GI: Laxatives Flashcards
Intestinal fluid absorption
Majority of water uptake is in small intestine (duodenum, jejunum, ileum)
Causes of Constipation
- Lack of fiber
- Drugs: anticholinergics, opiates, iron, SSRIs, antiHTNs (nondihydropyridine CCBs – verapamil & diltiazem)
- Endocrine / metabolic
- Neurogenic d/o
- Organic causes
Management of Constipation
- ID & Tx underlying cause
- Nonpharm methods: increase dietary fiber, fluid, & exercise; respond to the urge to defecate
- Pharmacologic Tx: individualize
Pregnancy & Constipation: Mgmt
- 1st line: adequate dietary fiber & fluid intake, light physical activity, bulk forming laxative
- Other safe options: lactulose (chronulac), docusate (colace), polyethylene glycol (Miralax)
Agents to treat constipation
bulk forming laxatimes, stool surfactants, osmotic laxatives, stimulant laxatives
Types of bulk forming laxatives
Fiber: soluble and insoluble
Significance of fiber in constipation
FIber: Resists enzymatic digestion and reaches the colon unchanged
FIber: ADRs
Gas, bloating, impaction above colonic strictures
(bulk forming laxatives)
Fiber: dosing considerations
- Start at ½ or less the recommended dose to decrease gas and bloating
- Take w/8oz water: Risk of choking + help w/constipation
(bulk forming laxatives)
Fiber & colon cancer
Hx of colon cancer, don’t recommend fiber first line
Soluble fiber: agents
Wheat dextrin (Benefiber) QD
Psyllium (Metamucil) divided doses
Soluble fiber: MOA
- Undergoes fermentation via colonic bacteria resulting in: short chain FA production, increased bacterial mass
- absorbs water in the intestine to form a viscous liquid which promotes peristalsis and reduces transit time. UTD
Insoluble fiber: agents
- Methylcellulose (Citrucel): 3-6x/day
- Calcium Polycarbophil (Fibercon) 1-4x/day
Insoluble fiber: MOA
Unfermented fiber that attracts water and increases stool bulk
Stool surfactants: Agents
Docusate (Colace) *more common
Mineral oil
Stool Surfactants: MOA
Decreases stool surface tension
Softens stool allowing easier defecation
Docusate (Colace): Dosing
1-4 divided doses
(stool surfactants)
Docusate (Colace): ADRs
- Diarrhea
- Abdominal cramping
(stool surfactant)
Mineral oil: dosing
1-3 divided doses
Mineral Oil: ADRs
- Lipid pneumonitis w/aspiration
- Anal leakage
- Decreased fat soluble vitamin absorption (A,D,E,K)
- Diarrhea
Side effects are major limiting factor
(stool surfactants)
Osmotic Laxatives: Agents
Polyethylene glycol (MiraLax)
Magnesium containing
- Magnesium sulfate (Epsom salt)
- Magnesium hydroxide (Milk of magnesia)
- Magnesium citrate (Citroma)
Phosphate salts: Fleet Enema
Lactulose (Chronulac)
Osmotic Laxatives: MOA
Nonabsorbable agents that cause colonic osmotic water retention
Polyethylene glycol (MiraLax): ADRs
Bloating, cramping, flatulence, diarrhea
Polyethylene glycol (MiraLax): mixing agents
Mix powder w/water, juice, soda, tea
Polyethylene glycol (MiraLax): pregnancy & pedi
Safe in pregnancy
Pedi: >6mths
Osmotic laxatives: Magnesium containing agents
- Magnesium sulfate (Epsom salt)
- Magnesium hydroxide (Milk of magnesia)
- Magnesium citrate (Citroma)
Osmotic laxatives: Magnesium containing agents
ADRs
Abdominal pain, gas, N/V
Caution: renal insufficiency –> hypermagnesemia
Osmotic Laxatives: phosphate salts
Agents
Fleet enema
Phosphate salts: ADRs
Electrolyte abnormalities:
increased (PO4, Na), decreased (Ca, K)
(Osmotic laxatives)
Phosphate salts: caution in
elderly, renal insufficiency, cardiac dz
(Osmotic laxatives)
Oral Sodium Phosphate BBW
12/11/2008 FDA safety alert – assoc w/AKI and RF; OTC Fleet Phospho Soda removed from market, Rx products still available (Osmoprep)
(Osmotic laxatives)
Lactulose (Chronulac): MOA
Colonic bacteria hydrolyze short chain FAs –> osmotically draws water into the intestinal lumen
(Osmotic laxatives)
Lactulose (Chronulac): ADRs
Abdominal discomfort, flatulence, diarrhea
Stimulant laxatives: Agents
- Anthraquinone derivatives (Sennosides / Senekot)
- Diphenylmethane derivatives (Bisacodyl /Dulcolax)
Stimulant laxatives: MOA
Not well understood. Thought to have direct effects on:
Enterocytes, enteric neuron, GI smooth muscle
Induce limited low-grade inflammation –> water accumulation & peristalsis
Stimulant laxatives: PK
poorly absorbed, undergo colonic hydrolysis to active metabolites
Stimulant laxatives: ADRs
Cramps, nausea, rectal burning, vomiting
Anthraquinone derivatives (Sennosides / Senekot): Formulation & Dosing
Tablets, syrup, liquid
Daily, divided doses prn
(stimulant laxatives)
Anthraquinone derivatives (Sennosides / Senekot): ADRs
Stimulant laxative ADRs + melanosis coli (senna) – just color. goes away
Diphenylmethane derivatives (Bisacodyl / Dulcolax): Formulations and dosing
Rectal suppository, tablet
Once daily
(stimulant laxatives)
Assessment question: preferred for constipation w/opiates
rec’d combo of senna and dulcolax
Laxatives: Onset of action of 1-3 days
which laxatives & stool characteristics
Softened stool
- Bulk forming: *psyllium, methylcellulose, calcium polycarbophil
- Surfactant/osmotic: *docusate, polyethylene glycol (PEG), lactulose
Laxatives: Onset of action of 6-8h
which laxatives & stool characteristics
Soft or semifluid stool
*Stimulants (irritants): *bisacodyl (PO), Senna (PO)
Laxatives: Onset of action of 1-3h
which laxatives & stool characteristics
watery evacuation
- Osmotic (high dose)*: sodium phosphate, magnesium sulfate, milk of magnesia, magnesium citrate
- Stimulants: *bisacodyl suppository
