GI Drugs

Bulk Forming Laxatives

Names: Methylcellulose (Citrucel), Psyllium (Metamucil), Polycarbophil (FiberCon)

MOA: Work in the small intestine and colon, absorb water, thereby softening and enlarging the fecal mass; fecal swelling promotes peristalsis.

Key Points:

• Produce Soft Stool in 1–3 days

• Administer bulk-forming laxatives with fluid to avoid esophageal obstruction

Surfactant Laxatives

Name: Docusate sodium (Colace), Docusate calcium

MOA: Work in the small intestine and colon, Surfactant action softens stool by facilitating penetration of water; it also causes secretion of water and electrolytes into the intestine.

Key Points: Produce Soft Stool in 1–3 days

Stimulant Laxatives

Name: Bisacodyl(Correctol, Dulcolax, Fleet Laxative), Senna (Senokot, Ex-Lax), Castor oil

MOA: Work in the small intestine and colon, (1) Stimulate peristalsis and (2) soften feces by increasing secretion of water and electrolytes into the intestine and decreasing water and electrolyte absorption.

Key Points:

• Produce Semifluid Stool in 6–12 hrs.

• stimulant laxatives are commonly misused (abused) by the public. To reduce abuse, educate patients about normal bowel function and about alternatives to laxatives

• taking senna [Senokot] for several days, can change urine color to yellowish-brown.

Osmotic Laxatives

Name: Magnesium hydroxide (Phillips’ Milk of Magnesia), Magnesium sulfate, Magnesium citrate, Sodium phosphate, Polyethylene glycol (GlycoLax, MiraLax, Peglax), Lactulose (Cephulac, Cholac), Lactitol (Pizensy)

MOA: Small intestine and colon. Osmotic action retains water and thereby softens the feces; fecal swelling promotes peristalsis.

Key Points:

• If high doses are given, produce watery stool in 2–6 hrs.

• must increase fluid intake to avoid dehydration

• Because of their relatively rapid onset, group I laxatives (castor oil, high-dose osmotic agents) should not be given at bedtime.

Peptic Ulcer: Antibiotics

Name: Amoxicillin, Bismuth [Pepto-Bismol], Clarithromycin [Biaxin], Metronidazole [Flagyl], Tetracycline, Tinidazole [Tindamax]

MOA: Eradicate Helicobacter pylori

Key Points: To avoid resistance and increase efficacy, at least two antibiotics should be used.

Peptic Ulcer: antisecretory agents: histamine2 receptor antagonists [H2RAs])

Name: Cimetidine [Tagamet], Famotidine [Pepcid]

MOA: Suppress acid secretion by blocking H2 receptors on parietal cells

Key Points: Cimetidine inhibits hepatic drug-metabolizing enzymes and can thereby cause levels of other drugs to rise. Don’t give same time as other meds

Peptic Ulcer: antisecretory agents: proton pump inhibitors [PPIs]

Name: Dexlansoprazole [Dexilant], Esomeprazole [Nexium], Lansoprazole [Prevacid], Omeprazole [Prilosec, Zegerid),

MOA: Suppress acid secretion by inhibiting H+, K+-ATPase, the enzyme that makes gastric acid

Key Points:

• PPIs are the most effective inhibitors of acid secretion.

• Although generally safe, PPIs can increase the risk of fractures, pneumonia, and hypomagnesemia and can cause acid rebound when treatment stops.

Peptic Ulcer: mucosal protectants

Name: Sucralfate [Carafate, Sulcrate)

MOA: Forms a barrier over the ulcer crater that protects against acid and pepsin

Key Points:

• minimal side effects and lack of significant drug interactions Do not give sucralfate with other meds , may reduce med absorption.

• Do not combine sucralfate with tube feedings

Peptic Ulcer: Antisecretory agents that enhance mucosal defenses

Name: Misoprostol [Cytotec]

MOA: Protects against NSAID-induced ulcers by stimulating secretion of mucus and bicarbonate, maintaining submucosal blood flow and suppressing secretion of gastric acid

Key Points: Misoprostol stimulates uterine contraction and hence is contraindicated during pregnancy.

Peptic Ulcer: Antacids

Name: Aluminum hydroxide, Calcium carbonate, Magnesium hydroxide

MOA: React with gastric acid to form neutral salts

Key Points:

• Most antacids affect the bowel →(e.g., aluminum hydroxide) promote constipation, magnesium hydroxide) promote diarrhea.

• Some antacid preparations contain substantial amounts of sodium

• Antacids can interfere with the actions of sucralfate and cimetidine To minimize this interaction, administer these drugs at least 1 hour apart.

Antiemetics: Serotonin Antagonists

Name: Ondansetron (Zofran, Zuplenz)

MOA: Block serotonin receptors on vagal afferents and in the Chemoreceptor trigger zone (CTZ)

Key Points: Chemotherapy, radiation, postoperative headache, diarrhea, dizziness

Antiemetics: Glucocorticoids

Name: Dexamethasone (Decadron), Methylprednisolone (Solu-Medrol)

MOA: unknown

Key Points: Chemotherapy

Antiemetics: Substance P/Neurokinin1 Antagonists

Name: Aprepitant (Emend)

MOA: Block receptors for substance P/neurokinin1 in the brain

Key Points: Chemotherapy

Antiemetics: Dopamine Antagonists

Name: Prochlorperazine

MOA: Block dopamine receptors in the CTZ

Key Points: Chemotherapy, postoperative, general

Antiemetics: Cannabinoids

Name: Dronabinol (Marinol)

MOA: unknown, but probably activate cannabinoid receptors associated with the vomiting center

Key Points: Chemotherapy

Antiemetics: Anticholinergics

Name: Scopolamine (Transderm Scōp)

MOA: Block muscarinic receptors in the pathway from the inner ear to the vomiting center

Key Points: Motion sickness

Antiemetics: Antihistamines

Name: Dimenhydrinate (generic only)

MOA: Block H1 receptors and muscarinic receptors in the pathway from the inner ear to the vomiting center

Key Points: Motion sickness

Three drugs are FDA approved for IBS

Alosetron, linaclotide, and Lubiprostone

Alosetron

• approved for IBS-D in women

• Benefits derive from blocking 5-HT3 receptors on neurons that innervate the viscera

• can cause ischemic colitis and severe constipation

IBS-C drugs

• Linaclotide: approved for adults. Constipation is treated through indirect stimulation of the secretion of chloride and bicarbonate into the intestinal lumen.

• Lubiprostone is approved for women. Benefits derive from activating (opening) chloride channels in the intestine.