesis of the bacterial cell wall with an extremely broad spectrum of activity. It is effective against gram-negative and gram-positive bacteria, including the strains broadly resistant to other antibiotics. This paper presents four clinical cases of fosfomycin use in children presenting with complicated intra-abdominal infections. Three patients showed improvement in their general condition and in the treatment of the infection, whereas fosfomycin was ineffective in one individual. The complicated course in the described case reports involved multidirectional and systemic treatment, although the positive effect of fosfomycin in combination with another antibiotic in the treatment of peritonitis is encouraging and suggests more extensive use of this antibiotic in the treatment regimens of intra-abdominal infections.

Key words: bacterial infections, combination therapy, fosmomycin, intensive care unit, intra-abdominal infections in children