The upper endoscopy is one of the most common methods for the diagnosis and treatment of upper gastrointestinal (GI) tract diseases and provides a unique opportunity to identify early neoplastic lesions.

Before an upper endoscopy it is required a 6 hour fasting period[1]. However, even with this fasting period, sometimes the mucosal visualization, especially in the stomach, is impaired by the presence of foam, bubbles or gastric mucus.

To improve visualization of the gastric mucosa, it is possible to administrate an oral solution of defoaming agents such as Simethicone and mucolytic agents like Pronase or N-Acetylcysteine previously to the procedure.

The aim of this project is to determine if the use of premedication with simethicone, alone or in association with N-Acetylcysteine, improves mucosal visualization during an upper GI endoscopy.

a. Study type: prospective, randomized, double-blinded, placebo-controlled trial: i. Prospective inclusion of patients; ii. Randomization by computer generated tables; iii. Allocation concealment by sealed, opaque envelopes; iv. Double-blinded - nurse instructed not to reveal treatment; patient and doctor unaware of treatment;

b. Patient selection: consecutive series of patients scheduled for upper gastrointestinal endoscopy; Exclusion criteria - sedation, previous total gastrectomy, known neoplasia or stenosis, allergies to simethicone or N-acetylcysteine, therapeutic or urgent procedures;

c. Sample size: 270 (3 groups of 90 patients): to improve "excellent" preparations from 20% (value from our own database) to 40% and assuming a normal distribution and a power of 80% (α=0.05), the calculated sample size of each of the 3 groups was 82; allowing for a 10% dropout rate, the sample size is 90 (270 patients overall); Groups: Group A - 100mL of water (placebo); Group B - 100mL of water plus 100mg Simethicone; Group C - 100mL of water plus 100mg Simethicone plus 600mg N-acetylcysteine;

d. Data collection methods: form sheet filled by nurses (appendix 1) and endoscopist (appendix 2);

e. Analysed variables: patients characteristics (age, gender), indication for endoscopy, time from administration to procedure, score of mucosal visualization, side effects of medication;

f. Statistical analysis: chi-square test.

Inclusion Criteria:

• consecutive series of patients scheduled for upper gastrointestinal endoscopy
• signed informed consent

Exclusion Criteria:

• sedation
• previous total gastrectomy
• known neoplasia or stenosis
• therapeutic or urgent procedures
• allergies to simethicone or N-acetylcysteine