Introduction: The use of inadequate dosage forms for pediatrics, also known as off-label use, may lead to unsafe drug therapy. In the hospital environment, especially in Pediatric Intensive Care Units, there is a high prevalence of prescriptions with drugs not suitable for children, among them antimicrobial agents, due to the severity of the infections, the critical state of the hospitalized patients, more accomplishment of invasive procedures and a higher incidence of resistant bacteria. In general, the use of antimicrobials in children, as well as other pharmacological groups, has been based mainly on extrapolations and adaptations of the use in adults. This information was obtained from rare observational studies and consensus of specialists in the area. Due to the critical condition of patients, the complex therapies involving antimicrobial agents are not always adequately done, which may cause harm to the patients' health and also contribute to bacterial resistance. Objective: To evaluate the incidence of antimicrobial use in patients hospitalized in a Pediatric Intensive Care Unit. Method: A crosssectional study conducted at the Pediatric Intensive Care Unit of the municipality of Rio Branco, Acre, from August 2014 to July 2015. The sample consisted of 246 children from zero to eleven years old and hospitalized with any pathologies. The prescriptions of the first 24 hours were analyzed. The use of off-label antimicrobials and potential drug interactions with these drugs was investigated. Results: Two hundred and thirty-one children (93.9%) received the prescription of at least one antimicrobial. The most commonly prescribed antimicrobial agent was ceftriaxone. On average, each patient received two antimicrobials. In 66.8% of cases, there was an off-label use, with the prescribed dose being higher than recommended in 41% of the cases. In 56% of prescriptions there was at least one potential drug interaction involving antimicrobials. Ampicillin and gentamicin were the antibiotics most involved in interactions. Conclusions: the high frequency of off-label use and potential drug interactions involving antimicrobials was confirmed in this study. Treating children as young adults may expose these patients to adverse drug events that compromise the safety of this particular group of patients. That points to the need for multidisciplinary teams to work together and be encouraged to carry out more studies that ensure the safety of use of medication in pediatrics.