lower GI pharmacology Flashcards
anti-emetics for cancer chemo
Class I: PRN- lorazepam, prochlorperazine + diphenhydramine, metoclopramide + diphenhydramine. class II: dexamethasone. Class III: ondansetron + Dex. Class IV: Granisetron + Dex. Class V: granisetron + Dex
anti-emetics for pregnancy
First line: pyridoxine (B6) + doxylamine (H1 antagonist). If persists: add diphenhydramine or meclizine. Then: proclorperazine (D2 antagonist) or metoclopramide. If dehydration requiring hospitalization: ondansetron. If refractory n/v (2nd trimester): methylprednisone
list 5HT3 receptor antagonists
Ondansetron
5HT3 antagonists uses
prevent chemotherapy induced n/v, post-op emesis, N/V associated with post-op opioids
list Dopamine (D2) receptor antagonists
Prochloroperazine , Metoclopramide (also blocks 5HT3)
dopamine antagonist side effects
Extrapyramidal symptoms (movement disorders)
dopamine antagonist uses
Metoclopramide used for n/v of chemotherapy. Prochlorperazine less effective against emetic stimuli in gut (mediated via 5HT3 receptors). But also blocking M and H1 receptors increases their utility in nausea with motion sickness
List Antihistamines (1st generation)
Meclizine, promethazine, Diphenhydramine (dimenhydrinate)
antihistamine uses
motion sickness and postoperative emesis
list Anticholinergic agents
Scopolamine
Anticholinergic agents uses
Primarily prevention/treatment of motion sickness. Also post operative n/v
Anticholinergic agents pharmacokinetics
transdermal- duration of action 72 hrs
Which drugs can induce constipation
antimuscarinics, drugs with antimuscarinic side effects (antihistamines, TCAs, antipsychotics), antacids, Ca channel blockers (verapimil), opioids, 5HT3 antagonists
List Bulk-forming / fiber laxatives
Psyllium Seed (metamucil)
Fiber uses and MOA
first line agent for constipation. Approximates physiological mechanism (facilitates passage-stimulates peristalsis via H20 absorption > bulk expansion)
Fiber pharmacokinetics
•Effective in 12-24 hrs to 3 days - take with fluids. May combine and interact with other drugs (digoxin / salicylates), so space dosing
List Saline (osmotically-active) cathartics
Mg(OH)2, Polyethylene glycols, lactulose
Saline (osmotically-active) cathartics uses
Added to fiber as second line/step for constipation.Mg(OH)2 used for mild/moderate constipation. Polyethylene glycol used for bowel cleansing before medical procedures (high volume) or difficult constipation (low volume). lactulose: used in elderly Also used in purging doses for food/drug poisoning
Saline (osmotically-active) cathartics MOA
Non-absorbable ions > osmotic retention of intestinal water > increased peristalsis
Saline (osmotically-active) cathartics pharmacokinetics
Mg(OH2): avoid in renal dysfunction. Can lead to electrolyte imbalance. PEG: high volume has electrolyts added to prevent net transfer but low volume solns may lead to electrolyte depletion.
List Stimulant / irritant laxatives
Bisacodyl (dulcolax)
Stimulant / irritant laxatives uses
used for constipation if fiber/saline fails.
Bisacodyl MOA
increases peristaltic activity via local irritation > accumulation of water and electrolytes > increased motility
Bisacodyl side effects
electrolyte / fluid deficiencies, severe cramping
List Wetting agents / emollient laxatives
Docusate (ex lax extra gentle)
Ducosate MOA
surfactant that acts as stool-softener (facilitates admixture of aqueous and fatty substances)
Ducosate uses
primary prevention in pts with CV dz, hernia, post partum
List meds used for opioid induced constipation
Managed with stool softeners (docusate), stimulant laxatives (bisacodyl - senna), osmotic laxatives (PEG [Miralax®] - milk of magnesia)
two causes of diarrhea
decreased absorption of fluid/electrolytes (osmotic) or increased secretion of fluid and electrolyes
Causes of osmotic diarrhea
Carbohydrate malabsorption (lactose, sorbitol, fructose) , osmotic laxatives (magnesium, colonoscopy preps)
causes of secretory diarrhea
bacteria (cholera, e.coli), neuroendocrine tumors, ileal bile salt malabsorption, stimulant laxatives, disordered motility (diabetic neuropathy, IBS)
drugs that can induce diarrhea
antibiotics, colchicine (anti inflammatory for gout), digoxin, misoprostol (prostaglandin anolog), muscarinic agents, reserpine, SSRIs
Which antibiotics are given for C. difficile, cholera and e.coli?
c. diff: metronidazole, vancomycin, rifaximin. Cholera: doxycycline, tetracycline or macrolide. E. coli: none
List antidiarrheal Opioids
Loperamide
opioids MOA
•Opioid receptor agonist affecting intestinal motility (m), intestinal secretion (d), and absorption (m and d)
opioids uses
Anti-secretory activity against cholera toxin. Effective against traveler’s diarrhea, alone or with antibiotics - discontinue if no improvement in 48 hours
opioid side effects
low addiction (low solubility), overdose can cause CNS depression and paralytic ileus
Polycarbophil MOA
binds free fecal water
polycarbophil uses
•Useful in diarrhea (absorbs 60X weight in H2O) and constipation (prevents fecal desiccation)
List Absorbent Agents
Bismuth, Kaolin / Pectin
absorbent agent uses
manages mild/moderate diarrhea by adsorbing toxins that cause irritation.
absorbent agents side effects
•Avoid use of bismuth subsalicylate in children under 12 y/o (salicylate risk for Reye’s syndrome)
List Drugs for IBS
Tegaserod (for constipation), Alosetron (for diarrhea)
Alosetron MOA
seretonin 5Ht3 antagonist- Block of 5-HT3 receptors on sensory and motor neurons reduces pain and inhibits colonic motility
alosetron uses
Severe IBS in women with diarrhea as the prominent symptom - restricted use due to risk of ischemic colitis
Tegaserod MOA
Serotonin 5-HT4 Agonist > release of NTs > peristaltic reflex > gastric empyting and intestinal motility
Tegaserod uses
IBS patients with predominant constipation
tegaserod side effects
•heart attacks, strokes, and unstable angina leading to restricted use
