Drugs Affecting the GI Flashcards Preview

Pharmacology Exam 2 > Drugs Affecting the GI > Flashcards

Flashcards in Drugs Affecting the GI Deck (50):
1

Peptic Ulcer Disease: Helicobacter Pylori

A major causative factor (60% of gastric and up to 90% of duodenal ulcers) is chronic inflammation due to Helicobacter pylori
H. pylori colonization increases gastrin secretion
Gastrin stimulates the production of gastric acid by parietal cells

2

Peptic Ulcer Disease: NSAIDs

Block the function of cyclooxygenase 1 (cox-1), which is essential for the production of prostaglandins (they cause pain, but necessary in the stomach).
The gastric mucosa protects itself from gastric acid with a layer of mucus, the secretion of which is stimulated by certain prostaglandins

3

GERD

incompetence of the lower esophageal sphincter
transient lower esophageal sphincter relaxation
hiatal hernia

Tendency of excessive and acidic stomach contents to back up, or reflux, into the lower and even upper esophagus

4

Antacids: Mechanism of Action

Increase gastric pH to neutralize stomach acid
Promote gastric mucosal defense mechanisms
They do this by stimulating the secretion of:
Mucus: protective barrier against HCl
Bicarbonate: helps buffer acidic properties of stomach
Antacids DO NOT prevent the overproduction of acid
Antacids neutralize the acid once it is in the stomach

5

Antacids: Drug Effects

Reduction of pain associated with acid-related disorders is the primary drug effect

Reducing acidity reduces pain

6

Antacids: Aluminum Salts

Have constipating effects
Often used with magnesium to counteract constipation
Often recommended for patients with renal disease (more easily excreted via the colon)

Examples
Aluminum carbonate: Basaljel
Hydroxide salt: AlternaGEL
Combination products (aluminum hydroxide and magnesium hydroxide): Maalox

7

Antacids: Magnesium Salts

Commonly cause diarrhea; usually used with other drugs to counteract this effect
Osmotic laxative
Dangerous when used with renal failure—the failing kidney cannot excrete extra magnesium, resulting in accumulation

Examples:
Combination products such as Maalox, Mylanta (aluminum and magnesium)
Hydroxide salt: magnesium hydroxide (MOM)

CRUCIAL: to have healthy kidneys

8

Antacids: Calcium Salts

Forms: many, but carbonate is most common
High acid-neutralizing capacity
May cause constipation, kidney stones, flatulence
Often advertised as an extra source of dietary calcium
More for prevention of GERD, upset stomach, not PUD

Example:
Tums (calcium carbonate)

9

Antacids: Sodium Bicarbonate

Highly acid-neutralizing capacity
Buffers the acidic properties of HCl
Quick onset, but short duration
May cause metabolic alkalosis
Sodium content may cause problems in patients with CHF, hypertension, or renal insufficiency (Not recommended for sodium-restricted diets

Examples:
Bicarbonate Salt: Alka-Seltzer

10

Antacids: Adverse Effects

Aluminum and calcium: Constipation
Magnesium: Diarrhea
Calcium Carbonate: Produces gas and belching; often combined with simethicone

11

Antacids: Drug Interactions

1.) Absorption of other drugs to antacids
Reduces the ability of the other drug to be absorbed into the body

2.) Chelation
Chemical binding, or inactivation, of another drug
Produces insoluble complexes
Result: reduced drug absorption

3.) Increased stomach pH
Increased absorption of basic drugs
Decreased absorption of acidic drugs

4.) Increased urinary pH
Increased excretion of acidic drugs
Decreased excretion of basic drugs

12

Antacids: Nursing Implications

Assess for allergies and pre-existing conditions that may restrict the use of antacids, such as:
Hypertension
Renal Disease
Electrolyte Imbalances
HF

Patients with HF or hypertension should not use antacids with high sodium content
Use with caution with other medications due to the many drug interactions
Take 2 hrs after other drugs, 1 hour after meals and at bedtime
Long-term self-medication with antacids may mask symptoms of serious underlying diseases, such as cancer or bleeding ulcers

13

H2 Antagonists

Block histamine at the (H2) receptors of acid-producing parietal cells
Production of hydrogen ions is reduced, resulting in decreased production of HCl

Suppressed acid secretion in the stomach

14

Histamine

Histamine is a substance that performs many functions:
It is involved in nerve impulse transmission, dilation of capillaries, contraction of smooth muscles, stimulation of gastric secretion, and acceleration of heart rate

Two types of histamine receptors
H1 (histamine1): mediate smooth muscle contractions and dilation of capillaries (causes vasodilation)
H2 (histamine2): mediates gastric acid secretion

15

H2 Antagonists: Adverse Effects

Cimetidine may induce impotence and gynecomastia
May also see:
Headaches, constipation, diarrhea, N/V, rash, other effects
Leukopenia, granulocytopenia, thrombocytopenia - rare
Confusion in elderly

16

H2 Antagonists: Drug Interactions

Cimetidine
Binds with P-450 microsomal oxidase system in the liver, resulting in inhibited oxidation of many drugs and increased drug levels

All H2 antagonists may inhibit the absorption of drugs that require an acidic GI environment for absorption (empty stomach)

SMOKING has shown to decrease the effectiveness of H2 blockers (causes hyperacidity of the stomach)

17

H2 Antagonists: Nursing Implications

Assess for allergies and impaired renal or liver function
Use with caution in patients who are confused, disoriented, or elderly (especially cimetidine)
For intravenous doses (famotidine), follow administration guidelines
Take 2 hours before or after antacids

18

Proton Pump Inhibitors

The parietal cells release positive hydrogen ions (protons) during HCl production
This process is called the “proton pump”
H2 blockers and antihistamines do not stop the action of this pump

Examples:
Total inhibition of gastric acid secretion
lansoprazole (Prevacid)
omeprazole (Prilosec)
rabeprazole (Aciphex)
pantoprazole (Protonix) (IV form available)
esomeprazole (Nexium)


-Prazole: proton pump inhibitors

19

Mechanism of Action of PPI’s

Irreversibly binds to H+/K+ ATPase enzyme system
This bond prevents the movement of hydrogen ions from the parietal cells into the stomach
Result: ALL gastric acid secretion is temporarily blocked
In order to return to normal acid secretion after PPI’s have been stopped, the parietal cell must synthesize new H+/K+ ATPase

20

Indications for PPI’s:

GERD maintenance therapy
Erosive esophagitis
Short-term treatment of active duodenal and benign gastric ulcers

Treatment of H. pylori–induced ulcers
Given usually with an antibiotic

21

Adverse Effects of PPI’s

Headache: H/A
Diarrhea
C-diff???

Pneumonia (aspiration: stomach is no longer acidic, bacteria colonizes)

22

Nursing Implications of PPI’s

Assess for allergies and history of liver disease
Extensively metabolized by p-450 system

*Pantoprazole (Protonix) is the only proton pump inhibitor available for parenteral administration, and can be used for patients who are unable to take oral medications

May increase serum levels of diazepam, phenytoin, and cause increased chance for bleeding with warfarin

PPIs often work best when taken 1 hour before meals

23

Sucralfate (Carafate)

*Cytoprotective drug and used for stress ulcers, PUD
medication that combats ulcers not by reducing gastric acid but by increasing mucosal protection

Attracted to and binds to the base of ulcers and erosions, forming a protective barrier over these areas, like a piece of gum

Protects these areas from pepsin, which normally breaks down proteins (making ulcers worse)

24

Sucralfate cont.d

Little absorption from the gut
Do not administer with other medications
May impair absorption of other drugs—give other drugs at least 1 hour before or after Sucralfate
Most common adverse effect: constipation
Binds with phosphate; may be used in chronic renal failure to reduce phosphate levels

25

Misoprostol (Cytotec)

Synthetic prostaglandin analog
Prostaglandins have cytoprotective activity
Protect gastric mucosa from injury by enhancing local production of mucus or bicarbonate
Promote local cell regeneration
Help to maintain mucosal blood flow
*Used for prevention of NSAID-induced gastric ulcers
Most common adverse effects: diarrhea, abdominal pain
*Pregnancy category X: causes premature labor

26

Prokinetic Agents

The prokinetic agents increase the effect of acetylcholine on the GI system.
Stimulates motility w/o stimulating GI secretion
Acetylcholine is responsible for normal GI function.
Prokinetic agents increase peristalsis and gastric emptying. Used for Diabetics to absorb/eliminate a meal.
Prototype drug: metoclopramide (Reglan).

27

Metoclopramide

Pharmacotherapeutics
Relieve symptoms of diabetic gastroparesis. Empties stomach.
Used IV to prevent N/V. Blocks dopamine/serotonin in brain associated with N/V
Assistance with gastric tube insertion, increase motility of tube - single dose

Pharmacodynamics
Mechanism of action is unclear
Appears to sensitize tissues to effect of acetylcholine
Increases peristalsis of Upper GI tract
Blocks CTZ receptors (dopamine/serotonin)—antiemetic effect

28

Metoclopramide cont.d

Contraindications and precautions
GI hemorrhage, perforation, or mechanical obstruction

Adverse effects
Restlessness, drowsiness, depression, insomnia, headache, anxiety, dizziness, and confusion

Drug interactions
Levodopa (Dopamine replacement for Parkinson’s), anticholinergics (works like acetylcholine), and narcotics
Used short term; movement issues like Parkinson’s if used long term (blocking dopamine)

Maximizing therapeutic effects
Give oral doses 30 minutes before each meal.
Do not administer metoclopramide concurrently with anticholinergic drugs.

Minimizing adverse effects
Monitor for evidence of depression.
Withhold the dose and notify the prescriber if Parkinson-like symptoms occur.

29

To promote the optimal effectiveness of the drug, metoclopramide should be given:

30 minutes before meals
Metoclopramide should be given 30 minutes before meals to achieve maximum effectiveness.

30

Antiemetics

Nausea and vomiting related to oncologic therapy is frequently difficult to manage.
Antiemetics, which suppress stimulation of the CTZ (Chemoreceptor Trigger Zone) are used to treat nausea and vomiting.

Antiemetic drugs are primarily from three main drug classifications—selective serotonin receptor antagonists, antidopaminergic drugs, and anticholinergic drugs.

Selective Serotonin Receptor Antagonists
Prevent the stimulation of type 3 serotonin receptors in the CTZ.
Prototype drug: ondansetron (Zofran)

31

Ondansetron

Pharmacotherapeutics
Prevent nausea and vomiting associated with cancer chemotherapy.

Pharmacokinetics
Metabolism: liver. Excreted: kidneys.

Pharmacodynamics
Blocks serotonin receptor sites in the CTZ , thus preventing nausea and vomiting.

Contraindications and precautions
Hypersensitivity

Adverse effects
Headache, constipation, and malaise

Drug interactions
Drugs metabolized by the cytochrome P-450 enzymes

32

Disorders Affecting Lower GI Tract

Flatus: Flatulence
Diarrhea
Constipation
Irritable bowel syndrome (IBS)
Inflammatory bowel disease (IBD): Crohn’s and Ulcerative Colitis

33

Antiflatulents

Used to relieve the painful symptoms associated with gas
Several drugs are used to bind or alter intestinal gas and are often added to antacid combination products
OTC antiflatulents
Simethicone: most common
Charcoal

34

Simethicone

Antiflatulent drug
Used to reduce the discomforts of gastric or intestinal gas (flatulence)
Alters surface tension of gas bubbles, forming larger bubbles that can be eliminated more easily
Result is decreased gas pain and increased expulsion via mouth or rectum

35

Antidiarrheal Mechanisms of Action: Adsorbents

Coat the walls of the GI tract
Bind to the causative bacteria or toxin, which is then eliminated through the stool
Examples: bismuth subsalicylate (Pepto-Bismol contains aspirin, Kaopectate), kaolin-pectin (Kaopectolin)

Constipation, dark stools
Hearing loss, tinnitus, metallic taste

36

Antimotility drugs: opiates

Decrease bowel motility and relieve rectal spasms
Decrease transit time through the bowel, allowing more time for water and electrolytes to be absorbed
Reduce pain by relief of rectal spasms

Examples: loperamide (OTC: Imodium), diphenoxylate HCl w/ atropine sulfate (Lomotil)

37

Adverse Effects of Antimotility drugs: opiates

Drowsiness, sedation, dizziness, lethargy
Nausea, vomiting, anorexia, constipation
*Respiratory depression
Bradycardia, palpitations, hypotension
Urinary retention
Flushing, rash, urticaria

38

Antidiarrheals: Interactions

Adsorbents cause increased bleeding time and bruising when given with anticoagulants

Adsorbents decrease the absorption of many drugs, including digoxin, clindamycin, quinidine, hypoglycemic drugs, others

39

Nursing Implications of Antidiarrheals

Obtain thorough history of bowel patterns, general state of health, and recent history of illness or dietary changes, and assess for allergies

*DO NOT give bismuth subsalicylate to children or teenagers with chickenpox or viral illness because of the risk of Reye’s syndrome (Seizure activity)

Assess fluid volume status, I&O, and mucous membranes before, during, and after initiation of treatment
Teach patients to notify their physician immediately if symptoms persist
Monitor for therapeutic effect

40

Constipation

Abnormally infrequent and difficult passage of feces through the lower GI tract
Symptom, not a disease
Disorder of movement through the colon and/or rectum
Can be caused by a variety of diseases
or drugs

41

Bulk-forming laxatives

Act similar to fiber found in diets (high fiber)
Ex: Psyillium (metamucil)

Absorb water to increase bulk
Ex: methylcellulose (Citrucel)

Distend bowel to initiate reflex bowel activity
Ex: polycarbophil (Fibercon)

42

Emollient

Stool softeners and lubricants
Promote more water and fat in the stools
Lubricate the fecal material and intestinal walls

Ex: Stool softeners: docusate salts (Colace, Surfak)
Lubricants: mineral oil

43

Hyperosmotic

Increased oncotic pressure in the colon draws water into the stool
Result: bowel distention, increased peristalsis, and evacuation

Ex: Lactulose (can be used as an enema, for hepatic issues metabolizing ammonia)
glycerin

44

Saline

Increase osmotic pressure within the intestinal tract, causing more water to enter the intestines
Result: bowel distention, increased peristalsis, and evacuation

Ex: magnesium sulfate (Epsom salts), Sodium phosphate (Fleet enema), Magnesium hydroxide (MOM), Magnesium citrate

45

Stimulant

Increases peristalsis via intestinal nerve stimulation
Ex: castor oil, cascarra, senna, bisacodyl

46

Bulk forming laxatives Adverse Effects

Impaction
Fluid overload? Pt should be taking high fluids with bulk-forming

47

Emollient Adverse Effects

Skin rashes
Decreased absorption of fat- soluble vitamins
Risk for bleeding if Vit K def.

48

Hyperosmotic Adverse Effects

Abdominal bloating
Rectal irritation

49

Saline Adverse Effects

Magnesium toxicity (with renal insufficiency)
Cramping
Electrolyte imbalances
Diarrhea
Increased thirst

50

Stimulant Adverse Effects

Nutrient malabsorption
Rectal irritation
Electrolyte imbalances
Gastric and rectal irritation