NurseReview.Org - Pharmacology Git Drugs

Pharmacology of the GIT system

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.

Histamine (H2) receptor antagonist/blockers

Antacids

Proton pump inhibitors

Mucosal protectants

Prostaglandin analogs

Drugs affecting secretions: anti ulcer Misoprostol Prostaglandin analog Sucralfate Mucosal protectants Omeprazole Proton pump inhibitors AlOH and MgOH Antacids Cimetidine Histamine (H2) receptor antagonist/blockers Prototype Anti-ulcer drugs

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 Misoprostol WITH MEALS Prostaglandin analog Sucralfate BEFORE MEALS Mucosal protectants Omeprazole BEFORE MEALS Proton pump inhibitors AlOH and MgOH Usually after meals Antacids Cimetidine With FOOD or ONE hour after ANTACID Histamine (H2) receptor antagonist/blockers Prototype Best time to give Anti-ulcer drugs

Pharmacodynamics

Histamine (H2) receptor blockers

These drugs BLOCK the release of hydrochloric acid in the stomach in response to gastrin

Antacids

These drugs interact with the gastric acids at the chemical level to neutralize them

Proton pump inhibitors

These drugs suppress the secretion of hydrochloric acid into the lumen of the stomach

Mucosal protectants

These are agents that coat any injured area in the stomach to prevent further injury from acid

Prostaglandin analogs

These are agents that inhibit the secretion of gastrin and

increase the secretion of mucus lining of the stomach, providing a buffer.

Histamine 2 receptor blockers

The H2 Blockers- “tidines”

Prototype: Cimetidine

1. Ranitidine

2. Famotidine

3. Nizatidine

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.

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

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.

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

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 .

Drug-drug Interactions

These drugs can interact with CIMETIDINE

Anticoagulants

Phenytoin,

Alcohol

Antidepressants.

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

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!

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.

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

Antacids

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

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 Antacids

Pharmacodynamics: Effects of drugs

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 Antacids

Nursing 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

proton-pump inhibitors

The PPI

These are the newer agents for ulcer treatment

The “prazoles”

Prototype: Ome prazole

Laniso prazole

Esome prazole

Panto prazole

The PPI

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 PPI

Clinical 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 PPI

Precautions with the use of the PPIs

Known allergy is a clear contraindication

Caution if patient is pregnant

The PPI

Pharmacodynamics: 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

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

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

Evaluate for effectiveness of the drug

Healing of peptic ulcer

Decreased symptoms of ulcer

Mucosal protectants

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.

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

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

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

Provide comfort measures if CNS effects occur

Monitor patient response to the drug, the effectiveness of the teaching plan and the measures employed

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

Misoprostol: Pharmacodynamics

Being a prostaglandin analog, it inhibits gastric acid secretion to some degree

It INCREASES mucus production in the stomach lining.

Misoprostol: Clinical use

NSAIDs-induced gastric ulcers

Duodenal ulcers unresponsive to H2 antagonists

Precautions of Misoprostol Use

This drug is CONTRAINDICATED during pregnancy because it is an abortifacient.

Women should be advised to have a negative pregnancy test within 2 weeks of beginning therapy and should begin the drug on the second or third day of the next menstrual cycle.

They should be instructed in the use of contraceptives during therapy.

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.

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

Provide patient with both written and oral information regarding the associated risks of pregnancy

Monitor patient response to the drug, the effectiveness of the teaching plan and the measures to employ

laxatives

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 Lubricating the intestinal material to promote passage through the GIT Docusate Mineral oil Lubricants Increased fluid content of the fecal material causing stimulation of the local reflex Lactulose Mechanical (bulk) stimulants Direct stimulation of the GIT nerves Irritant laxatives Bisacodyl (Dulcolax) Chemical stimulants Action Prototype Type

Therapeutic Indications of the Laxatives

SHORT term relief of Constipation

Prevention of straining in conditions like CHF, post-MI, post partum, post-op

Preparation for diagnostic 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

Appendicitis

Diverticulitis

Ulcerative 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

NURSING DIAGNOSIS

Alteration in bowel pattern

Alteration in comfort: pain

Knowledge deficit

IMPLEMENTATION

Emphasize that it is use on a SHORT term basis

Provide comfort and safety measures like ready access to the bathroom, side-rails

Administer with a full glass of water

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

IMPLEMENTATION

7. Record intake and output to assess fluid alteration

8. If possible, observe the character of stools

9. Caution the patient that chronic use may promote dependence and use during pregnancy may cause uterine cramping and Vitamin deficiency

EVALUATION of drug effectiveness

Evaluate relief of GI symptoms, absence of staining and increased evacuation of GI tract

For Lactulose: decreased ammonia

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-diarrheals Stops GIT spasm by CNS action Opium derivatives (paregoric) Central acting agent Directly inhibits the intestinal muscle activity to SLOW peristalsis Loperamide Local anti-motility Locally coats the lining of the GIT to soothe irritation Bismuth subsalicylate Local reflex inhibitor Action Prototype Type

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 DIAGNOSIS

Alteration in bowel pattern

IMPLEMENTATION

Monitor patient response within 48 hours. Discontinue drug use if no effect

Provide comfort measures for pain

Provide teaching regarding its short term use only

EVALUATION

Monitor effectiveness of drug- RELIEF of diarrhea

Monitor adverse effects, effectiveness of pain measures and effectiveness of teaching plan

Emetic and anti-emetics

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

IMPLEMENTATION

Administer to conscious patient only

Administer ipecac as soon as possible

Administer with a large amount of water

Vomiting should occur within 20 minutes of the first dose . Repeat the dose and expect vomiting to occur with 20 minutes

IMPLEMENTATION

5. Provide comfort measures like ready access to bathroom, assistance with ambulation

6. Offer support

EVALUATION

Evaluate patient response within 20 minutes of drug ingestion

Monitor for adverse effects

Evaluate effectiveness of comfort measures and teaching plan

Anti-Emetics

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 Dronabinol, hydroxyzine Miscellaneous “ setron”- dolasetron Serotonin Receptor blockers Meclizine, buclizine Anticholinergics and Antihistaminics Metoclopramide Non-phenothiazines Prochlorperazine, Promethazine Phenothiazines Common examples Anti-emetic types

ANTIEMETICS Act in the CNS , either in the medulla or in the cortex Miscellaneous Centrally and locally inhibits the serotonin receptors Serotonin receptor blockers Block the transmission of the impulses to the medulla Anticholinergics Reduces the responsiveness of the nerve cell in the medulla; also blocks the dopamine receptors Non-phenothiazine Centrally block the vomiting center in the medulla Phenothiazines Pharmacodynamics Types

ANTIEMETICS N/V associated with chemotherapy Miscellaneous N/V associated with chemotherapy Serotonin-receptor Blockers N/V associated with motion sickness Anticholinergics N/V associated with chemical stimulation Non-phenothiazine N/V associated with anesthesia, intractable hiccups Phenothiazines Clinical Use Types

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-effects

1. PHOTHOSENSITIVITY

2. Drowsiness, dizziness, weakness and tremors and DEHYDRATON

3. 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 DIAGNOSIS

High risk for injury

Knowledge deficit

IMPLEMENTATION

Assess patient’s intake of other drugs that may cause dangerous drug interaction

Emphasize that this is given on a short term basis

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

IMPLEMENTATION

4. Protect from sun exposure

Sunscreens

Protective covering

5. Provide health teaching

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

End

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