From the history provided, I would not treat this as simple post-food diarrhoea anymore. In a 75-year-old, the combination of persistent vomiting + inability to tolerate solids/liquids + markedly reduced/absent bowel movements for about 2 days needs urgent in-person reassessment, particularly to exclude intestinal obstruction or ileus, significant dehydration/electrolyte disturbance, and medication-related gastric/intestinal problems. Persistent vomiting with inability to keep fluids down warrants urgent medical assessment.
Possible explanations
Post-infectious gastritis/gastroparesis after the diarrhoeal illness can cause nausea, early satiety and vomiting.
Ileus or intestinal obstruction is important to exclude, particularly because the diarrhoea has stopped and she is now not passing stool. If she is also not passing flatus, has abdominal distension or colicky/continuous abdominal pain, obstruction becomes particularly concerning
Dehydration and electrolyte abnormalities (especially hypokalaemia, hyponatraemia or renal dysfunction) can themselves worsen nausea, weakness and ileus. Older adults are particularly vulnerable to dehydration.
Medication effects may be contributing. Ultracet contains tramadol, which can cause marked drowsiness, nausea/vomiting and constipation, so stopping it as advised was reasonable. Other recently introduced medicines should also be reviewed.
Less commonly, pancreatitis, biliary disease, acute
kidney dysfunction, metabolic disturbances or another intra-abdominal process may present this way.
Next Steps
She may need: BP, pulse, oxygen saturation and hydration assessment Abdominal examination, including checking for distension/obstructive signs CBC,
electrolytes (Na/K), urea/
creatinine, glucose
LFT, amylase/lipase as clinically indicated ECG Abdominal X-ray and/or ultrasound/CT abdomen if obstruction or another acute abdominal pathology is suspected IV fluids and an appropriate parenteral antiemetic if she cannot retain oral fluids Further management depending on whether obstruction/ileus is found If there is suspected obstruction, do not give laxatives or force solid food until she has been assessed.