Palliation of Constipation & Nausea/Vomiting Flashcards
Fecal Impaction
Fecal impaction is a mass of dry, hard stool that will not pass out of the colon or rectum. Fecal impaction is dry stool that cannot pass out of the body.
What are some bulk laxatives?
- Dietary fiber
* Psyllium
Bulk Laxatives MOA
○ Bulk-forming laxatives cause retention of fluid and an increase in fecal mass, resulting in stimulation of peristalsis.
○ They usually have an effect within 12 to 24 hours and reach a maximum after several days
Bulk Laxatives SE
Flatulence
Bulk Laxatives Contraindications
In debilitated patients who cannot drink adequate fluid (1.5 – 2 liters/day) could result in fecal impaction, intestinal obstruction
What are some osmotic laxatives?
- Nonabsorbable sugars
- Saline and Mg
- Polyethylene Glycol
Lactulose and Sorbitol MOA
Bacteria in the colon degrade the sugar and the increase in osmotic pressure and acidification of intestinal contents which in turn, softens the stool by promoting stool water content.
Lactulose and Sorbitol SE
○ Bloating, cramps, flatulence
○ Very sweet – may be difficult for patients to tolerate
○ Dehydration
MOA of:
○ Magnesium citrate
○ Magnesium hydroxide (Milk of Magnesia)
○ Sodium Phosphate (Fleets Phospho-Soda)
○ Saline laxatives have an osmotic effect causing increased intraluminal volume that acts as a stimulus for intestinal motility.
○ Laxatives that contain magnesium have been shown to release cholecystokinin that causes intraluminal accumulation of fluid and electrolytes and promotes
Mg Salt Laxative SE
○ Can produce dehydration without adequate fluid replacement
Mg Salt Laxative Contraindications
- Bowel obstruction
- Renal failure
- CHF
- Liver failure
Mg Salt Laxative Indications
○ Magnesium citrate and sodium phosphate indicated for bowel cleansing in preparing patients for surgery or the colon for x-ray or endoscopy
○ Magnesium hydroxide is indicated for relief of constipation
Polyethylene Glycol MOA
Polyethylene glycol is an osmotic agent that causes retention of water in the stool resulting in a softer stool and more frequent bowel movements.
Polyethylene Glycol SE
Minimal to none
Polyethylene Glycol Indications
o Large volume (ie 4 liters) ingested rapidly causes rapid evacuation for bowel cleansing before endoscopy
o Smaller daily doses can be used for constipation.
What are some stimulant laxatives?
- Senna
* Bisacodyl
Bisacodyl MOA
Bisacodyl is a contact laxative that acts on the large intestine to produce strong but brief peristaltic movements. This agent stimulates sensory nerve endings to produce parasympathetic reflexes that results in peristalsis of the colon. Local axon reflexes and segmental reflexes are stimulated, which produces widespread peristalsis of the colon.
Senna MOA
Senna undergoes conversion to active metabolites in the colon that stimulate the myenteric plexus and induce net fluid secretion.
Bisacodyl/Senna Indications
Constipation
Docusate MOA
Docusate is an anionic surfactant that is believed to stimulate intestinal secretion and increase the penetration of fluid into the stool by emulsifying feces, water, and fat
Docusate Indication
Docusate is used to soften or prevent the formation of hard stools.
Glycerin Suppository/Enema MOA
Due to its osmotic effect, glycerin softens, lubricates, and facilitates the elimination of inspissated feces. By serving as a bowel irritant it may also stimulate rectal contractions.
Mineral Oil Enema MOA
Mineral oil helps soften (by coating fecal material with mineral oil) and lubricate hard stools, easing their passage without irritating the mucosa.
Mineral Oil Enema Contraindications
Mineral oil should never be administered orally, particularly to debilitated patients - inhalation/aspiration of the oil can lead to lipoid pneumonitis.
Mineral Oil Enema/Glycerin Suppository Indications
Fecal Impaction
Sodium phosphate enema MOA
- Soften stool by increasing water content
- Distend distal colon inducing peristalsis
Sodium phosphate enema Indications
Fecal Impaction
What receptors trigger the Chemoreceptor Trigger Zone?
- Dopamine
- 5HT3 (serotonin)
What receptors trigger the vestibular apparatus?
- ACh
- Histamine
Prochlorperazine MOA
○ Prochlorperazine acts centrally by inhibiting the dopamine receptors in the medullary chemoreceptor trigger zone
○ It peripherally blocks the vagus nerve in the gastrointestinal tract
Prochlorperazine SE
Extrapyramidal effects, dystonic reactions - Parkinson’s like effects
Prochlorperazine Indications
○ Opioid related nausea and vomiting
○ Moderately effective for nausea caused by various
Metoclopramide MOA
○ Antiemetic properties are due to central and peripheral dopamine receptor inhibition
○ Within the gastrointestinal tract activation of dopamine receptors inhibits cholinergic smooth muscle stimulation; blockade of this effect is believed to be the primary prokinetic mechanism of action of metoclopramide.
Metoclopramide SE
- Extrapyramidal effects, such as dystonia, akathisia, parkinsonism, may develop due to central dopamine receptor blockade.
- Tardive dyskinesia
- CAREFUL in those with Parkinson’s
Metoclopramide Indications
○ Chemotherapy induced nausea and vomiting
○ Vomiting due to dysmotility of the upper GI tract - gastric stasis and diabetic gastroparesis
Ondansetron MOA
Ondansetron is a competitive, highly selective antagonist of 5- hydroxytryptamine (serotonin) subtype 3 (5-HT 3) receptors.
Ondansetron SE
- Most common side effect is headache
- Small but statistically significant prolongation of the QT interval
Ondansetron Indications
○ Chemotherapy induced nausea and vomiting and its prophylaxis
○ Radiation induced nausea and vomiting and its prophylaxis
Promethazine MOA
Antiemetic effects come from its H(1) histamine receptor blocking properties.
Promethazine SE
Sedation
Promethazine Indications
Promethazine is effective in the active and prophylactic treatment of motion sickness
Scopolamine MOA
Pure anticholinergic agent
Scopolamine SE
○ Dry mouth (xerostomia)
○ Acute narrow angle glaucoma
○ Urinary retention
○ Confusion
Scopolamine Indications
○ Treatment of motion sickness
Scopolamine Contraindications
Glaucoma
