Pharmacology II Block 2 - Bowel Motility/Constipation
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94 terms
Terms | Definitions |
|---|---|
 How does dopamine produce inhibitory effect in the GI? | suppression of ACh release from myenteric motor neurons |
| Which laxative agent does not significantly decrease small bowel transit time? | Docusate |
| Which agents increase propulsive action, mass actions and stool water? | Magnesium, Anthraquinones and Diphenylmethanes |
| What is the definition of laxation? | evacuation of formed fecal material from the rectum |
| What is the definition of catharsis? | evacuation of unformed watery fecal material from the entire colon |
| What laxative/cathartic agents produce the quickest onset of action? | CEO-TWO suppositories (containing sodium bicarbonate and potassium bitartrate) - onset in 5-30 minutes |
| What is lignin's water solubility and % fermentation? | poor / 0% |
| What is Cellulose's water solubility and % fermentation? | poor / 15% |
| What is Hemicellulose's water solubility and % fermentation? | Good / 56-87% |
| What are Muclages and gums' water solubility and % fermentation? | Good / 85-95% |
| What is Pectins' water solubility and % fermentation? | Good / 90-95% |
| What inputs does the ENS respond to for GI activity? | input from the local environment of the gut as well as the ANS/CNS |
| What are the two aspects of MMC? | migrating myoelectric complex and migrating motor complex |
| How many phases and how long does the MMC cycle last? | four phases over 80-110 minutes |
| Which phase of MMC is the most characteristic? | Phase III - consisting of clusters of rhythmic contractions that occupy short segments of the intestine for a period of 6-10 minutes before proceeding caudally |
| Which phase of MMC is the release of motilin associated with? | Phase II - associated with motility stimulation in the proximal gut |
| What are two key jobs of the MMC? | sweep debris out towards the anus and help limit overgrowth of luminal bacteria |
| How many contractions per minute occur during fed-state? | 12-15 contractions per minute |
| What is peristalsis? | a series of reflex responses to a bolus in the lumen of a given segment of the intestine |
| What does the firing of the ascending excitatory reflex result in and what is its neurotransmitter? | contraction of the circular muscles on the oral side of the bolus / ACh |
| What does the firing of the descending inhibitory reflex result in and what is its neurotransmitter? | relaxation of smooth muscle on the anus side / NO |
| Which mucosal cells are responsible for initiation of peristalsis and what is the neurotransmitter they release? | enterochromaffin cells in the mucosa / serotonin |
| What does control of tension in the GI smooth muscle largely depend on? | Ca concentrations |
| What is the term given to agents who enhance coordinated GI motility and transit of material in the GI tract? | prokinetic agents |
| Why are older cholinomimetic agents and AChE inhibitors not very effective for GI issues? | they enhance contractions in an uncoordinated fashion that doesn't produce propulsive activity |
| What is the role of cholinergic agents? | to increase ACh content and activity on muscarinic/nicotinic receptors |
| What are the two key cholinergic receptors in the GI, and at what ratio do they exist? | M2 and M3 / 4:1 |
| Of the two key cholinergic receptors in the GI, which is the most important in terms of motility? | M3 |
| What is a synthetic choline derivative with broad muscarinic effects? | Bethanechol |
| What is an AChE inhibitor that increases ACh content in the cleft? | Neostigmine |
| What are some effects of increased ACh concentration at muscarinic receptors? | salivation, lacrimation, bronchoconstriction, bradycardia, abdominal cramps, urinary incontinence |
| What are some effects of increased ACh at nicotinic receptors? | depolarizing neuromuscular blockade and muscle paralysis |
| What are some key effects of dopamine inhibition in the GI? | reduction of the LES and intragastric pressures |
| What neurons do dopamine receptor antagonists in the GI hit? | myenteric motor neurons, making them effective prokinetic agents |
| What other role do dopamine receptor antagonists fill besides motility? | relief of N/V by antagonism in the chemoreceptor trigger zone |
| What are two key dopamine receptor antagonists? | Metaclopramide and domperidone |
| What is one of the oldest prokinetic agents which actions on 5-HT4 (agonist) and 5-HT3 (antagonist) receptors, as well as muscarinic and dopamine receptors? | Metaclopramide |
| What effect does metaclopramide have on GI transit? | enhances GI transit, though mostly confined to the upper digestive tract where it increases LES and stimulates antral and small intestinal contractions |
| What is the main therapeutic use of metaclopramide? | Main role is to ameliorate N/V that often accompanies GI dysmotility syndromes |
| What other therapeutic roles does metaclopramide play? | relief of GERD symptoms (but not a healing) and an agent for improving gastric emptying and treating hiccups |
| What dopamine receptor antagonist is predominantly selective for D2 alone and is not available in the US? | Domperidone |
| What role does serotonin play in the GI? | triggers peristaltic reflex by stimulating intrinsic sensory neurons in the myenteric plexus as well as extrinsic vagal and spinal sensory neurons |
| What is a key AE to watch for with SSRIs? | diarrhea (b/c they inhibit reuptake of serotonin, increasing motility) |
| What is the 5-HT1a receptor classification? | inhibitory Gi that increases NO release |
| What is the 5-HT1p receptor classification? | stimulatory Go that causes slow EPSP |
| What is the 5-HT3 receptor classification? | stimulatory ion-channel receptor |
| What is the 5-HT4 receptor classification? | stimulatory Gs that increases ACh release |
| What is a 5-HT4 partial agonist that stimulates motility and Cl secretion leading to increased transit/decreased transit time? | Tegaserod |
| What is the main use of Tegaserod? | only for emergency use for females with constipation-predominant IBS |
| What is an endogenous peptide and a potent contractile agent of the upper GI whose levels fluctuate with MMC? | Motilin |
| What drug mimics the effect of motilin? | erythromycin - induces phase III MMC activity and smooth muscle contractility |
| What is the main role of erythromycin in the GI? | prokinetic agent in patients with diabetic gastroparesis. also used in hospitals preoperative to cleanse out the colon |
| What is the prostanoic acid derivative that activates ClC2 channels? | Lubiprostone |
| What is the role of Lubiprostone? | activates the Cl channel so you get an influx of Cl into the lumen, leading to water flow into the lumen, distension, motility/peristalsis reflex triggering |
| How much of normal stool weight is composed of water? | 70-85% |
| What is the result in the GI if you have too little water in the lumen? | constipation |
| What is the result in the GI if you have too much water in the lumen? | diarrhea |
| What are the three main classifications of laxatives? | luminally active agents, stimulants/irritants and prokinetic agents |
| What are some effects of laxatives? | enhances fluid retention, decreases absorption of fluid and alters motility |
| When you hear bulk-forming laxatives, what should you think of? | Fiber |
| What is fiber? | a food component that resists enzymatic digestion and attracts water |
| What do colonic bacteria do to fiber? | ferment it to make short-chain fatty acids which are nutrients to the bacteria |
| What role can fatty acids play in the GI? | prokinetic effect - inducing peristalsis, increases bacterial mass/stool volume and can also stimulate gas-production |
| What is the general mechanism for the bulk-forming laxatives? | Absorb water --> increase bulk --> stimulate peristalsis |
| What bulk-forming laxative is made from psyllium husk, undergoes significant fermentation, and produces the most gas of the bulk-forming agents? | Metamucil |
| What bulk-forming laxative is a synthetic cellulose that is poorly fermentable? | Citrucel (methylcellulose) |
| What bulk-forming laxative is an acrylic acid resin polymer that is poorly fermentable? | Fibercon (Calcium polycarbophil) |
| What is the main difference between soluble and insoluble fiber? | the former goes through fermentation and causes bloating/flatus / the latter is poorly fermented but better at attracting water |
| What is one main counseling point with taking fiber? | Drink lots of water - otherwise you could end up constipated |
| What agents are known as saline cathartics? | Magnesium citrate, magnesium sulfate, sodium phosphate |
| What is the result of saline laxatives? | very quick acting laxative but with very watery perfuse diarrhea |
| What is the mechanism of action for saline laxatives? | creates an osmotic water retention situation that stimulates peristalsis and can produce inflammatory mediators (not an irritant though) |
| Of Mg and PO4, which requires larger doses and why? | PO4 - they are absorbed to a greater degree so you have to dose more to be therapeutic |
| What classes of patients should avoid the saline laxatives? | renal insufficiency, cardiac disease, electrolyte abnormalities and diuretic therapy |
| What conditions can arise from sodium phosphate treatment for constipation? | hyperphosphatemia, hypernatremia, hypocalcemia, hypokalemia |
| What is a galactose-fructose synthetic disaccharide? | Lactulose |
| What is one indication for the use of lactulose? | hepatic encephalopathy |
| What is the term given to electrolyte solutions used as laxatives? | polyethylene glycol electrolyte solutions (PEG causes the laxative effect) |
| What prevents electrolyte imbalance while taking PEG? | solution is made isotonic with added sodium sulfate, sodium bicarbonate, sodium chloride and potassium chloride |
| What is the MOA of surfactants/stool softeners like docusate? | lowers surface tension of stool, permitting mixing/entry of water and lipids / also stimulates fluid/electrolyte secretion and alters mucosal permeability |
| What is a mixture of aliphatic hydrocarbons that is indigestible with minimal absorption, but penetrates and softens stool up? | mineral oil |
| What is one thing to watch for with long-term use of mineral oil? | malabsorption of the fat-soluble vitamins ADEK |
| What is the MOA of stimulants/irritants? | induces a low-grade inflammation that promotes accumulation of water and electrolytes that eventually stimulates motility |
| What stimulant/irritant can lead to cartharsis and fluid/electrolyte deficits in overdose? | Bisacodyl |
| What stimulant/irritant is converted in the GI to an active form by normal flora of the GI? | Senna |
| what is one adverse effect to watch for with Senna? | melanotic pigmentation of the colon (cathartic colon) |
| Which stimulant/irritant contains two noxious agents (ricin and oil) | Castor Oil |
| How does castor oil work? | lypases hydrolize the triglyceride to yield glycerol and ricinoleic acid (the latter is the active ingredient) |
| What are two examples of opioid receptor antagonists? | Methylnaltrexone and Alvimopan (selective mu-receptor antagonists) |
| Why do the opioid receptor antagonists have no affect on analgesia? | they cannot cross the BBB |
| What specific role is methylnaltrexone used for? | for opioid-induced constipation |
| What role is alvimopan used for? | to shorten duration of post-op ileus |
| What is a major AE of metaclopramide? | EPS (nigrostriatal pathway), particularly after IV administration |
| What is a major AE of erythromycin? | pseudomembranous colitis and induction of resistant strains of bacteria |
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