Gastrointestinal Drugs and Antacids

Gastrointestinal, Antiemetic, and Antispasmodic Drugs

Antihistamines

• Cimetidine: an antiulcer agent (histamine H2-receptor antagonist) that can decrease acid secretion
• Indications:
  • Peptic ulcers
  • GERD
  • Prophylaxis of pulmonary aspiration in anaesthesia
  • Gastritis in combination with other agents (e.g. antacids)
• Usual presentation: 200mg tablet
• Dosage and duration:
  • 200-400mg single dose 1hr before operation/anaesthesia
  • 200mg BD to TDS up to 3 days to 2 weeks
  • Child dose: 10-20mg/kg/day (in divided doses)
• Adverse effects:
  • Gynecomastia (0.3-4%)
  • Antiandrogen: may cause feminization and sexual dysfunction in males
  • Diarrhea, headache, dizziness, skin rash, fever (less than 2%)
• Remarks:
  • Sometimes comes in injectable form
  • Pregnancy: may be acceptable
  • Lactation: not recommended

Ranitidine

• Discontinued in some countries
• Usual presentations:
  • Injection: 25mg/ml of 2ml ampoules
  • 75, 150, or 300mg tablets
• Indications:
  • Gastroesophageal reflux disease
  • Gastric ulcer, benign
  • Esophagitis, gastritis
• Usual dosages and duration:
  • 150mg PO BD or TDS
  • 50mg IM/IV 12hrly or up to 6hrly
  • Child dose: 5-10mg/kg/day once or 12hrly
  • According to clinical response. If not responsive, use PPIs
• Adverse effects and cautions:
  • Headache (3%)
  • Use with caution in renal and hepatic impairment
  • IM administration does not need to be diluted, but IV injection is better diluted to make 20cc
• Remarks:
  • Pregnancy: may be acceptable
  • Lactation: contraindicated