Objective: to analyze the impact of guidelines regarding errors in medications prescribed for administration through enteral tubes. Method: quantitative study, in three phases, undertaken in internal medicine, neurology and an intensive care unit in a general teaching hospital. In Phase 1, the following was undertaken: a protocol for dilution and unit-dose repackaging and administration for 294 medications via enteral tubes; a decision flowchart; operational-standard procedures for dilution and unit-dose repackaging of oral pharmaceutical forms and for administration of medications through enteral tubes. In phase 2, errors in 872 medications prescribed through enteral tubes, in 293 prescriptions for patients receiving inpatient treatment between March and June, were investigated. This was followed by training of the teams in relation to the guidelines established. In Phase 3, pharmaceutical errors and interventions in 945 medications prescribed through enteral tubes, in 292 prescriptions of patients receiving inpatient treatment between August and September, were investigated prospectively. The data collected, in a structured questionnaire, were compiled in the Microsoft Office Excel(r) program, and frequencies were calculated. Results: 786 errors were observed, 63.9% (502) in Phase 2, and 36.1% (284) in Phase 3. In Phase 3, a reduction was ascertained in the frequency of prescription of medications delivered via enteral tubes, medications which were contraindicated, and those for which information was not available. Conclusion: guidelines and pharmaceutical interventions were determined in the prevention of errors involving medications delivered through enteral tubes.