Transcript
Pharmacology of the GIT system
2005
LECTURE Outline
• REVIEW the Anatomy of the GIT
• REVIEW the Physiology of the GIT
• Review common GI drugs in the following categories:– 1. Drugs affecting GI secretions– 2. Laxatives– 3. Anti-diarrheals– 4. Emetics and anti-emetics
Fig. 16.1
Fig. 16.10a
Fig. 16.10b
Fig. 16.11a
Fig. 16.11b
Fig. 16.12
Drugs affecting GI secretions
There are five types of drugs that affect gastric acid secretions and are useful for the treatment of peptic ulcer.
1. Histamine (H2) receptor antagonist/blockers
2. Antacids
3. Proton pump inhibitors
4. Mucosal protectants
5. Prostaglandin analogs
Drugs affecting secretions: anti ulcer
Anti-ulcer drugs Prototype
Histamine (H2) receptor antagonist/blockers
Cimetidine
Antacids AlOH and MgOH
Proton pump inhibitors Omeprazole
Mucosal protectants Sucralfate
Prostaglandin analog Misoprostol
General indication of the drugs affecting gastric acid secretion
• Peptic ulcer
• Gastritis
• Patient on NPO to prevent stress ulcer
General time of administration of the drugs affecting gastric acid secretion
Anti-ulcer drugs Prototype Best time to give
Histamine (H2) receptor antagonist/blockers
Cimetidine With FOOD or ONE
hour after ANTACID
Antacids AlOH and MgOH Usually after meals
Proton pump inhibitors
Omeprazole BEFORE MEALS
Mucosal protectants
Sucralfate BEFORE MEALS
Prostaglandin analog
Misoprostol WITH MEALS
Pharmacodynamics
Histamine (H2) receptor blockers
• These drugs BLOCK the release of hydrochloric acid in the stomach in response to gastrin
Drugs affecting GI secretions
Antacids
• These drugs interact with the gastric acids at the chemical level to neutralize them
Drugs affecting GI secretions
Proton pump inhibitors
• These drugs suppress the secretion of hydrochloric acid into the lumen of the stomach
Drugs affecting GI secretions
Mucosal protectants
• These are agents that coat any injured area in the stomach to prevent further injury from acid
Drugs affecting GI secretions
Prostaglandin analogs
• These are agents that inhibit the secretion of gastrin and
• increase the secretion of mucus lining of the stomach, providing a buffer.
The H2 Blockers- “tidines”
Prototype: Cimetidine
• 1. Ranitidine
• 2. Famotidine
• 3. Nizatidine
The H2 Blockers- “tidines”
Pharmacodynamics: Drug Action• The H2 blockers are antagonists at the
receptors in the parietal cells of the stomach.
• The blockage results to inhibition of the hormone gastrin.
• There will be decreased production of gastric acid from the parietal cells.
• Also, the chief cells will secrete less pepsinogen.
The H2 Blockers- “tidines”Therapeutic use of the H2 blockers• Short-term treatment of active duodenal
ulcer or benign gastric ulcer• Treatment of hypersecretory conditions like
the Zollinger-Ellison syndrome• Prevention of stress-induced ulcers and
acute GI bleeding• Treatment of erosive GERD (reflux disease)• Relief of Symptoms of heart burn and acid
indigestion
The H2 Blockers- “tidines”
Precautions and Contraindications• Any known allergy is a clear
contraindication to the use of the agents. • Conditions such as pregnancy, lactation,
renal dysfunction and hepatic dysfunction should warrant cautious use.
• Nizatidine can be used in hepatic dysfunction.
The H2 Blockers- “tidines”
Dynamics- Side effects/adverse effects
• GIT= diarrhea or constipation
• CNS= Dizziness, headache, drowsiness, confusion and hallucinations
• Cardio= arrhythmias, HYPOTENSION (related to H2 receptor blockage in the heart)
• Cimetidine= Gynecomastia and impotence in males
The H2 Blockers- “tidines”
Drug-drug Interactions• Cimetidine, Famotidine, Ranitidine
are metabolized in the liver- they can cause slowing of excretion of other drugs leading to their increased concentration.
The H2 Blockers- “tidines”
Drug-drug Interactions
These drugs can interact with CIMETIDINE
• Anticoagulants
• Phenytoin,
• Alcohol
• Antidepressants.
The H2 Blockers- “tidines”Nursing considerations:• Administer the drug WITH meals at
BEDTIME to ensure therapeutic level• One hour after Antacids• Stress the importance of the
continued use for the length of time prescribed
The H2 Blockers- “tidines”Nursing considerations• Monitor the cardiovascular status
especially if the drugs are given IV• Warn patient of the potential problems
of increased drug concentration if the H2 blockers are used with other drugs or OTC drugs. Advise consultation first!
The H2 Blockers- “tidines”
Nursing considerations:
• Provide comfort measures like analgesics for headache, assistance with ambulation and safety measures because of confusion
• Warn the patients taking cimetidine that drowsiness may pose a hazard if driving or operating delicate machines.
The H2 Blockers- “tidines”
Nursing considerations:
• Provide health teaching as to the dose, frequency, comfort measures to initiate when side-effects are intolerable
Evaluate the effectiveness
• Relief of symptoms of ulcer, heart burn and GERD
The Antacids
These are drugs or inorganic chemicals that have been used for years to neutralize acid in the stomach
The Antacids
The following are the common antacids that can be bought OTC:
• Aluminum salts (hydroxide)
• Calcium salts (carbonate)
• Magnesium salts (milk of magnesia)
• Sodium bicarbonate
• Magaldrate (aluminum and magnesium combination)
The Antacids
Pharmacodynamics: drug action
• These agents act to neutralize the acidic pH in the stomach.
• They do not affect the rate of gastric acid secretion.
The Antacids
Pharmacodynamics: drug action
• The administration of antacid may cause an acid rebound.
• Neutralizing the stomach content to an alkaline level stimulates gastrin production to cause an increase in acid production and return the stomach to its normal acidic state.
The Antacids
Therapeutic Indications
• Symptomatic relief of upset stomach associated with hyperacidity
• Hyperacidic conditions like peptic ulcer, gastritis, esophagitis and hiatal hernia
• Special use of AMPHOGEL (aluminum hydroxide): to BIND phosphate
The Antacids
Precautions of Antacid Use• Known allergy is a clear
contraindication• Caution should be instituted if used in
electrolyte imbalances, GI obstruction and renal dysfunction.
• Sodium bicarbonate is rarely used because of potential systemic absorption metabolic alkalosis!!!
The Antacids
Pharmacokinetics
• These agents are taken orally and act locally in the stomach
The AntacidsPharmacodynamics: Effects of drugs1. GIT= rebound acidity; alkalosis may
occur.• Calcium salts may lead to hypercalcemia • Magnesium salts can cause DIARRHEA• Aluminum salts may cause
CONSTIPATION and Hypophosphatemia by binding with phosphates in the GIT.
2. Fluid retention due to the high sodium content of the antacids.
The AntacidsNursing Considerations:• Administer the antacids apart from any
other medications by ONE hour before or TWO hours after- to ensure adequate absorption of the other medications
• Tell the patient to CHEW the tablet thoroughly before swallowing. Follow it with one glass of water
• Regularly monitor for manifestations of acid-base imbalances as well as electrolyte imbalances
The Antacids
Nursing Considerations:• Provide comfort measures to alleviate
constipation associated with aluminum and diarrhea associated with magnesium salts.
• Monitor for the side-effects, effectiveness of the comfort measures, patient’s response to the medication and the effectiveness of the health teachings
The Antacids
Nursing Considerations
Evaluate for effectiveness:
Decreased symptoms of ulcer and pyrosis
Decreased Phosphate level (Amphogel) in patients with chronic renal failure
The PPI
These are the newer agents for ulcer treatment
• The “prazoles”
Prototype: Omeprazole
• Lanisoprazole
• Esomeprazole
• Pantoprazole
The PPIPharmacodynamics: drug action
• They act at specific secretory surface receptors to prevent the final step of acid production and thus decrease the level of acid in the stomach.
• The “pump” in the parietal cell is the H-K ATPase enzyme system on the secretory surface of the gastric parietal cells
The PPIClinical use of the PPIs
• Short-term treatment of active duodenal ulcers, GERD, erosive esophagitis and benign gastric ulcer
• Long-term- maintenance therapy for healing of erosive disorders.
The PPIPrecautions with the use of the PPIs
• Known allergy is a clear contraindication
• Caution if patient is pregnant
The PPIPharmacodynamics: Adverse effects
• CNS- dizziness, headache, asthenia (loss of strength), vertigo, insomnia, apathy
• GIT- diarrhea, abdominal pain, nausea, vomiting, dry mouth and tongue atrophy
• Respi- cough, stuffy nose, hoarseness and epistaxis.
The PPI
Nursing considerations:• Administer the drug BEFORE meals.
Ensure that patient does not open, chew or crush the drug.
• Provide safety measures if CNS dysfunction happens.
• Arrange for a medical follow-up if symptoms are NOT resolved after 4-8 weeks of therapy.
The PPI
Nursing considerations:
• Provide health teaching as to drug name, dosages and frequency, safety measures to handle common problems.
• Monitor patient response to the drug, the effectiveness of the teaching plan and the measures to employ
The PPI
Nursing considerations:
Evaluate for effectiveness of the drug
• Healing of peptic ulcer
• Decreased symptoms of ulcer
The Mucosal Protectant
Sucralfate (Caralfate/ Iselpin)
• This is given to protect the eroded ulcer sites in the GIT from further damage by acid and digestive enzymes
Sucralfate
Pharmacodynamics: Action of drug
• It forms an ulcer-adherent complex at duodenal ulcer sites, protecting the sites against acid, pepsin and bile.
• This action prevents further breakdown of proteins in the area and promotes healing.
Sucralfate
Clinical use of sucralfate
• Short and long term management of duodenal ulcer.
• NSAIDs induced gastritis
• Prevention of stress ulcer
• Treatment of oral and esophageal ulcers due to radiation, chemotherapy or sclerotherapy.
Sucralfate
Precautions on the use of Sucralfate
• This agent should NOT be given to any person with known allergy to the drug, and to those patients with renal failure/dialysis because of build-up of aluminum may occur if used with aluminum containing products.
The Mucosal Protectant
Pharmacodynamics: Side-effects & adverse reactions
• Primarily GIT= CONSTIPATION, occasionally diarrhea, nausea, indigestion, gastric discomfort, and dry mouth may also occur
• CNS= dizziness, drowsiness, vertigo
• Others= rash and back pain
The Mucosal Protectant
Drug-drug interactions
• If used with aluminum salts= high risk of accumulation of aluminum and toxicity.
• If used with phenytoin, fluoroquinolones and penicillamines- decreased levels of these drugs when taken with sucralfate
The Mucosal Protectant
Nursing Considerations• Administer drug ON AN EMPTY stomach, 1
hour before meals , or 2 hour after meals and at BEDTIME
• Monitor for side-effects like constipation and GI upset
• Encourage intake of high-fiber foods and increased fluid intake
• Administer antacids BETWEEN doses of sucralfate, NOT WITHIN 30 minutes of sucralfate dose
The Mucosal Protectant
Nursing Considerations• Provide comfort measures if CNS
effects occur• Provide health teaching as to drug
name, dosages and frequency, safety measures to handle common problems.
• Monitor patient response to the drug, the effectiveness of the teaching plan and the measures employed
The Mucosal Protectant
Nursing Considerations
• Evaluate effectiveness of therapy
Healing of ulcer
No formation of ulcer
Prostaglandin analogue
Misoprostol
• This agent is a synthetic prostaglandin E1 analog that is employed to protect the lining of the mucosa of the stomach
Prostaglandin analogue
Misoprostol: Pharmacodynamics
• Being a prostaglandin analog, it inhibits gastric acid secretion to some degree
• It INCREASES mucus production in the stomach lining.
Prostaglandin analogue
Misoprostol: Clinical use
• NSAIDs-induced gastric ulcers
• Duodenal ulcers unresponsive to H2 antagonists
Prostaglandin analogue
Precautions of Misoprostol Use• This drug is CONTRAINDICATED during
pregnancy because it is an abortifacient.• Women should be advised to have a negative negative
pregnancy test within 2 weeks of beginning pregnancy test within 2 weeks of beginning therapy and should begin the drug on the therapy and should begin the drug on the second or third day of the next menstrual second or third day of the next menstrual cycle.cycle.
• They should be instructed in the use of contraceptives during therapy.
Prostaglandin analogue
Pharmacodynamic effects: drug reactions
• GIT= Nausea, diarrhea, abdominal pain, flatulence, vomiting, dyspepsia
• GU effects= miscarriages, excessive uterine CRAMPING and bleeding, spotting, hyper-menorrhea and menstrual disorders.
Prostaglandin analogueNursing Considerations• Administer to patients at risk for NSAIDs-induced
ulcers during the full course of NSAIDs therapy• Administer four times daily with meals and at
bedtime• Obtain pregnancy test within 2 weeks of
beginning therapy. • Begin the therapy on second or third day of
menstrual period to ensure that the woman is not pregnant
Prostaglandin analogue
Nursing Considerations• Provide patient with both written and oral
information regarding the associated risks of pregnancy
• Provide health teaching as to drug name, dosages and frequency, safety measures to handle common problems.
• Monitor patient response to the drug, the effectiveness of the teaching plan and the measures to employ
Laxatives
• Generally used to INCREASE the passage of the colonic contents
• The general classifications is as follows:
1. Chemical stimulants- irritants
2. Mechanical stimulants- hyperosmotic agents and saline cathartics
3. Lubricants and stool softeners
Laxatives
• They promote bowel evacuation for various purposes
• They are classified into their mode of action
Laxatives
Type Prototype Action
Chemical stimulants
Bisacodyl (Dulcolax)
Direct stimulation of the GIT nerves
Irritant laxatives
Mechanical (bulk) stimulants
Lactulose Increased fluid content of the fecal material causing stimulation of the local reflex
Lubricants Docusate
Mineral oil
Lubricating the intestinal material to promote passage through the GIT
Therapeutic Indications of the Laxatives
• SHORT term relief of ConstipationConstipation
• Prevention of strainingPrevention of straining in conditions like CHF, post-MI, post partum, post-op
• Preparation for diagnostic examinationdiagnostic examination
• Removal of poison or toxins
• Adjunct in anti-helminthic therapy
• To remove AMMONIA by use of lactulose
Contraindications in Laxative use
• ACUTE abdominal disorders
–AppendicitisAppendicitis
–DiverticulitisDiverticulitis
–Ulcerative colitisUlcerative colitis
Chemical Stimulant Cathartics
Prototype: Bisacodyl
Irritant laxatives:
• 1. Castor oil
• 2. Senna
• 3. Cascara
• 4. Phenolphthalein
Chemical Stimulant Cathartics
Pharmacodynamics
• These agents DIRECTLY stimulate the nerve plexus in the intestinal wall
• The result is INCREASED movement or motility of the colon
Mechanical Stimulant Cathartics
Prototype: LACTULOSE (Cephulac)
Bulk-forming laxatives
• 1. Magnesium (citrate, hydroxide, sulfate)- saline cathatic
• 2. Psyllium
• 3. Polycarbophil
Mechanical Stimulant Cathartics
Pharmacodynamics
• These agents are rapid-acting laxatives that INCREASE the GI motility by– Increasing the fluids in the colonic
material– Stimulating the local stretch receptors– Activating local defection reflex
Lubricants-Stool softener
Prototype: Docusate
• 1. Glycerin
• 2. Mineral oil
Lubricants-stool softeners
Pharmacodynamics
• Docusate increases the admixture of fat and water producing a softer stool
• Glycerin and Mineral oil form a slippery coat on the colonic contents
Pharmacokinetics: Common Side-effects of the Laxatives
• Diarrhea
• Abdominal cramping
• Nausea
• Fluid and electrolyte imbalance
• Sympathetic reactions- sweating, palpitations, flushing and fainting
• CATHARTIC dependence
The Nursing Process and Laxative
ASSESSMENT
• Nursing History- elicit allergy to any laxatives, elicit history of conditions like diverticulitis and ulcerative colitis
• Physical Examination- abdominal assessment
• Laboratory Test: fecalysis, electrolyte levels
The Nursing Process and Laxative
NURSING DIAGNOSIS
• Alteration in bowel pattern
• Alteration in comfort: pain
• Knowledge deficit
The Nursing Process and Laxative
IMPLEMENTATION
1. Emphasize that it is use on a SHORT term basis
2. Provide comfort and safety measures like ready access to the bathroom, side-rails
3. Administer with a full glass of water
The Nursing Process and Laxative
IMPLEMENTATION
4. Encourage fluid intake, high fiber diet and daily exercise
5. DO NOT administer if acute abdominal condition like appendicitis is present
6. Advise to change position slowly and avoid hazardous activities because of potential dizziness
The Nursing Process and Laxative
IMPLEMENTATION7. Record intake and output to assess
fluid alteration8. If possible, observe the character of
stools9. Caution the patient that chronic use
may promote dependence and use during pregnancy may cause uterine cramping and Vitamin deficiency
The Nursing Process and Laxative
EVALUATION of drug effectiveness
1. Evaluate relief of GI symptoms, absence of staining and increased evacuation of GI tract
2. For Lactulose: decreased ammonia
3. Nomal bowel fucntion is restored
The Anti-diarrheals
• These are agents used to calm the irritation of the GIT for the symptomatic relief of diarrhea
• General Classifications
1. Local anti-motility
2. Local reflex inhibition
3. Central action on the CNS
The Anti-diarrhealsType Prototype Action
Local reflex inhibitor
Bismuth subsalicylate
Locally coats the lining of the GIT to soothe irritation
Local anti-motility
Loperamide Directly inhibits the intestinal muscle activity to SLOW peristalsis
Central acting agent
Opium derivatives (paregoric)
Stops GIT spasm by CNS action
Clinical Indications of drug use
• Relief of symptoms of acute and chronic diarrhea
• Reduction of fecal volume discharges from ileostomies
• Prevention and treatment of traveler's diarrhea
Contraindications of anti-diarrheal Use
• Poisoning
• Drug allergy
• GI obstruction
• Acute abdominal conditions
Pharmacokinetics: Side effects
• Constipation
• Nausea, vomiting
• Abdominal distention and discomfort
• TOXIC MEGACOLON
Nursing process and anti-diarrheals
ASSESSMENT
• Nursing History – Elicit history of drug allergy, conditions like poisoning, GI obstruction and acute abdominal conditions
• Physical Examination- Abdominal examination
• Laboratory test- electrolyte levels
Nursing process and anti-diarrheals
NURSING DIAGNOSIS
• Alteration in bowel pattern
• Alteration in comfort: pain
Nursing process and anti-diarrheals
IMPLEMENTATION
1. Monitor patient response within 48 hours. Discontinue drug use if no effect
2. Provide comfort measures for pain
3. Provide teaching regarding its short term use only
Nursing process and anti-diarrheals
EVALUATION
1. Monitor effectiveness of drug- RELIEF of diarrhea
2. Monitor adverse effects, effectiveness of pain measures and effectiveness of teaching plan
Emetics and Anti-emetics
Emetic Agent• Syrup of Ipecac
Anti-emetics• 1. Phenothiazines• 2. Non-phenothiazines• 3. Anticholinergics/Antihistamines• 4. Serotonin receptor Blockers• 5. Miscellaneous
EMETIC
• Prototype: Ipecac Syrup
EMETIC
Pharmacodynamics
• Ipecac syrup irritates the GI mucosa locally, resulting to stimulation of the vomiting center
• It acts within 20 minutes
EMETIC
Clinical Use of ipecac
• To induce vomiting as a treatment for drug overdose and certain poisonings
EMETIC
Contraindications of Ipecac use
• Ingestion of CORROSIVE chemicals
• Ingestion of petroleum products
• Unconscious and convulsing patient
EMETIC
Pharmacokinetics: side effects of Ipecac
• Nausea
• Diarrhea
• GI upset
• Mild CNS depression
• CARDIOTOXICITY if large amounts are absorbed in the body
Nursing process and the EMETIC
ASSESSMENT
• Nursing History- elicit the exact nature of poisoning
• Physical Examination- CNS status and abdominal exam
Nursing process and the EMETIC
IMPLEMENTATION1. Administer to conscious patient only2. Administer ipecac as soon as
possible3. Administer with a large amount of
water4. Vomiting should occur within 20
minutes of the first dose. Repeat the dose and expect vomiting to occur with 20 minutes
Nursing process and the EMETIC
IMPLEMENTATION
5. Provide comfort measures like ready access to bathroom, assistance with ambulation
6. Offer support
Nursing process and the EMETIC
EVALUATION
1. Evaluate patient response within 20 minutes of drug ingestion
2. Monitor for adverse effects
3. Evaluate effectiveness of comfort measures and teaching plan
ANTI-EMETICS
• These are agents used to manage nausea and vomiting
• They act either locally or centrally• In general, they may inhibit the
chemoreceptor trigger zone in the medulla by blocking DOPAMINE receptor
• Others act by decreasing the sensitivity of the vestibular apparatus
ANTIEMETICS
Anti-emetic types Common examples
Phenothiazines Prochlorperazine, Promethazine
Non-phenothiazines Metoclopramide
Anticholinergics and Antihistaminics
Meclizine, buclizine
Serotonin Receptor blockers
“setron”- dolasetron
Miscellaneous Dronabinol, hydroxyzine
ANTIEMETICSTypes Pharmacodynamics
Phenothiazines Centrally block the vomiting center in the medulla
Non-phenothiazine Reduces the responsiveness of the nerve cell in the medulla; also blocks the dopamine receptors
Anticholinergics Block the transmission of the impulses to the medulla
Serotonin receptor blockers
Centrally and locally inhibits the serotonin receptors
Miscellaneous Act in the CNS , either in the medulla or in the cortex
ANTIEMETICSTypes Clinical Use
Phenothiazines N/V associated with anesthesia, intractable hiccups
Non-phenothiazine N/V associated with chemical stimulation
Anticholinergics N/V associated with motion sickness
Serotonin-receptor Blockers
N/V associated with chemotherapy
Miscellaneous N/V associated with chemotherapy
ANTIEMETICS
Indications
• 1. Prevention and treatment of vomiting
• 2. Motion sickness
ANTIEMETICS
Contraindications
• 1. Severe CNS depression
• 2. Severe liver dysfunction
ANTIEMETICS
Pharmacokinetics:
• Oral absorption is good if vomiting is not present
• IV drugs can be given if vomiting is active
• Most drugs are metabolized in the liver excreted in the kidneys
ANTIEMETICS
Pharmacokinetics: Side-effects1. PHOTHOSENSITIVITY2. Drowsiness, dizziness, weakness and
tremors and DEHYDRATON3. Phenothiazines= autonomic anti-
cholinergic effects like dry mouth, nasal congestion and urinary retention
Metoclopramide= EPS due to dopamine receptor blockage
Nursing Process and the ANTIEMETICS
ASSESSMENT
• Nursing History- elicit allergy, impaired hepatic function and CNS depression
• Physical Examination- CNS status and abdominal examination
• Laboratory test- Liver function studies
Nursing Process and the ANTIEMETICS
NURSING DIAGNOSIS
1. Alteration in comfort: pain
2. High risk for injury
3. Knowledge deficit
Nursing Process and the ANTIEMETICS
IMPLEMENTATION
1. Assess patient’s intake of other drugs that may cause dangerous drug interaction
2. Emphasize that this is given on a short term basis
Nursing Process and the ANTIEMETICS
IMPLEMENTATION
3. Provide comfort and safety measures– Advise to change position slowly– Avoid hazardous activities– Provide mouth care and ice chips– Monitor for dehydration and offer fluids if
it occurs
Nursing Process and the ANTIEMETICS
IMPLEMENTATION
4. Protect from sun exposure– Sunscreens – Protective covering
5. Provide health teaching
Nursing Process and the ANTIEMETICS
EVALUATION
1. Monitor for the drug effectiveness• Relief of nausea and vomiting
2. Monitor for adverse effects
3. Evaluate effectiveness of comfort measures and teaching plan
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