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The aim of our work is to determine the susceptibility of clinical isolates of bacteria in biofilm to the most common antimicrobial drugs used in clinical practice. Materials and methods. By means of serial dilutions of antimicrobial drugs, we analyzed the effectiveness of amoxicillin clavulanate, ceftriaxone, cefixime, gentamicin, furazidin and silver nanoparticles on planktonic and biofilm forms of 60 strains of bacteria isolated from children with lower urinary tract infections, acute and chronic pyelonephritis. Results. Through the use of serial dilutions method it was found that 77 % of planktonic strains were susceptible to amoxicillin clavulanate, 70 % – to ceftriaxone, 47% – to cefixime, 78 % – to gentamicin and 92 % – to furazidin. The percentage of the strains susceptible to amoxicillin clavulanate after biofilm formation was 63 %, to ceftriaxone – 17 %, to cefixime – 13 %, to gentamicin – 37 %, to furazidin – 80 %. Conclusions. It was established that biofilm bacteria gain resistance to all the investigated drugs, but the change of susceptibility manifests itself in varying degrees. The number of resistant strains of bacteria depends on the form of the urinary tract infection, in acute and chronic pyelonephritis the number of resistant strains is much greater than in infection of the lower urinary tract. Planktonic and biofilm forms of bacteria were the most effectively influenced in vitro by furazidin, amoxicillin clavulanate and gentamicin. Cephalosporins (ceftriaxone, cefixime) were less effective against both forms of bacteria.