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Constipation Predispositions

• Movement disorder such as Parkinson’s, (decreased dopamine levels)
• Spinal cord tumor: regulates parasympathetic nervous system
• Diabetes: gastric paresis
• Hypothyroidism: slowed metabolism
• Multiple sclerosis: interruption of nerve impulses leads to a myriad of symptoms including weakness
• Bowel disorders, CV events

 

Offending drugs

• Opioids: constipation is a common side effect.
• Iron: supplement with vitamin C increases absorption.
• Anticholinergics (Antispasmodics, antihistamine, phenothiazine, TCA, incontinence drugs etc.): dry out everything.
• Non-DHP CCBs, clonidine (central alpha-adrenergic agonist): reduced sympathetic effects.
• Bismuth: treats diarrhea and can cause constipation.
• Al containing antacid, excessive Ca can also cause constipation.
• Anti-neoplastic (alkaloids, oxaliplatins, taxane).

 

Laxatives

• For quicker relief chose a rectal product.

Bulk forming: FiberCon, Metamucil, methylcellulose

• Creates gel like matrix in stool, soak up fluids in loose stool, add bulk to hard stool
• 1st line; caution with drugs stick to fiber: digoxin, Li, carbamazepine.

Stool softeners (emollient, lubricant) 

• Docusate (Colace) - Do not use docusate with mineral oil
• mineral oil - take multivitamins at different time

Stimulants: bisacodyl, senna, cascara

• Reduce water and electrolyte absorption by stimulation neurons and irritating the mucosal lining
• Quickest onset.

Osmotic

• Drugs: Mg salts (Milk of Magnesium), Lactulose (Cephulac), polyethylene glycol -PEG (Golytely, Miralax), sorbitol
• MOA: Draw fluid into GI lumen stimulating bowel movements.
• SE: dehydration, do not use in CHF/renal disease (can worsen symptoms such as edema), ↓ Ca and PO
• Lactulose may also be used to treat elevated ammonia or prevent hepatic encephalopathy.
• Mg products: watch out for accumulation in CKD. (worry for any kind of alkali or alkaline metals: Li, Al, etc.)

Opioid blocker: methylnaltreone (Relistor)

• MOA: Blocks opioid receptor in gut.
• SC every other day, reduce dose if CrCl < 30

Lubiprostone (Amitiza)

• MOA: Activates Cl channel in gut, leading to increased fluid and movement in gut
• 24mcg BID WF (8mcg BID for IBS with constipation)
• SE: nausea, Abd pain, distention

Diarrhea

Background

• Most are caused by viruses.
• Coli is the most common bacterial cause. Quinolones are used commonly for bacterial diarrhea. Azithromycin is an alternative. Rifaximin (Xifaxan) is also used for E.Coli (200mg TID x3 ), it is a derivative of rifampin, therefore a strong inducer.
• If infection is parasitical, most likely are caused by Giardia lamblia. Most common treatment is metronidazole 250-500mg QID.
• Medications that can induce diarrhea: Colchicine, metformin, laxatives, antibiotics, antacid containing Mg, misoprostol, quinidine, Li, theophylline, Metoclopramide.
• Toxic megacolon: Usually due to E coli or severe IBS; Caution with Imodium (loperamide) and Lomotil (diphenoxylate/atropine) if GI motility is due to megacolon.

Travelers’ diarrhea (TD)

• Prophylaxis is not recommended, except for those at high risk (immuno-compromised) or critical trip where diarrhea can impact the purpose, then use bismuth subsalicylate (BSS).
• See doctor if high fever or blood in stool.
• Treatment should include fluid and electrolyte, such as Pedialyte, Gatorade.

  

Anti-secretory and antimicrobial

• BSS (Pepto-Bismol): 325mg QID.
• SE: black tongue/stool, salicylate toxicity (may present as tinnitus)
• Caution if on ASA or anticoagulant or renal insufficiency, due to increased bleeding.
• Avoid in children due to risk of Reye's syndrome.

 

Loperamide (Imodium)

• MOA: Acts on intestinal muscle to inhibit peristalsis and slow motility
• 4mg initially, then 2mg after each loose stool, max: 16mg/d.
• Do not self-treat > 2 days, not for children < 2 yo, not in toxic megacolon.

 

Lomotil (diphenoxylate/atropine)

• A combination of a constipating meperidine congener, and atropine (strong anticholinergic property) to discourage abuse.
• SE: sedation, constipation, blurred vision, urinary retention.

 

Sandostatin (octreotide)

• Off label use for diarrhea caused by cancer.

 

Lotronex (alosetron)

• MOA: 5HT3 antagonist for patients who failed Imodium.
• Treatment for diarrhea in IBS.
• Prescriber must enroll PPL (prescribing program for Lotronex), and the Rx must have a PPL sticker.

 

Zelnorm (tegaserod)

• Treatment for constipation in IBS.

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