GI Medications
Acid, nausea, motility, bowels and the liver
| Drug | Key points |
|---|---|
| Antacids | Calcium carbonate (Tums): constipation. Magnesium hydroxide: diarrhea; avoid in kidney failure. Aluminum hydroxide: constipation. Take 1–3 h after meals and at bedtime; separate from other drugs by 1–2 h (they bind many drugs). |
| H2 blockers (-tidine) | famotidine. Before meals or at bedtime. Confusion in older adults (cimetidine has many interactions). |
| PPIs (-prazole) | omeprazole, pantoprazole. 30–60 min before breakfast. Long-term: C. diff, pneumonia, fractures, low Mg²⁺, low B12. Use the lowest dose for the shortest time needed. |
| Sucralfate | Coats ulcers. Empty stomach 1 h before meals; separate other meds by 2 h; constipation. |
| Misoprostol | Protects the stomach during NSAID use. Causes miscarriage: not in pregnancy (unless used obstetrically); reliable contraception. |
| Ondansetron | Antiemetic. QT prolongation, headache, constipation. |
| Metoclopramide | Dopamine blocker that speeds stomach emptying (prokinetic) and stops nausea. Boxed warning: tardive dyskinesia: avoid use >12 weeks. EPS, drowsiness. Avoid in Parkinson's and bowel obstruction. |
| Promethazine | Sedation, respiratory depression in children <2 (contraindicated). IV: severe tissue injury: deep IM preferred. |
| Lactulose | Hepatic encephalopathy: pulls ammonia into the gut. Goal 2–3 soft stools a day; watch K⁺ and fluid. Often combined with rifaximin. |
| Loperamide | Not for bloody diarrhea, fever, or C. diff. High doses → dangerous heart rhythms. |
Laxatives
| Bulk-forming (psyllium) | With a full glass of water; 1–3 days |
| Osmotic (polyethylene glycol, lactulose) | 1–3 days; bowel prep (large-volume PEG) |
| Stimulant (senna, bisacodyl) | 6–12 h; for opioid constipation. Don't crush bisacodyl or take with milk/antacids |
| Softener (docusate) | Weak on its own |
H. pylori
Combination therapy for 14 days: a PPI + antibiotics (often bismuth quadruple therapy: PPI, bismuth, tetracycline, metronidazole). Bismuth turns stools and tongue black (harmless). Test for cure afterwards.
IBD
Aminosalicylates (mesalamine), steroids, immunomodulators, and biologics (infliximab, adalimumab, vedolizumab, ustekinumab): screen for TB and hepatitis B before biologics; no live vaccines.