The protocol will be submitted for review by the Research Committee and the Ethics Committee of the Regional University Hospital of Colima. Upon receiving approval, a double-blind, placebo-controlled, randomized clinical trial will be carried out, based on CONSORT guidelines. This trial involves the participation of pediatric patients aged 4 to 18.
Patients will be selected from those attending private practice and satisfying Rome IV criteria for any of the Functional Abdominal Pain Disorders (FAPD). Before any intervention takes place, the purpose and procedures of the study will be explained to both the patients and their legal guardians. If they decide to participate, they will be asked to sign an informed consent letter and assent form for minors. Patients will be selected through stratified probabilistic sampling in 4 categories (Irritable Bowel Syndrome, Functional Dyspepsia, Abdominal Migraine, and Functional Abdominal Pain not otherwise specified (FAP-NOS)) until the desired sample size of 82 participants is reached. Once participants are selected, they will be randomly assigned to one of the three groups: trimebutine/probiotic, probiotic/placebo, or trimebutine/placebo, with each group consisting of at least 20 participants. The initial diagnosis will be carried out using the Rome IV Criteria Questionnaires for pediatric patients, and the intensity of pain will be evaluated using the Visual Analog Scale (VAS) and quality of life with PedsQL 4.0. Patients will be administered the treatment corresponding to their assigned group and will be clinically followed up at 4 and 8 weeks. During these follow-up consultations, the Rome IV Criteria Questionnaires and scales will be reapplied to assess the evolution of the patients' symptoms and their response to treatment. Any patient who requests voluntary withdrawal, those with treatment adherence less than 80%, and those participating in another study or being treated by another physician simultaneously will be removed from the study.
Statistical analysis will be carried out using international Business Machine (IBM®) Statistical Package for the Social Sciences (SPSS®) Statistics 26. Descriptive statistics with measures of central tendency will be used, presenting the results in tables and graphs. To determine whether the data follow a normal distribution, the Kolmogorov-Smirnov and Shapiro-Wilk tests will be applied. Measurements in 3 groups (trimebutine, probiotics, and control) and at 3 times (0, 4, and 8 weeks) will be analyzed. For intervening categorical variables like gender and education, the chi-square test (X2) will be used. For continuous variables like age and BMI, the Mann-Whitney U test will be applied, expecting statistically significant differences with p \< 0.05.
If the data follow a normal distribution, repeated measures ANOVA will be used to compare the means of the 3 groups (trimebutine, probiotics, and placebo). McNemar's test or the sign test will be considered as secondary analyses to evaluate changes within each group over time (0, 4, and 8 weeks). If the data do not follow a normal distribution, non-parametric tests like the Friedman test will be employed.
In case of finding a statistically significant difference in repeated measures ANOVA or the Friedman test, post hoc tests will be performed to identify specific differences between groups and times. If necessary, correlation tests like Pearson or Spearman will be used to evaluate relationships between different variables within the study.
