GI drugs

Sodium Bicarbonate

Antacid. Forms CO₂ thus causing gastric distention. Unreacted alkali is absorbed possibly causing metabolic alkalosis in high doses and in patients with renal insufficiency. May also cause fluid retention and is thus also contraindicated in patients with CHF and HTN. Should be taken at least 4h apart from tetracyclines, fluoroquinolones, itraconazole and iron.

Calcium carbonate

Antacid. Reacts slower than sodium bicarbonate. If used with Ca²⁺-containing dairy products, it can cause hypercalcemia, renal insufficiency and metabolic acidosis (milk-alkali syndrome). Should be taken at least 4h apart from tetracyclines, fluoroquinolones, itraconazole and iron.

Magnesium hydroxide

Antacid. Unabsorbed salts may cause osmotic diarrhea. Long-term use is contraindicated in patients with renal insufficiency. Should be taken at least 4h apart from tetracyclines, fluoroquinolones, itraconazole and iron.

Aluminum hydroxide

Antacid. May cause constipation. Long-term use is contraindicated in patients with renal insufficiency. Should be taken at least 4h apart from tetracyclines, fluoroquinolones, itraconazole and iron.

Cimetidine

H2-blocker; Due to first-pass effect, only has 50% bioavailability. Dose reduction is required for patients with moderate to severe renal insufficiency. Inhibits binding of dihydrotestosterone to androgen receptors, inhibits estradiol metabolism and increases serum prolactin and thus may cause gynecomastia or impotence in men and galactorrhea in women. This drug interferes with hepatic P450. inhibits gastric first-pass metabolism of ethanol resulting in increased levels in blood.

Famotidine

H2-blocker; Due to first-pass effect, only has 50% bioavailability. Dose reduction is required for patients with moderate to severe renal insufficiency.

Ranitidine

H2-blocker; Due to first-pass effect, only has 50% bioavailability. Dose reduction is required for patients with moderate to severe renal insufficiency. inhibits gastric first-pass metabolism of ethanol resulting in increased levels in blood. Withdrawn due to cancer risks

Nizatidine

H2-blocker; little first-pass metabolism and thus higher bioavailability. Dose reduction is required for patients with moderate to severe renal insufficiency. inhibits gastric first-pass metabolism of ethanol resulting in increased levels in blood.

Which side effects are common to all H2-blockers?

Diarrhea, headache, fatigue, myalgia and constipation. Also notable, these drugs cross the placenta and are secreted in breast milk.

Through what mechanism can H2-blockers cause cardiovascular problems?

High doses, given as rapid IV infusion can result in blockade of cardiac H2 receptors and cause Hypotension and bradycardia; Which is why IV H2-blockers should be administered over a timespan of at least 30 minutes.

Omeprazole

PPI. Oral. Shortest half-life. Metabolized by hepatic P450. May inhibit the metabolism of warfarin, phenytoin and diazepam.

Lansoprazole

PPI. Oral. Metabolized by hepatic P450. May enhance clearance on theophylline.

Rabeprazole

PPI. Oral. Metabolized by hepatic P450. no drug interaction.

Pantoprazole

PPI. Oral and IV. Highest in bioavailability. Metabolized by hepatic P450. No drug interaction.

Esomeprazole

PPI. Oral and IV. Metabolized by hepatic P450. May inhibit the metabolism of diazepam.

Dexlansoprazole

PPI. Oral.

Sucralfate

Sucrose salt complexed to sulfated aluminum hydroxide. After breakdown, sucrose sulfate binds to proteins present at the ulcer base creating a physical barrier -which lasts up to 6h- and stimulating mucosal prostaglandin and bicarbonate secretion. Indicated in pregnancy GERD. ADRs include constipation, nausea, dry mouth and rash. Long-term use is contraindicated in patients with renal insufficiency because of aluminum absorption. During the fist 2h of ingestion, might bind to other medication.

Misoprostol

Analog of PGE1. Oral, rapidly absorbed and metabolized. Half-life is less than 30min hence, it must be taken 3-4 times daily. Reduces the incidence of NSAID-associated ulcers and ulcer complication. Adverse effects include abdominal pain and stimulation of uterine contractions. Contraindicated in pregnant women and women of childbearing age.

Bismuth compounds

Include Bismuth subsalicylate (OTC) and Bismuth subcitrate potassium (only used in combination with metronidazole and tetracycline for H. pylori eradication). Creates a protective layer and stimulates mucus, PG and bicarbonate secretion.

Bismuth subsalicylate

Inhibits intestinal PG and Cl^- secretion and thus helps in acute infectious diarrhea. Binds to enterotoxins. Harmlessly blackens stool and darkens the tongue. Contraindicated for long use and in patients with renal insufficiency. Long term use may cause encephalopathy (ataxia, headache, confusion and seizures.

What drug regimen is recommended for eradication of H. pylori?

PPI or bismuth compound + two of the antibiotics below:

Amoxicillin, tetracycline, clarithromycin, metronidazole

Regimens: OCA (10 days), LAC (14 days), OC (O 30 days, C 14 days), LCM and OCM (both 14 days).

Bethanechol

Cholinomimetic prokinetic. Formerly used to treat GERD and gastroparesis.

Neostigmine

AChE inhibitor. Enhances Lower GI emptying. IV used for acute large bowel distention (AKA Pseudo-obstruction or Ogilvie’s syndrome). ADRs are excessive salivation, nausea, vomiting, diarrhea and bradycardia.

Erythromycin

This drug and other macrolides induce GI motility by stimulating motilin receptors. IV form is indicated for gastroparesis. Down side is it quickly builds tolerance.

Which drug classes are used in IBD?

Amino salicylates, Glucocorticoids(Budesonide, prednisone or prednisolone oral, rectal and IV), Purine analogs, MTX, Anti-TNF and Anti-integrins.

Amino salicylate names

Sulfasalazine, Olsalazine (induces secretory diarrhea), Balsalazide and Mesalamine (AKA 5-ASA, absorbed well by the small intestine and poorly by the colon). All these drugs work topically.

Azathioprine

Purine antimetabolite with immunosuppressive properties. Nausea, vomiting, bone marrow depression and hepatotoxicity. Should not be prescribed with allopurinol without careful monitoring.

6-mercaptopurine

Purine antimetabolite with immunosuppressive properties. Higher bioavailability than azathioprine. Nausea, vomiting, bone marrow depression and hepatotoxicity. Should not be prescribed with allopurinol without careful monitoring.

Natalizumab

Anti-integrin, Ab against alpha4 subunit of integrin which exists in the CNS. Prevents adhesion and thus migration of Leukocytes to the site of infection.

Which classes of drugs are used for the treatment of diarrhea?

Opioid agonists and bile salt binding resins.

Loperamide

Nonprescription opioid agonist. Does not cross the blood-brain barrier. Has not analgesic effects or addiction potential. Does not build tolerance. taken 4 times daily orally.

Diphenoxylate

Prescription opioid agonist. No analgesic effect in standard doses. Prolonged use can cause dependence. Mixed with atropine to prevent overdosage. Contraindicated in gut infections.

Cholestyramine

Bile salt resin. Available in powder and pill forms. Taken 1-3 times daily before meals. ADRs are bloating, flatulence, constipation and fecal impaction. Should be taken 2h apart from any other drug as they bind together.

Colestipol

Bile salt resin. Available in powder and pill forms. Taken 1-3 times daily before meals. ADRs are bloating, flatulence, constipation and fecal impaction. Should be taken 2h apart from any other drug as they bind together.

Colesevelam

Bile salt resin. Available in powder and pill forms. Taken 1-3 times daily before meals. ADRs are bloating, flatulence, constipation and fecal impaction.

Dicyclomine

Anticholinergic antispasmodic. At high doses these drugs cause dry mouth, visual disturbances, urinary retention and constipation. used in IBS.

Hyoscyamine

Anticholinergic antispasmodic. At high doses these drugs cause dry mouth, visual disturbances, urinary retention and constipation. used in IBS.

Alosetron

Antidiarrhea. 5-HT3 antagonist used for treatment of IBS with diarrhea in women.

Lubiprostone

Laxative. Type 2 Cl^- channel activator used for treatment of IBS with constipation in women.

Linaclotide

Laxative. Activates Guanylyl cyclase-C on the luminal surface of the intestine causing type 2 chloride channels to activate.

Pancreatin

Oral Pancreatic lipase extracted from pigs. Enteric-coated capsules.

Pancrelipase

Oral Pancreatic lipase extracted from pigs. Enteric-coated capsules.