This infant has persistent vomiting with feeding-associated distress and poor weight gain, despite appropriate initial nonpharmacologic measures (thickened feeds and hypoallergenic formula). MCCQE pediatrics objectives emphasize distinguishing physiologic reflux (“happy spitter”) from gastroesophageal reflux disease (GERD), which is suggested by feeding aversion/crying and failure to thrive. When conservative strategies fail and GERD is causing significant symptoms or complications (e.g., poor growth, suspected esophagitis contributing to irritability and possibly anemia), escalation to acid suppression is appropriate; a proton pump inhibitor such as omeprazole is used to treat acid-related esophageal injury and improve symptoms in selected infants with suspected erosive disease.

Metoclopramide is not preferred due to limited benefit and risk of extrapyramidal adverse effects. Calcium carbonate antacids are not recommended as ongoing therapy in infants due to safety concerns and inferior efficacy for esophagitis. Bismuth sulfate is not indicated. Loperamide is inappropriate and potentially harmful in infants. Continued monitoring of growth and reassessment for alternative diagnoses or alarm features is essential.